fed-sx-m2: Step 8b-timer — live retry-loop wiring on send_after

Wires the delivery_worker's retry loop on top of the
erlang:send_after / cancel_timer primitives just landed on
loops/erlang (3709460d, 98b0104c, 779e53b2 — cherry-picked here
since origin/architecture hasn't caught up yet).

Surface:
- new :timers [{Cid, Ref}] state field tracks live timer refs
- handle_call(flush): drain (existing semantics) + arm_retry_timer
  per retried Cid (computes backoff slot from the now-bumped attempt
  count, sets next_retry_at, send_after self-cast). Reply shape
  unchanged.
- handle_info({retry, Cid}, S): redrives that one Cid through
  deliver_one_pure. Success → record_success_pure + clear pending.
  Failure → schedule_retry_for (which bumps attempts, dead-letters on
  slot 6, or arms next slot).
- cancel_timer_for/2 before arming a new timer so stale timers don't
  keep the scheduler's run loop alive after the work is done.
- state_srv/1 + timer_ref_for/2 for test introspection.

5/5 in new delivery_retry_timer.sh; existing delivery_worker.sh
17/17 and delivery_retry.sh 11/11 still green. Conformance gate
771/771 (was 761/761; the +10 is the cherry-picked send_after
suite).

Closes Blockers #3. m2 is now feature-complete.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

hosts/ocaml/bin/run_tests.ml

@@ -67,6 +67,14 @@ let rec deep_equal a b =
   | NativeFn _, NativeFn _ -> a == b
   | _ -> false
 
+(* ====================================================================== *)
+(* Test extensions for the VM extension registry suite (Phase B)           *)
+(* ====================================================================== *)
+
+(* Extend the extensible variant from sx_vm_extension.ml so the test
+   extensions below can carry their own private state. *)
+type Sx_vm_extension.extension_state += TestRegState of int ref
+
 (* ====================================================================== *)
 (* Build evaluator environment with test platform functions                *)
 (* ====================================================================== *)
@@ -1282,7 +1290,827 @@ let run_foundation_tests () =
   let l = { l_params = ["x"]; l_body = Symbol "x"; l_closure = Sx_types.make_env (); l_name = None; l_compiled = None; l_call_count = 0; l_uid = Sx_types.next_lambda_uid () } in
   assert_true "is_lambda" (Bool (Sx_types.is_lambda (Lambda l)));
   ignore (Sx_types.set_lambda_name (Lambda l) "my-fn");
-  assert_eq "lambda name mutated" (String "my-fn") (lambda_name (Lambda l))
+  assert_eq "lambda name mutated" (String "my-fn") (lambda_name (Lambda l));
+
+  Printf.printf "\nSuite: crypto-sha2\n";
+  (* NIST FIPS 180-4 published vectors. *)
+  assert_eq "sha256 empty"
+    (String "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855")
+    (call "crypto-sha256" [String ""]);
+  assert_eq "sha256 abc"
+    (String "ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad")
+    (call "crypto-sha256" [String "abc"]);
+  assert_eq "sha256 896-bit"
+    (String "248d6a61d20638b8e5c026930c3e6039a33ce45964ff2167f6ecedd419db06c1")
+    (call "crypto-sha256"
+       [String "abcdbcdecdefdefgefghfghighijhijkijkljklmklmnlmnomnopnopq"]);
+  assert_eq "sha256 1M 'a'"
+    (String "cdc76e5c9914fb9281a1c7e284d73e67f1809a48a497200e046d39ccc7112cd0")
+    (call "crypto-sha256" [String (String.make 1000000 'a')]);
+  assert_eq "sha512 empty"
+    (String "cf83e1357eefb8bdf1542850d66d8007d620e4050b5715dc83f4a921d36ce9ce47d0d13c5d85f2b0ff8318d2877eec2f63b931bd47417a81a538327af927da3e")
+    (call "crypto-sha512" [String ""]);
+  assert_eq "sha512 abc"
+    (String "ddaf35a193617abacc417349ae20413112e6fa4e89a97ea20a9eeee64b55d39a2192992a274fc1a836ba3c23a3feebbd454d4423643ce80e2a9ac94fa54ca49f")
+    (call "crypto-sha512" [String "abc"]);
+  assert_eq "sha512 896-bit"
+    (String "8e959b75dae313da8cf4f72814fc143f8f7779c6eb9f7fa17299aeadb6889018501d289e4900f7e4331b99dec4b5433ac7d329eeb6dd26545e96e55b874be909")
+    (call "crypto-sha512"
+       [String ("abcdefghbcdefghicdefghijdefghijkefghijklfghijklmghijklmn"
+                ^ "hijklmnoijklmnopjklmnopqklmnopqrlmnopqrsmnopqrstnopqrstu")]);
+
+  Printf.printf "\nSuite: crypto-sha3\n";
+  (* NIST FIPS 202 published vectors. *)
+  assert_eq "sha3-256 empty"
+    (String "a7ffc6f8bf1ed76651c14756a061d662f580ff4de43b49fa82d80a4b80f8434a")
+    (call "crypto-sha3-256" [String ""]);
+  assert_eq "sha3-256 abc"
+    (String "3a985da74fe225b2045c172d6bd390bd855f086e3e9d525b46bfe24511431532")
+    (call "crypto-sha3-256" [String "abc"]);
+  assert_eq "sha3-256 896-bit"
+    (String "41c0dba2a9d6240849100376a8235e2c82e1b9998a999e21db32dd97496d3376")
+    (call "crypto-sha3-256"
+       [String "abcdbcdecdefdefgefghfghighijhijkijkljklmklmnlmnomnopnopq"]);
+  (* 1600-bit message: 0xa3 * 200 — exercises multi-block absorb (>136B). *)
+  assert_eq "sha3-256 1600-bit 0xa3"
+    (String "79f38adec5c20307a98ef76e8324afbfd46cfd81b22e3973c65fa1bd9de31787")
+    (call "crypto-sha3-256" [String (String.make 200 '\xa3')]);
+
+  Printf.printf "\nSuite: dag-cbor\n";
+  let mkdict pairs =
+    let d = Sx_types.make_dict () in
+    List.iter (fun (k, v) -> Hashtbl.replace d k v) pairs;
+    Dict d
+  in
+  let enc v = call "cbor-encode" [v] in
+  (* RFC 8949 Appendix A — minimal-length deterministic encoding. *)
+  assert_eq "cbor 0"        (String "\x00") (enc (Integer 0));
+  assert_eq "cbor 23"       (String "\x17") (enc (Integer 23));
+  assert_eq "cbor 24"       (String "\x18\x18") (enc (Integer 24));
+  assert_eq "cbor 100"      (String "\x18\x64") (enc (Integer 100));
+  assert_eq "cbor 1000"     (String "\x19\x03\xe8") (enc (Integer 1000));
+  assert_eq "cbor 1000000"
+    (String "\x1a\x00\x0f\x42\x40") (enc (Integer 1000000));
+  assert_eq "cbor -1"       (String "\x20") (enc (Integer (-1)));
+  assert_eq "cbor -100"     (String "\x38\x63") (enc (Integer (-100)));
+  assert_eq "cbor -1000"    (String "\x39\x03\xe7") (enc (Integer (-1000)));
+  assert_eq "cbor false"    (String "\xf4") (enc (Bool false));
+  assert_eq "cbor true"     (String "\xf5") (enc (Bool true));
+  assert_eq "cbor null"     (String "\xf6") (enc Nil);
+  assert_eq "cbor \"\""     (String "\x60") (enc (String ""));
+  assert_eq "cbor \"a\""    (String "\x61\x61") (enc (String "a"));
+  assert_eq "cbor \"IETF\"" (String "\x64IETF") (enc (String "IETF"));
+  assert_eq "cbor []"       (String "\x80") (enc (List []));
+  assert_eq "cbor [1,2,3]"
+    (String "\x83\x01\x02\x03")
+    (enc (List [Integer 1; Integer 2; Integer 3]));
+  assert_eq "cbor [1,[2,3],[4,5]]"
+    (String "\x83\x01\x82\x02\x03\x82\x04\x05")
+    (enc (List [Integer 1;
+                List [Integer 2; Integer 3];
+                List [Integer 4; Integer 5]]));
+  assert_eq "cbor {}" (String "\xa0") (enc (mkdict []));
+  assert_eq "cbor {a:1,b:[2,3]}"
+    (String "\xa2\x61\x61\x01\x61\x62\x82\x02\x03")
+    (enc (mkdict ["a", Integer 1; "b", List [Integer 2; Integer 3]]));
+  assert_eq "cbor {a..e:A..E}"
+    (String "\xa5\x61\x61\x61\x41\x61\x62\x61\x42\x61\x63\x61\x43\x61\x64\x61\x44\x61\x65\x61\x45")
+    (enc (mkdict ["a", String "A"; "b", String "B"; "c", String "C";
+                  "d", String "D"; "e", String "E"]));
+  (* Determinism: insertion order + key length must not change bytes.
+     Sort is length-then-bytewise → a, c, bb. *)
+  let d1 = mkdict ["bb", Integer 2; "a", Integer 1; "c", Integer 3] in
+  let d2 = mkdict ["c", Integer 3; "bb", Integer 2; "a", Integer 1] in
+  assert_eq "cbor det order-invariant" (enc d1) (enc d2);
+  assert_eq "cbor det length-then-bytewise"
+    (String "\xa3\x61\x61\x01\x61\x63\x03\x62\x62\x62\x02")
+    (enc d1);
+  (* Round-trip: decode . encode = identity (structural). *)
+  let roundtrip name v =
+    assert_eq ("cbor rt " ^ name) v (call "cbor-decode" [enc v])
+  in
+  roundtrip "int" (Integer 42);
+  roundtrip "neg" (Integer (-99999));
+  roundtrip "str" (String "hello world");
+  roundtrip "bool" (Bool true);
+  roundtrip "nil" Nil;
+  roundtrip "nested"
+    (List [Integer 1; String "x"; List [Bool false; Nil]]);
+  roundtrip "dict"
+    (mkdict ["k", List [Integer 7]; "name", String "z"]);
+
+  Printf.printf "\nSuite: cid\n";
+  let mh_sha256 s = Sx_cid.multihash 0x12 (Sx_cid.unhex (Sx_sha2.sha256_hex s)) in
+  (* Authoritative vectors (independently derived; match well-known
+     IPFS CIDs). raw "abc" and raw "" — codec 0x55. *)
+  assert_eq "cid raw abc"
+    (String "bafkreif2pall7dybz7vecqka3zo24irdwabwdi4wc55jznaq75q7eaavvu")
+    (call "cid-from-bytes" [Integer 0x55; String (mh_sha256 "abc")]);
+  assert_eq "cid raw empty"
+    (String "bafkreihdwdcefgh4dqkjv67uzcmw7ojee6xedzdetojuzjevtenxquvyku")
+    (call "cid-from-bytes" [Integer 0x55; String (mh_sha256 "")]);
+  (* dag-cbor {} — canonical empty-map CID (sha2-256, codec 0x71). *)
+  assert_eq "cid dag-cbor {}"
+    (String "bafyreigbtj4x7ip5legnfznufuopl4sg4knzc2cof6duas4b3q2fy6swua")
+    (call "cid-from-sx" [mkdict []]);
+  (* Determinism: dict key insertion order must not change the CID. *)
+  let cda = call "cid-from-sx" [mkdict ["b", Integer 2; "a", Integer 1]] in
+  let cdb = call "cid-from-sx" [mkdict ["a", Integer 1; "b", Integer 2]] in
+  assert_eq "cid det order-invariant" cda cdb;
+  assert_true "cid multibase 'b' prefix"
+    (Bool (match call "cid-from-sx" [mkdict []] with
+           | String s -> String.length s > 1 && s.[0] = 'b'
+           | _ -> false));
+
+  Printf.printf "\nSuite: ed25519\n";
+  let hx = Sx_ed25519.unhex in
+  let edv pk msg sg = call "ed25519-verify"
+      [String (hx pk); String (hx msg); String (hx sg)] in
+  (* RFC 8032 §7.1 TEST 1-3 (deterministic; re-derived independently). *)
+  assert_eq "ed25519 RFC T1"
+    (Bool true)
+    (edv "d75a980182b10ab7d54bfed3c964073a0ee172f3daa62325af021a68f707511a"
+         ""
+         "e5564300c360ac729086e2cc806e828a84877f1eb8e5d974d873e065224901555fb8821590a33bacc61e39701cf9b46bd25bf5f0595bbe24655141438e7a100b");
+  assert_eq "ed25519 RFC T2"
+    (Bool true)
+    (edv "3d4017c3e843895a92b70aa74d1b7ebc9c982ccf2ec4968cc0cd55f12af4660c"
+         "72"
+         "92a009a9f0d4cab8720e820b5f642540a2b27b5416503f8fb3762223ebdb69da085ac1e43e15996e458f3613d0f11d8c387b2eaeb4302aeeb00d291612bb0c00");
+  assert_eq "ed25519 RFC T3"
+    (Bool true)
+    (edv "fc51cd8e6218a1a38da47ed00230f0580816ed13ba3303ac5deb911548908025"
+         "af82"
+         "6291d657deec24024827e69c3abe01a30ce548a284743a445e3680d7db5ac3ac18ff9b538d16f290ae67f760984dc6594a7c15e9716ed28dc027beceea1ec40a");
+  (* Tampered message -> false. *)
+  assert_eq "ed25519 tampered msg"
+    (Bool false)
+    (edv "fc51cd8e6218a1a38da47ed00230f0580816ed13ba3303ac5deb911548908025"
+         "af83"
+         "6291d657deec24024827e69c3abe01a30ce548a284743a445e3680d7db5ac3ac18ff9b538d16f290ae67f760984dc6594a7c15e9716ed28dc027beceea1ec40a");
+  (* Tampered signature -> false. *)
+  assert_eq "ed25519 tampered sig"
+    (Bool false)
+    (edv "d75a980182b10ab7d54bfed3c964073a0ee172f3daa62325af021a68f707511a"
+         ""
+         "f5564300c360ac729086e2cc806e828a84877f1eb8e5d974d873e065224901555fb8821590a33bacc61e39701cf9b46bd25bf5f0595bbe24655141438e7a100b");
+  (* Total: wrong-length pubkey / sig -> false, no exception. *)
+  assert_eq "ed25519 short pubkey"
+    (Bool false)
+    (call "ed25519-verify" [String "abc"; String ""; String (String.make 64 '\000')]);
+  assert_eq "ed25519 short sig"
+    (Bool false)
+    (call "ed25519-verify"
+       [String (hx "d75a980182b10ab7d54bfed3c964073a0ee172f3daa62325af021a68f707511a");
+        String ""; String "short"]);
+  assert_eq "ed25519 non-string args"
+    (Bool false)
+    (call "ed25519-verify" [Integer 1; Integer 2; Integer 3]);
+
+  Printf.printf "\nSuite: rsa-sha256\n";
+  (* Fixed RSA-2048 vector: one-off python-cryptography keygen +
+     PKCS1v15/SHA-256 sign of "fed-sx phase F rsa test". *)
+  let rhx = Sx_rsa.unhex in
+  let spki = rhx "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" in
+  let rmsg = rhx "6665642d73782070686173652046207273612074657374" in
+  let rsig = rhx "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" in
+  let rsav s m g = call "rsa-sha256-verify" [String s; String m; String g] in
+  assert_eq "rsa valid" (Bool true) (rsav spki rmsg rsig);
+  assert_eq "rsa tampered msg" (Bool false)
+    (rsav spki (rmsg ^ "x") rsig);
+  assert_eq "rsa tampered sig" (Bool false)
+    (rsav spki rmsg
+       (rhx "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"));
+  assert_eq "rsa garbage spki" (Bool false)
+    (rsav "not der" rmsg rsig);
+  assert_eq "rsa non-string args" (Bool false)
+    (call "rsa-sha256-verify" [Integer 1; Integer 2; Integer 3]);
+
+  Printf.printf "\nSuite: file-list-dir\n";
+  let expect_err nm f =
+    (try ignore (f ());
+       incr fail_count; Printf.printf "  FAIL: %s — no error\n" nm
+     with Eval_error _ ->
+       incr pass_count; Printf.printf "  PASS: %s\n" nm
+        | _ ->
+       incr fail_count; Printf.printf "  FAIL: %s — wrong exn\n" nm)
+  in
+  let tmp = Filename.temp_file "fld" "" in
+  Sys.remove tmp; Unix.mkdir tmp 0o755;
+  let touch n = let oc = open_out (Filename.concat tmp n) in close_out oc in
+  touch "b.txt"; touch "a.txt"; touch "c.txt";
+  assert_eq "file-list-dir sorted"
+    (List [String "a.txt"; String "b.txt"; String "c.txt"])
+    (call "file-list-dir" [String tmp]);
+  expect_err "file-list-dir missing"
+    (fun () -> call "file-list-dir" [String (Filename.concat tmp "nope")]);
+  expect_err "file-list-dir not-a-dir"
+    (fun () -> call "file-list-dir" [String (Filename.concat tmp "a.txt")]);
+  expect_err "file-list-dir arity"
+    (fun () -> call "file-list-dir" []);
+  (* best-effort cleanup *)
+  (try List.iter (fun n -> Sys.remove (Filename.concat tmp n))
+         ["a.txt"; "b.txt"; "c.txt"]; Unix.rmdir tmp
+   with _ -> ());
+
+  Printf.printf "\nSuite: vm-extension-dispatch\n";
+  let make_bc op = ({
+    vc_arity = 0; vc_rest_arity = -1; vc_locals = 0;
+    vc_bytecode = [| op |]; vc_constants = [||];
+    vc_bytecode_list = None; vc_constants_list = None;
+  } : Sx_types.vm_code) in
+  let expect_invalid_opcode label op =
+    let globals = Hashtbl.create 1 in
+    try
+      let _ = Sx_vm.execute_module (make_bc op) globals in
+      incr fail_count;
+      Printf.printf "  FAIL: %s — expected Invalid_opcode, got a result\n" label
+    with
+    | Sx_vm.Invalid_opcode n when n = op ->
+      incr pass_count;
+      Printf.printf "  PASS: %s\n" label
+    | exn ->
+      incr fail_count;
+      Printf.printf "  FAIL: %s — unexpected: %s\n" label (Printexc.to_string exn)
+  in
+  expect_invalid_opcode "opcode 200 raises Invalid_opcode 200" 200;
+  expect_invalid_opcode "opcode 224 raises Invalid_opcode 224" 224;
+  expect_invalid_opcode "opcode 247 raises Invalid_opcode 247" 247;
+  (* Opcode 199 sits just below the extension threshold — should fall to the
+     catch-all (Eval_error), proving the threshold is at 200, not 199. *)
+  let globals = Hashtbl.create 1 in
+  (try
+     let _ = Sx_vm.execute_module (make_bc 199) globals in
+     incr fail_count;
+     Printf.printf "  FAIL: opcode 199 — expected Eval_error, got a result\n"
+   with
+   | Sx_vm.Invalid_opcode _ ->
+     incr fail_count;
+     Printf.printf "  FAIL: opcode 199 routed to extension dispatch (threshold wrong)\n"
+   | Sx_types.Eval_error _ ->
+     incr pass_count;
+     Printf.printf "  PASS: opcode 199 stays in core (catch-all)\n"
+   | exn ->
+     incr fail_count;
+     Printf.printf "  FAIL: opcode 199 — unexpected: %s\n" (Printexc.to_string exn));
+
+  Printf.printf "\nSuite: vm-extension-registry\n";
+  (* Sx_vm_extensions self-installs its dispatcher at module init.  Reset
+     the registry so prior loaded extensions don't interfere with this
+     test. *)
+  Sx_vm_extensions._reset_for_tests ();
+  let module TestExt : Sx_vm_extension.EXTENSION = struct
+    let name = "test_reg"
+    let init () = TestRegState (ref 0)
+    let opcodes _st = [
+      (210, "test_reg.OP_PUSH_42", (fun vm _frame ->
+        Sx_vm.push vm (Sx_types.Integer 42)));
+      (211, "test_reg.OP_DOUBLE_TOS", (fun vm _frame ->
+        let v = Sx_vm.pop vm in
+        match v with
+        | Sx_types.Integer n -> Sx_vm.push vm (Sx_types.Integer (n * 2))
+        | _ -> failwith "OP_DOUBLE_TOS: not an integer"));
+    ]
+  end in
+  Sx_vm_extensions.register (module TestExt);
+
+  (match Sx_vm_extensions.id_of_name "test_reg.OP_PUSH_42" with
+   | Some 210 ->
+     incr pass_count;
+     Printf.printf "  PASS: id_of_name resolves opcode\n"
+   | other ->
+     incr fail_count;
+     Printf.printf "  FAIL: id_of_name: got %s\n"
+       (match other with Some n -> string_of_int n | None -> "None"));
+
+  (match Sx_vm_extensions.id_of_name "nonexistent.OP" with
+   | None ->
+     incr pass_count;
+     Printf.printf "  PASS: id_of_name returns None for unknown\n"
+   | Some _ ->
+     incr fail_count;
+     Printf.printf "  FAIL: id_of_name should return None for unknown\n");
+
+  (match Sx_vm_extensions.state_of_extension "test_reg" with
+   | Some (TestRegState _) ->
+     incr pass_count;
+     Printf.printf "  PASS: state_of_extension returns extension state\n"
+   | _ ->
+     incr fail_count;
+     Printf.printf "  FAIL: state_of_extension lookup\n");
+
+  (match Sx_vm_extensions.state_of_extension "nonexistent" with
+   | None ->
+     incr pass_count;
+     Printf.printf "  PASS: state_of_extension None for unknown\n"
+   | Some _ ->
+     incr fail_count;
+     Printf.printf "  FAIL: state_of_extension should be None\n");
+
+  (* End-to-end dispatch through the VM. Bytecode runs OP_PUSH_42 then
+     OP_RETURN (50); execute_module pops the result. *)
+  let make_bc_seq bytes = ({
+    vc_arity = 0; vc_rest_arity = -1; vc_locals = 0;
+    vc_bytecode = bytes; vc_constants = [||];
+    vc_bytecode_list = None; vc_constants_list = None;
+  } : Sx_types.vm_code) in
+  (let globals = Hashtbl.create 1 in
+   try
+     match Sx_vm.execute_module (make_bc_seq [| 210; 50 |]) globals with
+     | Integer 42 ->
+       incr pass_count;
+       Printf.printf "  PASS: dispatch routes opcode 210 -> push 42\n"
+     | other ->
+       incr fail_count;
+       Printf.printf "  FAIL: dispatch opcode 210: got %s\n"
+         (Sx_types.inspect other)
+   with exn ->
+     incr fail_count;
+     Printf.printf "  FAIL: dispatch opcode 210 raised: %s\n"
+       (Printexc.to_string exn));
+
+  (* Compose two extension opcodes: PUSH_42 then DOUBLE_TOS then RETURN.
+     Verifies that successive extension dispatches share VM state. *)
+  (let globals = Hashtbl.create 1 in
+   try
+     match Sx_vm.execute_module (make_bc_seq [| 210; 211; 50 |]) globals with
+     | Integer 84 ->
+       incr pass_count;
+       Printf.printf "  PASS: extension opcodes compose (42 -> 84)\n"
+     | other ->
+       incr fail_count;
+       Printf.printf "  FAIL: composed opcodes: got %s\n"
+         (Sx_types.inspect other)
+   with exn ->
+     incr fail_count;
+     Printf.printf "  FAIL: composed opcodes raised: %s\n"
+       (Printexc.to_string exn));
+
+  (* Duplicate opcode-id detection. *)
+  let module DupExt : Sx_vm_extension.EXTENSION = struct
+    let name = "dup_check"
+    let init () = TestRegState (ref 0)
+    let opcodes _st = [
+      (210, "dup_check.OP_X", (fun _vm _frame -> ()));
+    ]
+  end in
+  (try
+     Sx_vm_extensions.register (module DupExt);
+     incr fail_count;
+     Printf.printf "  FAIL: duplicate opcode id should have raised\n"
+   with Failure _ ->
+     incr pass_count;
+     Printf.printf "  PASS: duplicate opcode id rejected\n");
+
+  (* Out-of-range opcode-id detection. *)
+  let module OutExt : Sx_vm_extension.EXTENSION = struct
+    let name = "out_of_range"
+    let init () = TestRegState (ref 0)
+    let opcodes _st = [
+      (300, "out_of_range.OP_X", (fun _vm _frame -> ()));
+    ]
+  end in
+  (try
+     Sx_vm_extensions.register (module OutExt);
+     incr fail_count;
+     Printf.printf "  FAIL: out-of-range opcode should have raised\n"
+   with Failure _ ->
+     incr pass_count;
+     Printf.printf "  PASS: out-of-range opcode rejected\n");
+
+  (* Duplicate extension-name detection. *)
+  let module SameNameExt : Sx_vm_extension.EXTENSION = struct
+    let name = "test_reg"  (* same as TestExt above *)
+    let init () = TestRegState (ref 0)
+    let opcodes _st = []
+  end in
+  (try
+     Sx_vm_extensions.register (module SameNameExt);
+     incr fail_count;
+     Printf.printf "  FAIL: duplicate extension name should have raised\n"
+   with Failure _ ->
+     incr pass_count;
+     Printf.printf "  PASS: duplicate extension name rejected\n");
+
+  Printf.printf "\nSuite: extension-opcode-id primitive\n";
+  let prim = Hashtbl.find Sx_primitives.primitives "extension-opcode-id" in
+
+  (* Known opcode (registered by TestExt above). *)
+  (match prim [String "test_reg.OP_PUSH_42"] with
+   | Integer 210 ->
+     incr pass_count;
+     Printf.printf "  PASS: primitive returns Integer for registered opcode\n"
+   | other ->
+     incr fail_count;
+     Printf.printf "  FAIL: registered opcode lookup: got %s\n"
+       (Sx_types.inspect other));
+
+  (* Unknown opcode → Nil. *)
+  (match prim [String "nonexistent.OP_X"] with
+   | Nil ->
+     incr pass_count;
+     Printf.printf "  PASS: primitive returns nil for unknown opcode\n"
+   | other ->
+     incr fail_count;
+     Printf.printf "  FAIL: unknown opcode lookup: got %s\n"
+       (Sx_types.inspect other));
+
+  (* Symbol arg also accepted (compilers may pass quoted symbols). *)
+  (match prim [Symbol "test_reg.OP_DOUBLE_TOS"] with
+   | Integer 211 ->
+     incr pass_count;
+     Printf.printf "  PASS: primitive accepts Symbol args\n"
+   | other ->
+     incr fail_count;
+     Printf.printf "  FAIL: symbol arg: got %s\n" (Sx_types.inspect other));
+
+  (* Wrong arity / type raises Eval_error. *)
+  (try
+     let _ = prim [] in
+     incr fail_count;
+     Printf.printf "  FAIL: zero args should have raised\n"
+   with Sx_types.Eval_error _ ->
+     incr pass_count;
+     Printf.printf "  PASS: zero args rejected\n");
+
+  (try
+     let _ = prim [Integer 42] in
+     incr fail_count;
+     Printf.printf "  FAIL: integer arg should have raised\n"
+   with Sx_types.Eval_error _ ->
+     incr pass_count;
+     Printf.printf "  PASS: integer arg rejected\n");
+
+  Printf.printf "\nSuite: extensions/test_ext (canonical extension)\n";
+  (* Phase D: the real test extension lives at lib/extensions/test_ext.ml.
+     Register it on top of the inline test_reg from earlier suites — the
+     two use disjoint opcode IDs (210/211 vs 220/221) so they coexist. *)
+  Test_ext.register ();
+
+  (* Lookup via the public primitive should now find OP_TEST_PUSH_42. *)
+  (match prim [String "test_ext.OP_TEST_PUSH_42"] with
+   | Integer 220 ->
+     incr pass_count;
+     Printf.printf "  PASS: extension-opcode-id finds test_ext.OP_TEST_PUSH_42\n"
+   | other ->
+     incr fail_count;
+     Printf.printf "  FAIL: opcode lookup: got %s\n" (Sx_types.inspect other));
+
+  (* End-to-end: PUSH_42 + DOUBLE_TOS + RETURN. *)
+  (let globals = Hashtbl.create 1 in
+   try
+     match Sx_vm.execute_module (make_bc_seq [| 220; 221; 50 |]) globals with
+     | Integer 84 ->
+       incr pass_count;
+       Printf.printf "  PASS: extensions/test_ext bytecode executes (84)\n"
+     | other ->
+       incr fail_count;
+       Printf.printf "  FAIL: test_ext bytecode result: got %s\n"
+         (Sx_types.inspect other)
+   with exn ->
+     incr fail_count;
+     Printf.printf "  FAIL: test_ext bytecode raised: %s\n"
+       (Printexc.to_string exn));
+
+  (* Disassembly: opcode_name should resolve 220/221 via the registry,
+     not fall back to UNKNOWN_220 / UNKNOWN_221.  disassemble returns a
+     Dict; the instruction list lives at key "bytecode". *)
+  (let code = make_bc_seq [| 220; 221; 50 |] in
+   let dis = Sx_vm.disassemble code in
+   let entries = match dis with
+     | Dict d -> (match Hashtbl.find_opt d "bytecode" with
+                  | Some (List es) -> es
+                  | _ -> [])
+     | _ -> []
+   in
+   let names = List.filter_map (fun entry -> match entry with
+     | Dict d ->
+       (match Hashtbl.find_opt d "opcode" with
+        | Some (String name) -> Some name
+        | _ -> None)
+     | _ -> None) entries
+   in
+   let has name = List.mem name names in
+   if has "test_ext.OP_TEST_PUSH_42" && has "test_ext.OP_TEST_DOUBLE_TOS" then begin
+     incr pass_count;
+     Printf.printf "  PASS: disassemble shows extension opcode names\n"
+   end else begin
+     incr fail_count;
+     Printf.printf "  FAIL: disassemble names: [%s]\n" (String.concat ", " names)
+   end);
+
+  (* Sanity: opcode_name on an unregistered extension opcode still
+     returns UNKNOWN_n.  Pick 230 — out of test_ext's range. *)
+  (match Sx_vm.opcode_name 230 with
+   | "UNKNOWN_230" ->
+     incr pass_count;
+     Printf.printf "  PASS: unregistered ext opcode falls back to UNKNOWN_n\n"
+   | other ->
+     incr fail_count;
+     Printf.printf "  FAIL: opcode_name 230: got %s\n" other);
+
+  (* Per-extension state: invocation_count should reflect the two opcodes
+     that ran in the dispatch test above. *)
+  (match Test_ext.invocation_count () with
+   | Some n when n >= 2 ->
+     incr pass_count;
+     Printf.printf "  PASS: extension state recorded %d invocations\n" n
+   | other ->
+     incr fail_count;
+     Printf.printf "  FAIL: invocation_count: %s\n"
+       (match other with Some n -> string_of_int n | None -> "None"));
+
+  Printf.printf "\nSuite: extensions/erlang_ext (Phase 9h)\n";
+  (* Register the Erlang opcode namespace. Disjoint id range (200-217)
+     from test_ext (220/221) so they coexist. *)
+  Erlang_ext.register ();
+
+  (match prim [String "erlang.OP_PATTERN_TUPLE"] with
+   | Integer 222 ->
+     incr pass_count;
+     Printf.printf "  PASS: extension-opcode-id erlang.OP_PATTERN_TUPLE = 222\n"
+   | other ->
+     incr fail_count;
+     Printf.printf "  FAIL: erlang.OP_PATTERN_TUPLE: got %s\n"
+       (Sx_types.inspect other));
+
+  (match prim [String "erlang.OP_BIF_IS_TUPLE"] with
+   | Integer 239 ->
+     incr pass_count;
+     Printf.printf "  PASS: extension-opcode-id erlang.OP_BIF_IS_TUPLE = 239\n"
+   | other ->
+     incr fail_count;
+     Printf.printf "  FAIL: erlang.OP_BIF_IS_TUPLE: got %s\n"
+       (Sx_types.inspect other));
+
+  (match prim [String "erlang.OP_NONEXISTENT"] with
+   | Nil ->
+     incr pass_count;
+     Printf.printf "  PASS: unknown erlang opcode -> nil\n"
+   | other ->
+     incr fail_count;
+     Printf.printf "  FAIL: unknown erlang opcode: got %s\n"
+       (Sx_types.inspect other));
+
+  (* Phase 10b vertical slice: erlang.OP_BIF_LENGTH (230) is a REAL
+     handler. Build [CONST 0; OP_BIF_LENGTH; RETURN] with an Erlang
+     list [1,2,3] in the constant pool; expect Integer 3. Proves the
+     full path: bytecode -> Sx_vm extension fallthrough -> erlang_ext
+     handler -> correct stack result. *)
+  (let mk_dict kvs =
+     let h = Hashtbl.create 4 in
+     List.iter (fun (k, v) -> Hashtbl.replace h k v) kvs;
+     Sx_types.Dict h in
+   let er_nil = mk_dict [("tag", Sx_types.String "nil")] in
+   let er_cons hd tl =
+     mk_dict [("tag", Sx_types.String "cons");
+              ("head", hd); ("tail", tl)] in
+   let lst = er_cons (Sx_types.Integer 1)
+               (er_cons (Sx_types.Integer 2)
+                  (er_cons (Sx_types.Integer 3) er_nil)) in
+   let code = ({
+     vc_arity = 0; vc_rest_arity = -1; vc_locals = 0;
+     vc_bytecode = [| 1; 0; 0; 230; 50 |];
+     vc_constants = [| lst |];
+     vc_bytecode_list = None; vc_constants_list = None;
+   } : Sx_types.vm_code) in
+   let globals = Hashtbl.create 1 in
+   try
+     match Sx_vm.execute_module code globals with
+     | Integer 3 ->
+       incr pass_count;
+       Printf.printf "  PASS: erlang.OP_BIF_LENGTH [1,2,3] -> 3 (real handler, end-to-end)\n"
+     | other ->
+       incr fail_count;
+       Printf.printf "  FAIL: OP_BIF_LENGTH result: got %s\n"
+         (Sx_types.inspect other)
+   with exn ->
+     incr fail_count;
+     Printf.printf "  FAIL: OP_BIF_LENGTH raised: %s\n"
+       (Printexc.to_string exn));
+
+  (* More real handlers (Phase 10b batch): build a list/tuple constant
+     and exercise HD/TL/TUPLE_SIZE/IS_* end-to-end through the VM. *)
+  (let mk_dict kvs =
+     let h = Hashtbl.create 4 in
+     List.iter (fun (k, v) -> Hashtbl.replace h k v) kvs;
+     Sx_types.Dict h in
+   let er_nil = mk_dict [("tag", Sx_types.String "nil")] in
+   let er_cons hd tl = mk_dict [("tag", Sx_types.String "cons");
+                                ("head", hd); ("tail", tl)] in
+   let er_tuple es = mk_dict [("tag", Sx_types.String "tuple");
+                              ("elements", Sx_types.List es)] in
+   let er_atom nm = mk_dict [("tag", Sx_types.String "atom");
+                             ("name", Sx_types.String nm)] in
+   let lst3 = er_cons (Sx_types.Integer 7)
+                (er_cons (Sx_types.Integer 8)
+                   (er_cons (Sx_types.Integer 9) er_nil)) in
+   let tup3 = er_tuple [Sx_types.Integer 1; Sx_types.Integer 2;
+                        Sx_types.Integer 3] in
+   let run consts bc =
+     let code = ({
+       vc_arity = 0; vc_rest_arity = -1; vc_locals = 0;
+       vc_bytecode = bc; vc_constants = consts;
+       vc_bytecode_list = None; vc_constants_list = None;
+     } : Sx_types.vm_code) in
+     Sx_vm.execute_module code (Hashtbl.create 1) in
+   let nm = function
+     | Sx_types.Dict d ->
+       (match Hashtbl.find_opt d "name" with
+        | Some (Sx_types.String s) -> s | _ -> "?")
+     | _ -> "?" in
+   let check label want got =
+     if got = want then begin
+       incr pass_count;
+       Printf.printf "  PASS: %s\n" label
+     end else begin
+       incr fail_count;
+       Printf.printf "  FAIL: %s: got %s\n" label (Sx_types.inspect got)
+     end in
+   (* HD [7,8,9] -> 7 *)
+   check "OP_BIF_HD [7,8,9] -> 7" (Sx_types.Integer 7)
+     (run [| lst3 |] [| 1;0;0; 231; 50 |]);
+   (* TL [7,8,9] -> [8,9], check its HD = 8 *)
+   check "OP_BIF_TL then HD -> 8" (Sx_types.Integer 8)
+     (run [| lst3 |] [| 1;0;0; 232; 231; 50 |]);
+   (* TUPLE_SIZE {1,2,3} -> 3 *)
+   check "OP_BIF_TUPLE_SIZE {1,2,3} -> 3" (Sx_types.Integer 3)
+     (run [| tup3 |] [| 1;0;0; 234; 50 |]);
+   (* IS_INTEGER 42 -> true ; IS_INTEGER [..] -> false *)
+   (match run [| Sx_types.Integer 42 |] [| 1;0;0; 236; 50 |] with
+    | v when nm v = "true" ->
+      incr pass_count; Printf.printf "  PASS: OP_BIF_IS_INTEGER 42 -> true\n"
+    | v -> incr fail_count;
+      Printf.printf "  FAIL: IS_INTEGER 42: got %s\n" (Sx_types.inspect v));
+   (match run [| lst3 |] [| 1;0;0; 236; 50 |] with
+    | v when nm v = "false" ->
+      incr pass_count; Printf.printf "  PASS: OP_BIF_IS_INTEGER list -> false\n"
+    | v -> incr fail_count;
+      Printf.printf "  FAIL: IS_INTEGER list: got %s\n" (Sx_types.inspect v));
+   (* IS_ATOM atom -> true ; IS_LIST nil -> true ; IS_TUPLE tuple -> true *)
+   (match run [| er_atom "ok" |] [| 1;0;0; 237; 50 |] with
+    | v when nm v = "true" ->
+      incr pass_count; Printf.printf "  PASS: OP_BIF_IS_ATOM ok -> true\n"
+    | v -> incr fail_count;
+      Printf.printf "  FAIL: IS_ATOM: got %s\n" (Sx_types.inspect v));
+   (match run [| er_nil |] [| 1;0;0; 238; 50 |] with
+    | v when nm v = "true" ->
+      incr pass_count; Printf.printf "  PASS: OP_BIF_IS_LIST nil -> true\n"
+    | v -> incr fail_count;
+      Printf.printf "  FAIL: IS_LIST nil: got %s\n" (Sx_types.inspect v));
+   (match run [| tup3 |] [| 1;0;0; 239; 50 |] with
+    | v when nm v = "true" ->
+      incr pass_count; Printf.printf "  PASS: OP_BIF_IS_TUPLE {..} -> true\n"
+    | v -> incr fail_count;
+      Printf.printf "  FAIL: IS_TUPLE: got %s\n" (Sx_types.inspect v));
+   (match run [| tup3 |] [| 1;0;0; 238; 50 |] with
+    | v when nm v = "false" ->
+      incr pass_count; Printf.printf "  PASS: OP_BIF_IS_LIST tuple -> false\n"
+    | v -> incr fail_count;
+      Printf.printf "  FAIL: IS_LIST tuple: got %s\n" (Sx_types.inspect v));
+   (* ELEMENT: element(2, {1,2,3}) -> 2. Calling convention: push
+      Index then Tuple; opcode pops Tuple (TOS) then Index. *)
+   check "OP_BIF_ELEMENT element(2,{1,2,3}) -> 2" (Sx_types.Integer 2)
+     (run [| Sx_types.Integer 2; tup3 |] [| 1;0;0; 1;1;0; 233; 50 |]);
+   check "OP_BIF_ELEMENT element(1,{1,2,3}) -> 1" (Sx_types.Integer 1)
+     (run [| Sx_types.Integer 1; tup3 |] [| 1;0;0; 1;1;0; 233; 50 |]);
+   (* ELEMENT out of range raises *)
+   (let raised =
+      (try ignore (run [| Sx_types.Integer 9; tup3 |]
+                     [| 1;0;0; 1;1;0; 233; 50 |]); false
+       with Sx_types.Eval_error _ -> true) in
+    if raised then begin
+      incr pass_count;
+      Printf.printf "  PASS: OP_BIF_ELEMENT out-of-range raises\n"
+    end else begin
+      incr fail_count;
+      Printf.printf "  FAIL: OP_BIF_ELEMENT out-of-range should raise\n"
+    end);
+   (* LISTS_REVERSE [7,8,9] -> [9,8,7]; verify HD = 9 then HD of TL = 8 *)
+   check "OP_BIF_LISTS_REVERSE then HD -> 9" (Sx_types.Integer 9)
+     (run [| lst3 |] [| 1;0;0; 235; 231; 50 |]);
+   check "OP_BIF_LISTS_REVERSE then TL,HD -> 8" (Sx_types.Integer 8)
+     (run [| lst3 |] [| 1;0;0; 235; 232; 231; 50 |]);
+   (* reverse preserves length *)
+   check "OP_BIF_LISTS_REVERSE then LENGTH -> 3" (Sx_types.Integer 3)
+     (run [| lst3 |] [| 1;0;0; 235; 230; 50 |]));
+
+  (* A still-stubbed opcode (222 = erlang.OP_PATTERN_TUPLE) raises the
+     not-wired Eval_error — confirms the honest-failure path remains
+     for opcodes whose real handlers haven't landed. *)
+  (let globals = Hashtbl.create 1 in
+   try
+     ignore (Sx_vm.execute_module (make_bc_seq [| 222; 50 |]) globals);
+     incr fail_count;
+     Printf.printf "  FAIL: erlang.OP_PATTERN_TUPLE dispatch should have raised\n"
+   with
+   | Sx_types.Eval_error msg
+     when (let needle = "not yet wired" in
+           let nl = String.length needle and ml = String.length msg in
+           let rec scan i =
+             if i + nl > ml then false
+             else if String.sub msg i nl = needle then true
+             else scan (i + 1)
+           in scan 0) ->
+     incr pass_count;
+     Printf.printf "  PASS: erlang opcode dispatch raises not-wired error\n"
+   | exn ->
+     incr fail_count;
+     Printf.printf "  FAIL: unexpected exn: %s\n" (Printexc.to_string exn));
+
+  (match Erlang_ext.dispatch_count () with
+   | Some n when n >= 1 ->
+     incr pass_count;
+     Printf.printf "  PASS: erlang_ext state recorded %d dispatch(es)\n" n
+   | other ->
+     incr fail_count;
+     Printf.printf "  FAIL: dispatch_count: %s\n"
+       (match other with Some n -> string_of_int n | None -> "None"));
+
+  Printf.printf "\nSuite: jit extension-opcode awareness\n";
+  let scan = Sx_vm.bytecode_uses_extension_opcodes in
+  let no_consts = [||] in
+
+  (* Pure core ops: scan reports false. *)
+  (* OP_TRUE OP_RETURN *)
+  if not (scan [| 3; 50 |] no_consts) then begin
+    incr pass_count;
+    Printf.printf "  PASS: pure core bytecode is JIT-eligible\n"
+  end else begin
+    incr fail_count;
+    Printf.printf "  FAIL: pure core bytecode flagged as extension\n"
+  end;
+
+  (* Extension opcode anywhere → true. *)
+  if scan [| 220; 50 |] no_consts then begin
+    incr pass_count;
+    Printf.printf "  PASS: extension opcode detected at head\n"
+  end else begin
+    incr fail_count;
+    Printf.printf "  FAIL: extension opcode at head missed\n"
+  end;
+
+  (* Mixed: core + extension → true. *)
+  if scan [| 3; 220; 50 |] no_consts then begin
+    incr pass_count;
+    Printf.printf "  PASS: extension opcode detected after core ops\n"
+  end else begin
+    incr fail_count;
+    Printf.printf "  FAIL: extension opcode after core ops missed\n"
+  end;
+
+  (* Operand bytes ≥200 must NOT trigger.  CONST u16 with index 220
+     into a synthetic constant pool — the operand is 220 (lo) 0 (hi),
+     not an opcode.  The pool entry at 220 is irrelevant for the scan. *)
+  let big_consts = Array.make 256 Nil in
+  if not (scan [| 1; 220; 0; 50 |] big_consts) then begin
+    incr pass_count;
+    Printf.printf "  PASS: CONST operand ≥200 not a false positive\n"
+  end else begin
+    incr fail_count;
+    Printf.printf "  FAIL: CONST operand ≥200 false-positives as ext op\n"
+  end;
+
+  (* CALL_PRIM has 3 operand bytes (u16 + u8); all ≥200 should not
+     trigger. *)
+  if not (scan [| 52; 220; 200; 200; 50 |] big_consts) then begin
+    incr pass_count;
+    Printf.printf "  PASS: CALL_PRIM operands ≥200 not a false positive\n"
+  end else begin
+    incr fail_count;
+    Printf.printf "  FAIL: CALL_PRIM operands ≥200 false-positive\n"
+  end;
+
+  (* CLOSURE with upvalue descriptors: scan must skip the 2 + 2*n
+     dynamic operand bytes.  Build a synthetic constant pool with a
+     Dict at index 0 declaring upvalue-count 1, descriptors that are
+     ≥200 — the scan should skip them and not trigger.
+
+     Bytecode layout: CLOSURE 0 0  desc_is_local desc_index  RETURN
+                       op    lo hi      210         220       50
+     With upvalue-count = 1, scan must advance past the 2-byte CLOSURE
+     operand AND the 2 descriptor bytes (210, 220), landing on RETURN. *)
+  let cl_consts = Array.make 1 Nil in
+  let dict = Hashtbl.create 1 in
+  Hashtbl.replace dict "upvalue-count" (Integer 1);
+  cl_consts.(0) <- Dict dict;
+  if not (scan [| 51; 0; 0; 210; 220; 50 |] cl_consts) then begin
+    incr pass_count;
+    Printf.printf "  PASS: CLOSURE upvalue descriptors ≥200 skipped\n"
+  end else begin
+    incr fail_count;
+    Printf.printf "  FAIL: CLOSURE upvalue descriptors false-positive\n"
+  end;
+
+  (* Sanity: opcode after CLOSURE+descriptors that IS an extension
+     opcode triggers correctly. *)
+  if scan [| 51; 0; 0; 210; 220; 221; 50 |] cl_consts then begin
+    incr pass_count;
+    Printf.printf "  PASS: extension opcode after CLOSURE detected\n"
+  end else begin
+    incr fail_count;
+    Printf.printf "  FAIL: extension opcode after CLOSURE missed\n"
+  end
 
 
 (* ====================================================================== *)

hosts/ocaml/bin/sx_server.ml

@@ -18,6 +18,20 @@
 
 open Sx_types
 
+(* Force-link Sx_vm_extensions so its module-init runs: installs the
+   extension dispatch fallthrough and registers the `extension-opcode-id`
+   SX primitive. Without a reference here OCaml dead-code-eliminates the
+   module from sx_server.exe (it's only otherwise reached from run_tests),
+   leaving guest-language opcode extensions (Erlang Phase 9, etc.)
+   invisible to the runtime. The applied call is a harmless lookup. *)
+let () = ignore (Sx_vm_extensions.id_of_name "")
+
+(* Register the Erlang opcode extension (Phase 9h) so
+   `extension-opcode-id "erlang.OP_*"` resolves to the host ids the SX
+   stub dispatcher consults. Guarded: a double-register raises Failure,
+   which we swallow so a re-entered server process doesn't die. *)
+let () = try Erlang_ext.register () with Failure _ -> ()
+
 (* ====================================================================== *)
 (* Font measurement via otfm — reads OpenType/TrueType font tables         *)
 (* ====================================================================== *)
@@ -708,6 +722,139 @@ let setup_evaluator_bridge env =
     match args with
     | [e; expr] -> Sx_ref.eval_expr expr e
     | _ -> raise (Eval_error "eval-in-env: (env expr)"));
+
+  (* fed-sx Milestone 1 Step 8 transport. NATIVE ONLY — sockets +
+     threads; deliberately absent from the WASM kernel (registered
+     here in bin/, never in lib/sx_primitives.ml). Minimal HTTP/1.1,
+     Connection: close. handler : req-dict -> resp-dict where
+     req = {:method :path :query :headers :body},
+     resp = {:status :headers :body}. Never returns. *)
+  Sx_primitives.register "http-listen" (fun args ->
+    let strip_cr s =
+      let n = String.length s in
+      if n > 0 && s.[n - 1] = '\r' then String.sub s 0 (n - 1) else s
+    in
+    match args with
+    | [port_v; handler] ->
+      let port = match port_v with
+        | Integer n -> n
+        | Number f -> int_of_float f
+        | _ -> raise (Eval_error "http-listen: (port handler)") in
+      let sock = Unix.socket Unix.PF_INET Unix.SOCK_STREAM 0 in
+      Unix.setsockopt sock Unix.SO_REUSEADDR true;
+      Unix.bind sock
+        (Unix.ADDR_INET (Unix.inet_addr_loopback, port));
+      Unix.listen sock 64;
+      (* SX runtime is shared across threads — serialize handler calls. *)
+      let mtx = Mutex.create () in
+      let reason = function
+        | 200 -> "OK" | 201 -> "Created" | 204 -> "No Content"
+        | 301 -> "Moved Permanently" | 302 -> "Found"
+        | 400 -> "Bad Request" | 401 -> "Unauthorized"
+        | 403 -> "Forbidden" | 404 -> "Not Found"
+        | 405 -> "Method Not Allowed" | 500 -> "Internal Server Error"
+        | _ -> "OK" in
+      let handle fd =
+        (try
+          let ic = Unix.in_channel_of_descr fd in
+          let oc = Unix.out_channel_of_descr fd in
+          let reqline = strip_cr (input_line ic) in
+          (match String.split_on_char ' ' reqline with
+           | meth :: target :: _ ->
+             let path, query =
+               match String.index_opt target '?' with
+               | Some i ->
+                 String.sub target 0 i,
+                 String.sub target (i + 1)
+                   (String.length target - i - 1)
+               | None -> target, "" in
+             let headers = Sx_types.make_dict () in
+             let clen = ref 0 in
+             let rec rdh () =
+               let h = strip_cr (input_line ic) in
+               if h = "" then ()
+               else begin
+                 (match String.index_opt h ':' with
+                  | Some i ->
+                    let name =
+                      String.lowercase_ascii
+                        (String.trim (String.sub h 0 i)) in
+                    let value =
+                      String.trim
+                        (String.sub h (i + 1)
+                           (String.length h - i - 1)) in
+                    Hashtbl.replace headers name (String value);
+                    if name = "content-length" then
+                      (try clen := int_of_string value with _ -> ())
+                  | None -> ());
+                 rdh ()
+               end in
+             rdh ();
+             let body =
+               if !clen > 0 then begin
+                 let b = Bytes.create !clen in
+                 really_input ic b 0 !clen;
+                 Bytes.unsafe_to_string b
+               end else "" in
+             let req = Sx_types.make_dict () in
+             Hashtbl.replace req "method" (String meth);
+             Hashtbl.replace req "path" (String path);
+             Hashtbl.replace req "query" (String query);
+             Hashtbl.replace req "headers" (Dict headers);
+             Hashtbl.replace req "body" (String body);
+             Mutex.lock mtx;
+             let resp =
+               (try Sx_runtime.sx_call handler [Dict req]
+                with e -> Mutex.unlock mtx; raise e) in
+             Mutex.unlock mtx;
+             let getk k = match resp with
+               | Dict h -> Hashtbl.find_opt h k | _ -> None in
+             let status = match getk "status" with
+               | Some (Integer n) -> n
+               | Some (Number f) -> int_of_float f
+               | _ -> 200 in
+             let rbody = match getk "body" with
+               | Some (String s) -> s
+               | Some v -> Sx_types.value_to_string v
+               | None -> "" in
+             let rhdrs = match getk "headers" with
+               | Some (Dict h) ->
+                 Hashtbl.fold (fun k v acc ->
+                   (k, (match v with
+                        | String s -> s
+                        | v -> Sx_types.value_to_string v)) :: acc)
+                   h []
+               | _ -> [] in
+             let buf = Buffer.create 256 in
+             Buffer.add_string buf
+               (Printf.sprintf "HTTP/1.1 %d %s\r\n" status
+                  (reason status));
+             List.iter (fun (k, v) ->
+               Buffer.add_string buf
+                 (Printf.sprintf "%s: %s\r\n" k v)) rhdrs;
+             if not (List.exists
+                       (fun (k, _) ->
+                          String.lowercase_ascii k = "content-type")
+                       rhdrs)
+             then Buffer.add_string buf
+                 "Content-Type: text/plain\r\n";
+             Buffer.add_string buf
+               (Printf.sprintf "Content-Length: %d\r\n"
+                  (String.length rbody));
+             Buffer.add_string buf "Connection: close\r\n\r\n";
+             Buffer.add_string buf rbody;
+             output_string oc (Buffer.contents buf);
+             flush oc
+           | _ -> ())
+         with _ -> ());
+        (try Unix.close fd with _ -> ())
+      in
+      while true do
+        let fd, _ = Unix.accept sock in
+        ignore (Thread.create handle fd)
+      done;
+      Nil
+    | _ -> raise (Eval_error "http-listen: (port handler)"));
   bind "trampoline" (fun args ->
     match args with
     | [v] ->

hosts/ocaml/bin/test_http.sh

@@ -0,0 +1,49 @@
+#!/usr/bin/env bash
+# Phase H test — native-only http-listen primitive.
+# Starts sx_server with a tiny SX echo handler, drives it with curl
+# (GET / POST / 404 / custom header), asserts, then kills it.
+set -u
+cd "$(dirname "$0")/.."
+
+SRV=_build/default/bin/sx_server.exe
+PORT=${HTTP_TEST_PORT:-8911}
+PASS=0
+FAIL=0
+ok()  { echo "  PASS: $1"; PASS=$((PASS+1)); }
+bad() { echo "  FAIL: $1 — $2"; FAIL=$((FAIL+1)); }
+
+if [ ! -x "$SRV" ]; then
+  echo "build sx_server.exe first (dune build bin/sx_server.exe)"; exit 1
+fi
+
+H='(begin (define (h req) (if (= (get req "path") "/echo") {:status 200 :headers {"X-Echo" (get req "method")} :body (str "M=" (get req "method") " P=" (get req "path") " Q=" (get req "query") " B=" (get req "body"))} {:status 404 :body "nope"})) (http-listen '"$PORT"' h))'
+ESC=${H//\"/\\\"}
+
+{ printf '(epoch 1)\n(eval "%s")\n' "$ESC"; sleep 30; } | "$SRV" >/tmp/test_http_srv.out 2>&1 &
+SVPID=$!
+trap 'kill $SVPID 2>/dev/null; wait 2>/dev/null' EXIT
+
+up=0
+for _ in $(seq 1 50); do
+  curl -s -o /dev/null "http://127.0.0.1:$PORT/echo" 2>/dev/null && { up=1; break; }
+  sleep 0.2
+done
+[ "$up" = 1 ] || { echo "  FAIL: server did not start"; cat /tmp/test_http_srv.out; exit 1; }
+
+# GET with query + custom response header.
+g=$(curl -s -i "http://127.0.0.1:$PORT/echo?x=1" | tr -d '\r')
+echo "$g" | grep -q '^HTTP/1.1 200 OK'        && ok "GET status 200"          || bad "GET status" "$g"
+echo "$g" | grep -q '^X-Echo: GET'            && ok "GET custom header"       || bad "GET header" "$g"
+echo "$g" | grep -q '^M=GET P=/echo Q=x=1 B=$' && ok "GET echo body"          || bad "GET body" "$g"
+
+# POST with body.
+p=$(curl -s -X POST --data 'hello' "http://127.0.0.1:$PORT/echo")
+[ "$p" = 'M=POST P=/echo Q= B=hello' ] && ok "POST body echoed" || bad "POST body" "$p"
+
+# 404 path.
+n=$(curl -s -i "http://127.0.0.1:$PORT/missing" | tr -d '\r')
+echo "$n" | grep -q '^HTTP/1.1 404 Not Found' && ok "404 status" || bad "404 status" "$n"
+echo "$n" | grep -q '^nope$'                  && ok "404 body"   || bad "404 body" "$n"
+
+echo "Results: $PASS passed, $FAIL failed"
+[ "$FAIL" = 0 ]

hosts/ocaml/lib/dune

@@ -2,3 +2,7 @@
  (name sx)
  (wrapped false)
  (libraries re re.pcre unix))
+
+; Pull in extension modules from lib/extensions/ (test_ext.ml, etc).
+; See plans/sx-vm-opcode-extension.md.
+(include_subdirs unqualified)

hosts/ocaml/lib/extensions/README.md

@@ -0,0 +1,71 @@
+# SX VM extensions
+
+Each `*.ml` file here is a VM extension — a first-class OCaml module that
+registers specialized bytecode opcodes with `Sx_vm_extensions`. See
+[`plans/sx-vm-opcode-extension.md`](../../../../plans/sx-vm-opcode-extension.md)
+for the design.
+
+## Pattern
+
+```ocaml
+(* lib/extensions/myport.ml *)
+open Sx_types
+
+type Sx_vm_extension.extension_state += MyportState of { ... }
+
+module M : Sx_vm_extension.EXTENSION = struct
+  let name = "myport"
+  let init () = MyportState { ... }
+  let opcodes _st = [
+    (id, "myport.OP_NAME", handler);
+    ...
+  ]
+end
+
+let register () = Sx_vm_extensions.register (module M)
+```
+
+Then call `Myport.register ()` once at startup from any binary that
+should have the extension loaded.
+
+## Opcode-ID allocation
+
+Range 200-247 (per `Sx_vm_extensions.extension_min` /
+`extension_max`).  Conventions:
+
+| Range   | Use                                                                     |
+|---------|-------------------------------------------------------------------------|
+| 200-209 | reserved for `lib/guest/vm/` shared opcodes (chiselled out on 2nd use)  |
+| 210-219 | inline test extensions defined in `bin/run_tests.ml`                    |
+| 220-229 | this directory's `test_ext` (the canonical template)                    |
+| 230-247 | first-come-first-served by language ports (Erlang first)                |
+
+When a port claims a contiguous block, document it in the table above.
+The registry rejects collisions at startup with a loud error — there is
+no silent shadowing.
+
+## Naming
+
+Always prefix opcode names with the extension name plus a dot:
+`myport.OP_<NAME>`.  The prefix is a hard convention so that multiple
+extensions can share the global opcode-name namespace cleanly.
+
+## State
+
+`extension_state` is an extensible variant.  Add your case (e.g.
+`MyportState of { ... }`) at the top of your file, return it from
+`init`, and pattern-match it inside your handlers.  Other extensions
+cannot see your state — the variant case is private to your module.
+
+## Testing
+
+`test_ext.ml` is the canonical worked example.  `bin/run_tests.ml`
+calls `Test_ext.register ()`, then drives bytecode that exercises the
+opcodes end-to-end (push, double, dispatch, disassemble, invocation
+counter).  Mirror this shape when adding a real port's extension.
+
+## Build wiring
+
+`lib/dune` has `(include_subdirs unqualified)`, so any `.ml` you drop
+in here is automatically part of the `sx` library.  Module name follows
+the filename verbatim (`test_ext.ml` → `Test_ext`).

hosts/ocaml/lib/extensions/erlang_ext.ml

@@ -0,0 +1,278 @@
+(** {1 [erlang_ext] — Erlang-on-SX VM opcode extension (Phase 9h)}
+
+    Registers the Erlang opcode namespace in [Sx_vm_extensions] so that
+    [extension-opcode-id "erlang.OP_*"] resolves to a stable id. The SX
+    stub dispatcher in [lib/erlang/vm/dispatcher.sx] consults these ids
+    (Phase 9i) and falls back to its own local ids when the host
+    extension is absent.
+
+    Opcode ids occupy 222-239 in the extension partition (200-247).
+    222+ is chosen to clear the test extensions' reserved ids
+    (test_reg 210/211, test_ext 220/221) so all three coexist in
+    run_tests; production sx_server only registers this one. Names
+    mirror the SX stub dispatcher exactly:
+
+    - 222 erlang.OP_PATTERN_TUPLE      - 231 erlang.OP_BIF_HD
+    - 223 erlang.OP_PATTERN_LIST       - 232 erlang.OP_BIF_TL
+    - 224 erlang.OP_PATTERN_BINARY     - 233 erlang.OP_BIF_ELEMENT
+    - 225 erlang.OP_PERFORM            - 234 erlang.OP_BIF_TUPLE_SIZE
+    - 226 erlang.OP_HANDLE             - 235 erlang.OP_BIF_LISTS_REVERSE
+    - 227 erlang.OP_RECEIVE_SCAN       - 236 erlang.OP_BIF_IS_INTEGER
+    - 228 erlang.OP_SPAWN              - 237 erlang.OP_BIF_IS_ATOM
+    - 229 erlang.OP_SEND               - 238 erlang.OP_BIF_IS_LIST
+    - 230 erlang.OP_BIF_LENGTH         - 239 erlang.OP_BIF_IS_TUPLE
+
+    {2 Handler status}
+
+    The bytecode compiler does not yet emit these opcodes — Erlang
+    programs run through the general CEK path and the working
+    specialization path is the SX stub dispatcher. So every handler
+    here raises a descriptive [Eval_error] rather than silently
+    corrupting the VM stack. This keeps the extension honest: the
+    namespace is registered and disassembles by name, [extension-opcode-id]
+    works, but actually dispatching an opcode (which only happens once a
+    future phase teaches the compiler to emit them) fails loudly with a
+    pointer to the phase that will wire it. Real stack-machine handlers
+    land alongside compiler emission in a later phase. *)
+
+open Sx_types
+
+(** Per-instance state: invocation counter, purely to exercise the
+    [extension_state] machinery (mirrors [test_ext]). *)
+type Sx_vm_extension.extension_state += ErlangExtState of {
+  mutable dispatched : int;
+}
+
+let not_wired name =
+  raise (Eval_error
+    (Printf.sprintf
+       "%s: bytecode emission not yet wired (Phase 9j) — \
+        Erlang runs via CEK; specialization path is the SX stub \
+        dispatcher in lib/erlang/vm/dispatcher.sx"
+       name))
+
+module M : Sx_vm_extension.EXTENSION = struct
+  let name = "erlang"
+  let init () = ErlangExtState { dispatched = 0 }
+
+  let opcodes st =
+    let bump () = match st with
+      | ErlangExtState s -> s.dispatched <- s.dispatched + 1
+      | _ -> ()
+    in
+    let op id nm =
+      (id, nm, (fun (_vm : Sx_vm.vm) (_frame : Sx_vm.frame) ->
+        bump (); not_wired nm))
+    in
+    (* Phase 10b vertical slice: one REAL register-machine handler.
+       erlang.OP_BIF_LENGTH (230) — pops an Erlang list off the VM
+       stack and pushes its length. Proves the full path works:
+       extension-opcode-id -> bytecode -> Sx_vm dispatch fallthrough
+       -> this handler -> correct stack result. The remaining 17
+       opcodes still raise not_wired until their handlers + compiler
+       emission land. Erlang lists are tagged dicts:
+         nil  = {"tag" -> String "nil"}
+         cons = {"tag" -> String "cons"; "head" -> v; "tail" -> v} *)
+    let er_tag d =
+      match Hashtbl.find_opt d "tag" with
+      | Some (String s) -> s | _ -> ""
+    in
+    let op_bif_length =
+      (230, "erlang.OP_BIF_LENGTH",
+       (fun (vm : Sx_vm.vm) (_frame : Sx_vm.frame) ->
+         bump ();
+         let v = Sx_vm.pop vm in
+         let rec walk acc node =
+           match node with
+           | Dict d ->
+             (match er_tag d with
+              | "nil" -> acc
+              | "cons" ->
+                (match Hashtbl.find_opt d "tail" with
+                 | Some t -> walk (acc + 1) t
+                 | None -> raise (Eval_error
+                     "erlang.OP_BIF_LENGTH: cons cell without :tail"))
+              | _ -> raise (Eval_error
+                  "erlang.OP_BIF_LENGTH: not a proper list"))
+           | _ -> raise (Eval_error
+               "erlang.OP_BIF_LENGTH: not a proper list")
+         in
+         Sx_vm.push vm (Integer (walk 0 v))))
+    in
+    (* Phase 10b — simple hot-BIF handlers. Erlang bool is the atom
+       {"tag"->"atom"; "name"->"true"|"false"}; mk_atom builds it. *)
+    let mk_atom nm =
+      let h = Hashtbl.create 2 in
+      Hashtbl.replace h "tag" (String "atom");
+      Hashtbl.replace h "name" (String nm);
+      Dict h
+    in
+    let er_bool b = mk_atom (if b then "true" else "false") in
+    let is_tag v t = match v with
+      | Dict d -> er_tag d = t
+      | _ -> false
+    in
+    let op_bif_hd =
+      (231, "erlang.OP_BIF_HD",
+       (fun (vm : Sx_vm.vm) _f ->
+         bump ();
+         match Sx_vm.pop vm with
+         | Dict d when er_tag d = "cons" ->
+           (match Hashtbl.find_opt d "head" with
+            | Some h -> Sx_vm.push vm h
+            | None -> raise (Eval_error "erlang.OP_BIF_HD: cons without :head"))
+         | _ -> raise (Eval_error "erlang.OP_BIF_HD: not a cons")))
+    in
+    let op_bif_tl =
+      (232, "erlang.OP_BIF_TL",
+       (fun (vm : Sx_vm.vm) _f ->
+         bump ();
+         match Sx_vm.pop vm with
+         | Dict d when er_tag d = "cons" ->
+           (match Hashtbl.find_opt d "tail" with
+            | Some t -> Sx_vm.push vm t
+            | None -> raise (Eval_error "erlang.OP_BIF_TL: cons without :tail"))
+         | _ -> raise (Eval_error "erlang.OP_BIF_TL: not a cons")))
+    in
+    let op_bif_tuple_size =
+      (234, "erlang.OP_BIF_TUPLE_SIZE",
+       (fun (vm : Sx_vm.vm) _f ->
+         bump ();
+         match Sx_vm.pop vm with
+         | Dict d when er_tag d = "tuple" ->
+           let n = match Hashtbl.find_opt d "elements" with
+             | Some (List es) -> List.length es
+             | Some (ListRef r) -> List.length !r
+             | _ -> raise (Eval_error
+                 "erlang.OP_BIF_TUPLE_SIZE: tuple without :elements")
+           in
+           Sx_vm.push vm (Integer n)
+         | _ -> raise (Eval_error "erlang.OP_BIF_TUPLE_SIZE: not a tuple")))
+    in
+    let op_bif_is_integer =
+      (236, "erlang.OP_BIF_IS_INTEGER",
+       (fun (vm : Sx_vm.vm) _f ->
+         bump ();
+         let v = Sx_vm.pop vm in
+         Sx_vm.push vm (er_bool (match v with Integer _ -> true | _ -> false))))
+    in
+    let op_bif_is_atom =
+      (237, "erlang.OP_BIF_IS_ATOM",
+       (fun (vm : Sx_vm.vm) _f ->
+         bump ();
+         let v = Sx_vm.pop vm in
+         Sx_vm.push vm (er_bool (is_tag v "atom"))))
+    in
+    let op_bif_is_list =
+      (238, "erlang.OP_BIF_IS_LIST",
+       (fun (vm : Sx_vm.vm) _f ->
+         bump ();
+         let v = Sx_vm.pop vm in
+         Sx_vm.push vm (er_bool (is_tag v "cons" || is_tag v "nil"))))
+    in
+    let op_bif_is_tuple =
+      (239, "erlang.OP_BIF_IS_TUPLE",
+       (fun (vm : Sx_vm.vm) _f ->
+         bump ();
+         let v = Sx_vm.pop vm in
+         Sx_vm.push vm (er_bool (is_tag v "tuple"))))
+    in
+    (* element/2 and lists:reverse/1 — pure stack transforms (no
+       bytecode operands). Calling convention: args pushed left→right,
+       so element/2 stack is [.. Index Tuple] (Tuple on top). Erlang
+       element/2 is 1-indexed. *)
+    let op_bif_element =
+      (233, "erlang.OP_BIF_ELEMENT",
+       (fun (vm : Sx_vm.vm) _f ->
+         bump ();
+         let tup = Sx_vm.pop vm in
+         let idx = Sx_vm.pop vm in
+         match tup, idx with
+         | Dict d, Integer i when er_tag d = "tuple" ->
+           let es = match Hashtbl.find_opt d "elements" with
+             | Some (List es) -> es
+             | Some (ListRef r) -> !r
+             | _ -> raise (Eval_error
+                 "erlang.OP_BIF_ELEMENT: tuple without :elements")
+           in
+           let n = List.length es in
+           if i < 1 || i > n then
+             raise (Eval_error
+               (Printf.sprintf
+                  "erlang.OP_BIF_ELEMENT: index %d out of range 1..%d" i n))
+           else
+             Sx_vm.push vm (List.nth es (i - 1))
+         | _, Integer _ ->
+           raise (Eval_error "erlang.OP_BIF_ELEMENT: 2nd arg not a tuple")
+         | _ ->
+           raise (Eval_error "erlang.OP_BIF_ELEMENT: 1st arg not an integer")))
+    in
+    let op_bif_lists_reverse =
+      (235, "erlang.OP_BIF_LISTS_REVERSE",
+       (fun (vm : Sx_vm.vm) _f ->
+         bump ();
+         let v = Sx_vm.pop vm in
+         let mk_nil () =
+           let h = Hashtbl.create 1 in
+           Hashtbl.replace h "tag" (String "nil"); Dict h in
+         let mk_cons hd tl =
+           let h = Hashtbl.create 3 in
+           Hashtbl.replace h "tag" (String "cons");
+           Hashtbl.replace h "head" hd;
+           Hashtbl.replace h "tail" tl;
+           Dict h in
+         let rec rev acc node =
+           match node with
+           | Dict d ->
+             (match er_tag d with
+              | "nil" -> acc
+              | "cons" ->
+                let hd = match Hashtbl.find_opt d "head" with
+                  | Some x -> x
+                  | None -> raise (Eval_error
+                      "erlang.OP_BIF_LISTS_REVERSE: cons without :head") in
+                let tl = match Hashtbl.find_opt d "tail" with
+                  | Some x -> x
+                  | None -> raise (Eval_error
+                      "erlang.OP_BIF_LISTS_REVERSE: cons without :tail") in
+                rev (mk_cons hd acc) tl
+              | _ -> raise (Eval_error
+                  "erlang.OP_BIF_LISTS_REVERSE: not a proper list"))
+           | _ -> raise (Eval_error
+               "erlang.OP_BIF_LISTS_REVERSE: not a proper list")
+         in
+         Sx_vm.push vm (rev (mk_nil ()) v)))
+    in
+    [
+      op 222 "erlang.OP_PATTERN_TUPLE";
+      op 223 "erlang.OP_PATTERN_LIST";
+      op 224 "erlang.OP_PATTERN_BINARY";
+      op 225 "erlang.OP_PERFORM";
+      op 226 "erlang.OP_HANDLE";
+      op 227 "erlang.OP_RECEIVE_SCAN";
+      op 228 "erlang.OP_SPAWN";
+      op 229 "erlang.OP_SEND";
+      op_bif_length;
+      op_bif_hd;
+      op_bif_tl;
+      op_bif_element;
+      op_bif_tuple_size;
+      op_bif_lists_reverse;
+      op_bif_is_integer;
+      op_bif_is_atom;
+      op_bif_is_list;
+      op_bif_is_tuple;
+    ]
+end
+
+(** Register [erlang] in [Sx_vm_extensions]. Idempotent only by failing
+    loudly — calling twice raises [Failure]. sx_server calls this once
+    at startup. *)
+let register () = Sx_vm_extensions.register (module M : Sx_vm_extension.EXTENSION)
+
+(** Read the dispatch counter from the live registry state. [None] if
+    [register] hasn't run. *)
+let dispatch_count () =
+  match Sx_vm_extensions.state_of_extension "erlang" with
+  | Some (ErlangExtState s) -> Some s.dispatched
+  | _ -> None

hosts/ocaml/lib/extensions/test_ext.ml

@@ -0,0 +1,67 @@
+(** {1 [test_ext] — canonical example VM extension}
+
+    A minimal extension demonstrating the registration pattern from
+    [plans/sx-vm-opcode-extension.md].  The opcode IDs (220, 221) sit at
+    the top of the extension range, well clear of anything a real
+    language port would claim.
+
+    Two operand-less opcodes:
+
+    - [test_ext.OP_TEST_PUSH_42] (220) — pushes the integer 42.
+    - [test_ext.OP_TEST_DOUBLE_TOS] (221) — pops the integer on TOS,
+      pushes 2× it.
+
+    These are the smallest stack manipulations that prove the extension
+    mechanism wires through end-to-end (registry → dispatch → human-
+    readable disassembly).  Real ports (Erlang Phase 9, future Haskell
+    perf phases) replace this template with their own opcode set.
+
+    Loading: [Test_ext.register ()] adds the extension to
+    [Sx_vm_extensions].  Run-time binaries that want the test opcodes
+    available call this once at startup.  Unit tests in
+    [bin/run_tests.ml] do exactly that. *)
+
+open Sx_types
+
+(** Per-instance state for [test_ext].  Counts how many times the
+    handlers ran — purely so the extension has *some* state, exercising
+    the [extension_state] machinery. *)
+type Sx_vm_extension.extension_state += TestExtState of {
+  mutable invocations : int;
+}
+
+module M : Sx_vm_extension.EXTENSION = struct
+  let name = "test_ext"
+  let init () = TestExtState { invocations = 0 }
+
+  let opcodes st =
+    let bump () = match st with
+      | TestExtState s -> s.invocations <- s.invocations + 1
+      | _ -> ()
+    in
+    [
+      (220, "test_ext.OP_TEST_PUSH_42",
+       (fun vm _frame -> bump (); Sx_vm.push vm (Integer 42)));
+
+      (221, "test_ext.OP_TEST_DOUBLE_TOS",
+       (fun vm _frame ->
+         bump ();
+         let v = Sx_vm.pop vm in
+         match v with
+         | Integer n -> Sx_vm.push vm (Integer (n * 2))
+         | _ -> raise (Eval_error
+             "test_ext.OP_TEST_DOUBLE_TOS: TOS is not an integer")));
+    ]
+end
+
+(** Register [test_ext] in [Sx_vm_extensions].  Idempotent only by
+    failing loudly — calling twice raises [Failure].  Binaries call this
+    once at startup; tests may [_reset_for_tests] then re-register. *)
+let register () = Sx_vm_extensions.register (module M : Sx_vm_extension.EXTENSION)
+
+(** Read the invocation counter from the live registry state.  Returns
+    [None] if [register] hasn't been called yet. *)
+let invocation_count () =
+  match Sx_vm_extensions.state_of_extension "test_ext" with
+  | Some (TestExtState s) -> Some s.invocations
+  | _ -> None

hosts/ocaml/lib/sx_cbor.ml

@@ -0,0 +1,142 @@
+(** dag-cbor encode / decode — pure OCaml, WASM-safe.
+
+    RFC 8949 deterministic subset as constrained by IPLD dag-cbor
+    (RFC 8742): unsigned/negative ints, text strings, arrays, maps
+    with keys sorted by **length-then-bytewise**, bool, null, and
+    tag 42 (CID link, decode-side passthrough). Floats are not
+    supported (no fed-sx shape needs them yet) — encoding a [Number]
+    or decoding a float head raises. Reference: RFC 8949 §3, §4.2. *)
+
+open Sx_types
+
+exception Cbor_error of string
+
+(* ---- Encoder ---- *)
+
+let write_head buf major v =
+  let m = major lsl 5 in
+  if v < 24 then
+    Buffer.add_char buf (Char.chr (m lor v))
+  else if v < 0x100 then begin
+    Buffer.add_char buf (Char.chr (m lor 24));
+    Buffer.add_char buf (Char.chr v)
+  end else if v < 0x10000 then begin
+    Buffer.add_char buf (Char.chr (m lor 25));
+    Buffer.add_char buf (Char.chr ((v lsr 8) land 0xFF));
+    Buffer.add_char buf (Char.chr (v land 0xFF))
+  end else if v < 0x100000000 then begin
+    Buffer.add_char buf (Char.chr (m lor 26));
+    for i = 3 downto 0 do
+      Buffer.add_char buf (Char.chr ((v lsr (8 * i)) land 0xFF))
+    done
+  end else begin
+    Buffer.add_char buf (Char.chr (m lor 27));
+    for i = 7 downto 0 do
+      Buffer.add_char buf (Char.chr ((v lsr (8 * i)) land 0xFF))
+    done
+  end
+
+(* dag-cbor map key order: shorter key first, then bytewise. *)
+let key_order a b =
+  let la = String.length a and lb = String.length b in
+  if la <> lb then compare la lb else compare a b
+
+let rec encode_into buf (v : value) : unit =
+  match v with
+  | Integer n ->
+    if n >= 0 then write_head buf 0 n
+    else write_head buf 1 (-1 - n)
+  | String s ->
+    write_head buf 3 (String.length s);
+    Buffer.add_string buf s
+  | Symbol s | Keyword s ->
+    write_head buf 3 (String.length s);
+    Buffer.add_string buf s
+  | Bool false -> Buffer.add_char buf '\xf4'
+  | Bool true  -> Buffer.add_char buf '\xf5'
+  | Nil        -> Buffer.add_char buf '\xf6'
+  | List items ->
+    write_head buf 4 (List.length items);
+    List.iter (encode_into buf) items
+  | Dict d ->
+    let keys = Hashtbl.fold (fun k _ acc -> k :: acc) d [] in
+    let keys = List.sort_uniq key_order keys in
+    write_head buf 5 (List.length keys);
+    List.iter (fun k ->
+      write_head buf 3 (String.length k);
+      Buffer.add_string buf k;
+      encode_into buf (Hashtbl.find d k)) keys
+  | Number _ ->
+    raise (Cbor_error "cbor-encode: floats unsupported (dag-cbor subset)")
+  | _ ->
+    raise (Cbor_error
+             ("cbor-encode: unencodable value " ^ type_of v))
+
+let encode (v : value) : string =
+  let buf = Buffer.create 64 in
+  encode_into buf v;
+  Buffer.contents buf
+
+(* ---- Decoder ---- *)
+
+let decode (s : string) : value =
+  let pos = ref 0 in
+  let len = String.length s in
+  let byte () =
+    if !pos >= len then raise (Cbor_error "cbor-decode: truncated");
+    let c = Char.code s.[!pos] in incr pos; c
+  in
+  let read_uint ai =
+    if ai < 24 then ai
+    else if ai = 24 then byte ()
+    else if ai = 25 then let a = byte () in let b = byte () in (a lsl 8) lor b
+    else if ai = 26 then begin
+      let v = ref 0 in
+      for _ = 0 to 3 do v := (!v lsl 8) lor byte () done; !v
+    end else if ai = 27 then begin
+      let v = ref 0 in
+      for _ = 0 to 7 do v := (!v lsl 8) lor byte () done; !v
+    end else raise (Cbor_error "cbor-decode: bad additional info")
+  in
+  let read_bytes n =
+    if !pos + n > len then raise (Cbor_error "cbor-decode: truncated");
+    let r = String.sub s !pos n in pos := !pos + n; r
+  in
+  let rec item () =
+    let b = byte () in
+    let major = b lsr 5 and ai = b land 0x1f in
+    match major with
+    | 0 -> Integer (read_uint ai)
+    | 1 -> Integer (-1 - read_uint ai)
+    | 2 -> String (read_bytes (read_uint ai))
+    | 3 -> String (read_bytes (read_uint ai))
+    | 4 ->
+      let n = read_uint ai in
+      List (List.init n (fun _ -> item ()))
+    | 5 ->
+      let n = read_uint ai in
+      let d = make_dict () in
+      for _ = 1 to n do
+        let k = match item () with
+          | String k -> k
+          | _ -> raise (Cbor_error "cbor-decode: non-string map key")
+        in
+        Hashtbl.replace d k (item ())
+      done;
+      Dict d
+    | 6 ->
+      (* Tag: tag-42 CID link → pass the inner item through. *)
+      ignore (read_uint ai); item ()
+    | 7 ->
+      (match ai with
+       | 20 -> Bool false
+       | 21 -> Bool true
+       | 22 -> Nil
+       | 23 -> Nil
+       | _ ->
+         raise (Cbor_error
+                  "cbor-decode: floats/simple unsupported (dag-cbor subset)"))
+    | _ -> raise (Cbor_error "cbor-decode: bad major type")
+  in
+  let v = item () in
+  v

hosts/ocaml/lib/sx_cid.ml

@@ -0,0 +1,66 @@
+(** CIDv1 computation — pure OCaml, WASM-safe.
+
+    Multihash + CIDv1 + multibase base32-lower (RFC 4648, no pad,
+    multibase prefix 'b'). Codecs: dag-cbor 0x71, raw 0x55. Hash
+    codes: sha2-256 0x12, sha3-256 0x16. Reference: the multiformats
+    specs (unsigned-varint, multihash, cid, multibase). No deps. *)
+
+open Sx_types
+
+(* Unsigned LEB128 (multiformats unsigned-varint). *)
+let varint (n : int) : string =
+  let buf = Buffer.create 4 in
+  let n = ref n in
+  let cont = ref true in
+  while !cont do
+    let b = !n land 0x7f in
+    n := !n lsr 7;
+    if !n = 0 then (Buffer.add_char buf (Char.chr b); cont := false)
+    else Buffer.add_char buf (Char.chr (b lor 0x80))
+  done;
+  Buffer.contents buf
+
+(* RFC 4648 base32 lowercase, no padding. *)
+let b32_alpha = "abcdefghijklmnopqrstuvwxyz234567"
+
+let base32_lower (s : string) : string =
+  let buf = Buffer.create ((String.length s * 8 + 4) / 5) in
+  let acc = ref 0 and bits = ref 0 in
+  String.iter (fun c ->
+    acc := (!acc lsl 8) lor (Char.code c);
+    bits := !bits + 8;
+    while !bits >= 5 do
+      bits := !bits - 5;
+      Buffer.add_char buf b32_alpha.[(!acc lsr !bits) land 0x1f]
+    done) s;
+  if !bits > 0 then
+    Buffer.add_char buf b32_alpha.[(!acc lsl (5 - !bits)) land 0x1f];
+  Buffer.contents buf
+
+(* "abef" -> the 2 raw bytes. *)
+let unhex (h : string) : string =
+  let n = String.length h / 2 in
+  let b = Bytes.create n in
+  for i = 0 to n - 1 do
+    Bytes.set b i
+      (Char.chr (int_of_string ("0x" ^ String.sub h (2 * i) 2)))
+  done;
+  Bytes.unsafe_to_string b
+
+(* multihash = varint(code) || varint(len) || digest *)
+let multihash (code : int) (digest : string) : string =
+  varint code ^ varint (String.length digest) ^ digest
+
+(* CIDv1 = 0x01 || varint(codec) || multihash ; multibase 'b' base32. *)
+let cidv1 (codec : int) (mh : string) : string =
+  "b" ^ base32_lower ("\x01" ^ varint codec ^ mh)
+
+let codec_dag_cbor = 0x71
+let mh_sha2_256 = 0x12
+
+(* Canonicalize an SX value: dag-cbor encode -> sha2-256 ->
+   multihash -> CIDv1 (dag-cbor codec). *)
+let cid_from_sx (v : value) : string =
+  let cbor = Sx_cbor.encode v in
+  let digest = unhex (Sx_sha2.sha256_hex cbor) in
+  cidv1 codec_dag_cbor (multihash mh_sha2_256 digest)

hosts/ocaml/lib/sx_ed25519.ml

@@ -0,0 +1,289 @@
+(** Ed25519 signature verification — pure OCaml, WASM-safe.
+
+    RFC 8032 §5.1.7 cofactorless verify over edwards25519. Includes a
+    minimal arbitrary-precision unsigned bignum (no Zarith / no deps)
+    and twisted-Edwards extended-coordinate point arithmetic. Verify
+    is total: malformed inputs return [false], never raise. SHA-512
+    is reused from {!Sx_sha2}. Reference: RFC 8032, RFC 7748. *)
+
+(* ---- Minimal bignum: int array, little-endian, base 2^26. ---- *)
+
+let bits = 26
+let base = 1 lsl bits
+let mask = base - 1
+
+type bn = int array  (* normalized: no high zero limbs, length >= 1 *)
+
+let norm (a : bn) : bn =
+  let n = ref (Array.length a) in
+  while !n > 1 && a.(!n - 1) = 0 do decr n done;
+  if !n = Array.length a then a else Array.sub a 0 !n
+
+let bzero : bn = [| 0 |]
+let of_int n : bn =
+  if n = 0 then bzero
+  else begin
+    let r = ref [] and n = ref n in
+    while !n > 0 do r := (!n land mask) :: !r; n := !n lsr bits done;
+    norm (Array.of_list (List.rev !r))
+  end
+
+let is_zero (a : bn) = Array.length a = 1 && a.(0) = 0
+
+let cmp (a : bn) (b : bn) : int =
+  let a = norm a and b = norm b in
+  let la = Array.length a and lb = Array.length b in
+  if la <> lb then compare la lb
+  else begin
+    let r = ref 0 and i = ref (la - 1) in
+    while !r = 0 && !i >= 0 do
+      if a.(!i) <> b.(!i) then r := compare a.(!i) b.(!i);
+      decr i
+    done; !r
+  end
+
+let add (a : bn) (b : bn) : bn =
+  let la = Array.length a and lb = Array.length b in
+  let n = (max la lb) + 1 in
+  let r = Array.make n 0 in
+  let carry = ref 0 in
+  for i = 0 to n - 1 do
+    let s = !carry
+            + (if i < la then a.(i) else 0)
+            + (if i < lb then b.(i) else 0) in
+    r.(i) <- s land mask; carry := s lsr bits
+  done;
+  norm r
+
+(* a - b, requires a >= b *)
+let sub (a : bn) (b : bn) : bn =
+  let la = Array.length a and lb = Array.length b in
+  let r = Array.make la 0 in
+  let borrow = ref 0 in
+  for i = 0 to la - 1 do
+    let s = a.(i) - !borrow - (if i < lb then b.(i) else 0) in
+    if s < 0 then (r.(i) <- s + base; borrow := 1)
+    else (r.(i) <- s; borrow := 0)
+  done;
+  norm r
+
+let mul (a : bn) (b : bn) : bn =
+  let la = Array.length a and lb = Array.length b in
+  let r = Array.make (la + lb) 0 in
+  for i = 0 to la - 1 do
+    let carry = ref 0 in
+    for j = 0 to lb - 1 do
+      let s = r.(i + j) + a.(i) * b.(j) + !carry in
+      r.(i + j) <- s land mask; carry := s lsr bits
+    done;
+    r.(i + lb) <- r.(i + lb) + !carry
+  done;
+  norm r
+
+let numbits (a : bn) : int =
+  let a = norm a in
+  let hi = Array.length a - 1 in
+  if hi = 0 && a.(0) = 0 then 0
+  else begin
+    let b = ref 0 and v = ref a.(hi) in
+    while !v > 0 do incr b; v := !v lsr 1 done;
+    hi * bits + !b
+  end
+
+let bit (a : bn) (i : int) : int =
+  let limb = i / bits and off = i mod bits in
+  if limb >= Array.length a then 0 else (a.(limb) lsr off) land 1
+
+(* r = a mod m  (m > 0), binary long division. *)
+let bn_mod (a : bn) (m : bn) : bn =
+  if cmp a m < 0 then norm a
+  else begin
+    let r = ref bzero in
+    for i = numbits a - 1 downto 0 do
+      (* r = r*2 + bit *)
+      r := add !r !r;
+      if bit a i = 1 then r := add !r [| 1 |];
+      if cmp !r m >= 0 then r := sub !r m
+    done;
+    !r
+  end
+
+let div_small (a : bn) (d : int) : bn =
+  let la = Array.length a in
+  let q = Array.make la 0 in
+  let rem = ref 0 in
+  for i = la - 1 downto 0 do
+    let cur = (!rem lsl bits) lor a.(i) in
+    q.(i) <- cur / d; rem := cur mod d
+  done;
+  norm q
+
+let powmod (b0 : bn) (e : bn) (m : bn) : bn =
+  let result = ref [| 1 |] and b = ref (bn_mod b0 m) in
+  let nb = numbits e in
+  for i = 0 to nb - 1 do
+    if bit e i = 1 then result := bn_mod (mul !result !b) m;
+    b := bn_mod (mul !b !b) m
+  done;
+  !result
+
+let of_bytes_le (s : string) : bn =
+  let acc = ref bzero in
+  for i = String.length s - 1 downto 0 do
+    acc := add (mul !acc (of_int 256)) (of_int (Char.code s.[i]))
+  done;
+  !acc
+
+let to_bytes_le (a : bn) (n : int) : string =
+  let b = Bytes.make n '\000' in
+  let cur = ref (norm a) in
+  for i = 0 to n - 1 do
+    let q = div_small !cur 256 in
+    let r =
+      let qm = mul q (of_int 256) in
+      let d = sub !cur qm in
+      if is_zero d then 0 else d.(0)
+    in
+    Bytes.set b i (Char.chr r);
+    cur := q
+  done;
+  Bytes.unsafe_to_string b
+
+(* ---- Field GF(p), p = 2^255 - 19 ---- *)
+
+let p =
+  let twop255 = Array.make 11 0 in   (* 11*26 = 286 > 255 *)
+  let limb = 255 / bits and off = 255 mod bits in
+  twop255.(limb) <- 1 lsl off;
+  sub (norm twop255) (of_int 19)
+
+let fmod a = bn_mod a p
+let fadd a b = fmod (add a b)
+let fsub a b = fmod (add a (sub p (fmod b)))
+let fmul a b = fmod (mul a b)
+let fpow a e = powmod a e p
+let finv a = fpow a (sub p (of_int 2))   (* Fermat: a^(p-2) *)
+
+(* group order L = 2^252 + 27742317777372353535851937790883648493 *)
+let ell =
+  of_bytes_le
+    "\xed\xd3\xf5\x5c\x1a\x63\x12\x58\xd6\x9c\xf7\xa2\xde\xf9\xde\x14\
+     \x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x10"
+
+(* d = -121665 / 121666 mod p *)
+let dconst =
+  let inv666 = finv (of_int 121666) in
+  fmod (mul (fsub (of_int 0) (of_int 121665)) inv666)
+
+(* sqrt(-1) = 2^((p-1)/4) mod p *)
+let sqrtm1 = fpow (of_int 2) (div_small (sub p (of_int 1)) 4)
+
+(* ---- edwards25519 points in extended coords (X,Y,Z,T) ---- *)
+
+type pt = { x : bn; y : bn; z : bn; t : bn }
+
+let identity = { x = bzero; y = of_int 1; z = of_int 1; t = bzero }
+
+(* add-2008-hwcd-3, complete for a = -1 on ed25519 *)
+let padd (p1 : pt) (p2 : pt) : pt =
+  let a = fmul (fsub p1.y p1.x) (fsub p2.y p2.x) in
+  let b = fmul (fadd p1.y p1.x) (fadd p2.y p2.x) in
+  let c = fmul (fmul p1.t (fmul (of_int 2) dconst)) p2.t in
+  let dd = fmul (fmul p1.z (of_int 2)) p2.z in
+  let e = fsub b a in
+  let f = fsub dd c in
+  let g = fadd dd c in
+  let h = fadd b a in
+  { x = fmul e f; y = fmul g h; t = fmul e h; z = fmul f g }
+
+let scalar_mul (n : bn) (q : pt) : pt =
+  let r = ref identity in
+  for i = numbits n - 1 downto 0 do
+    r := padd !r !r;
+    if bit n i = 1 then r := padd !r q
+  done;
+  !r
+
+let pnegate (q : pt) : pt =
+  { q with x = fsub (of_int 0) q.x; t = fsub (of_int 0) q.t }
+
+(* Decompress a 32-byte little-endian point encoding. *)
+let decompress (s : string) : pt option =
+  if String.length s <> 32 then None
+  else begin
+    let sign = (Char.code s.[31] lsr 7) land 1 in
+    let s' = Bytes.of_string s in
+    Bytes.set s' 31 (Char.chr (Char.code s.[31] land 0x7f));
+    let y = of_bytes_le (Bytes.unsafe_to_string s') in
+    if cmp y p >= 0 then None
+    else begin
+      let y2 = fmul y y in
+      let u = fsub y2 (of_int 1) in
+      let v = fadd (fmul dconst y2) (of_int 1) in
+      (* x = u v^3 (u v^7)^((p-5)/8) *)
+      let v3 = fmul (fmul v v) v in
+      let v7 = fmul (fmul v3 v3) v in
+      let exp = div_small (sub p (of_int 5)) 8 in
+      let x0 = fmul (fmul u v3) (fpow (fmul u v7) exp) in
+      let vx2 = fmul v (fmul x0 x0) in
+      let x =
+        if cmp vx2 u = 0 then Some x0
+        else if cmp vx2 (fsub (of_int 0) u) = 0 then Some (fmul x0 sqrtm1)
+        else None
+      in
+      match x with
+      | None -> None
+      | Some x ->
+        if is_zero x && sign = 1 then None
+        else begin
+          let x = if (bit x 0) <> sign then fsub (of_int 0) x else x in
+          Some { x; y; z = of_int 1; t = fmul x y }
+        end
+    end
+  end
+
+(* Encode a point to 32-byte little-endian (y with x-parity bit). *)
+let encode (q : pt) : string =
+  let zi = finv q.z in
+  let x = fmul q.x zi and y = fmul q.y zi in
+  let b = Bytes.of_string (to_bytes_le y 32) in
+  let last = Char.code (Bytes.get b 31) lor ((bit x 0) lsl 7) in
+  Bytes.set b 31 (Char.chr last);
+  Bytes.unsafe_to_string b
+
+(* base point: y = 4/5 mod p, x even (sign 0). *)
+let base_point =
+  let by = fmul (of_int 4) (finv (of_int 5)) in
+  match decompress (to_bytes_le by 32) with
+  | Some pt -> pt
+  | None -> failwith "ed25519: base point decompress failed"
+
+let unhex (h : string) : string =
+  let n = String.length h / 2 in
+  let b = Bytes.create n in
+  for i = 0 to n - 1 do
+    Bytes.set b i
+      (Char.chr (int_of_string ("0x" ^ String.sub h (2 * i) 2)))
+  done;
+  Bytes.unsafe_to_string b
+
+let sha512_bytes s = unhex (Sx_sha2.sha512_hex s)
+
+(* RFC 8032 §5.1.7 cofactorless: encode([S]B - [k]A) == R. *)
+let verify ~pubkey ~msg ~sig_ : bool =
+  if String.length pubkey <> 32 || String.length sig_ <> 64 then false
+  else
+    let rb = String.sub sig_ 0 32 in
+    let sb = String.sub sig_ 32 32 in
+    let s = of_bytes_le sb in
+    if cmp s ell >= 0 then false
+    else
+      match decompress pubkey with
+      | None -> false
+      | Some a ->
+        let h = sha512_bytes (rb ^ pubkey ^ msg) in
+        let k = bn_mod (of_bytes_le h) ell in
+        let sb_pt = scalar_mul s base_point in
+        let ka = scalar_mul k a in
+        let chk = padd sb_pt (pnegate ka) in
+        (try encode chk = rb with _ -> false)

hosts/ocaml/lib/sx_primitives.ml

@@ -3237,6 +3237,21 @@ let () =
       with Sys_error msg -> raise (Eval_error ("file-read: " ^ msg)))
     | _ -> raise (Eval_error "file-read: (path)"));
 
+  (* fed-sx Step 3 segment replay. Sorted names, no "."/".." ;
+     errors prefixed like file-read (msg carries enoent/enotdir). *)
+  register "file-list-dir" (fun args ->
+    match args with
+    | [String path] ->
+      (try
+        let names = Sys.readdir path in
+        let names =
+          Array.to_list names
+          |> List.filter (fun n -> n <> "." && n <> "..") in
+        let names = List.sort compare names in
+        List (List.map (fun n -> String n) names)
+      with Sys_error msg -> raise (Eval_error ("file-list-dir: " ^ msg)))
+    | _ -> raise (Eval_error "file-list-dir: (path)"));
+
   register "file-write" (fun args ->
     match args with
     | [String path; String content] ->
@@ -4158,4 +4173,61 @@ let () =
     Sx_types.jit_skipped_count := 0;
     Sx_types.jit_threshold_skipped_count := 0;
     Sx_types.jit_evicted_count := 0;
-    Nil)
+    Nil);
+
+  (* fed-sx host primitives — pure-OCaml crypto (WASM-safe). *)
+  register "crypto-sha256" (fun args ->
+    match args with
+    | [String s] -> String (Sx_sha2.sha256_hex s)
+    | _ -> raise (Eval_error "crypto-sha256: (bytes)"));
+
+  register "crypto-sha512" (fun args ->
+    match args with
+    | [String s] -> String (Sx_sha2.sha512_hex s)
+    | _ -> raise (Eval_error "crypto-sha512: (bytes)"));
+
+  register "crypto-sha3-256" (fun args ->
+    match args with
+    | [String s] -> String (Sx_sha3.sha3_256_hex s)
+    | _ -> raise (Eval_error "crypto-sha3-256: (bytes)"));
+
+  register "cbor-encode" (fun args ->
+    match args with
+    | [v] ->
+      (try String (Sx_cbor.encode v)
+       with Sx_cbor.Cbor_error m -> raise (Eval_error m))
+    | _ -> raise (Eval_error "cbor-encode: (value)"));
+
+  register "cbor-decode" (fun args ->
+    match args with
+    | [String s] ->
+      (try Sx_cbor.decode s
+       with Sx_cbor.Cbor_error m -> raise (Eval_error m))
+    | _ -> raise (Eval_error "cbor-decode: (bytes)"));
+
+  register "cid-from-bytes" (fun args ->
+    match args with
+    | [Integer codec; String mh] ->
+      String (Sx_cid.cidv1 codec mh)
+    | _ -> raise (Eval_error "cid-from-bytes: (codec multihash-bytes)"));
+
+  register "cid-from-sx" (fun args ->
+    match args with
+    | [v] ->
+      (try String (Sx_cid.cid_from_sx v)
+       with Sx_cbor.Cbor_error m -> raise (Eval_error m))
+    | _ -> raise (Eval_error "cid-from-sx: (value)"));
+
+  (* Verify is total: any malformed input -> false, never raises. *)
+  register "ed25519-verify" (fun args ->
+    match args with
+    | [String pk; String msg; String sg] ->
+      Bool (try Sx_ed25519.verify ~pubkey:pk ~msg ~sig_:sg
+            with _ -> false)
+    | _ -> Bool false);
+
+  register "rsa-sha256-verify" (fun args ->
+    match args with
+    | [String spki; String msg; String sg] ->
+      Bool (try Sx_rsa.verify ~spki ~msg ~sig_:sg with _ -> false)
+    | _ -> Bool false)

hosts/ocaml/lib/sx_rsa.ml

@@ -0,0 +1,220 @@
+(** RSASSA-PKCS1-v1_5 verification with SHA-256 — pure OCaml,
+    WASM-safe. Self-contained minimal bignum (modexp only), a tiny
+    DER reader for SubjectPublicKeyInfo, and the fixed SHA-256
+    DigestInfo prefix. Verify only on public data — constant time
+    not required. Reference: RFC 8017 §8.2.2, §9.2. No deps. *)
+
+(* ---- Minimal unsigned bignum: int array, little-endian, base 2^26 ---- *)
+
+let bits = 26
+let base = 1 lsl bits
+let mask = base - 1
+
+type bn = int array
+
+let norm a =
+  let n = ref (Array.length a) in
+  while !n > 1 && a.(!n - 1) = 0 do decr n done;
+  if !n = Array.length a then a else Array.sub a 0 !n
+
+let bzero : bn = [| 0 |]
+let is_zero a = Array.length a = 1 && a.(0) = 0
+
+let cmp a b =
+  let a = norm a and b = norm b in
+  let la = Array.length a and lb = Array.length b in
+  if la <> lb then compare la lb
+  else begin
+    let r = ref 0 and i = ref (la - 1) in
+    while !r = 0 && !i >= 0 do
+      if a.(!i) <> b.(!i) then r := compare a.(!i) b.(!i);
+      decr i
+    done; !r
+  end
+
+let add a b =
+  let la = Array.length a and lb = Array.length b in
+  let n = (max la lb) + 1 in
+  let r = Array.make n 0 and carry = ref 0 in
+  for i = 0 to n - 1 do
+    let s = !carry + (if i < la then a.(i) else 0)
+            + (if i < lb then b.(i) else 0) in
+    r.(i) <- s land mask; carry := s lsr bits
+  done;
+  norm r
+
+let sub a b =                       (* requires a >= b *)
+  let la = Array.length a and lb = Array.length b in
+  let r = Array.make la 0 and borrow = ref 0 in
+  for i = 0 to la - 1 do
+    let s = a.(i) - !borrow - (if i < lb then b.(i) else 0) in
+    if s < 0 then (r.(i) <- s + base; borrow := 1)
+    else (r.(i) <- s; borrow := 0)
+  done;
+  norm r
+
+let mul a b =
+  let la = Array.length a and lb = Array.length b in
+  let r = Array.make (la + lb) 0 in
+  for i = 0 to la - 1 do
+    let carry = ref 0 in
+    for j = 0 to lb - 1 do
+      let s = r.(i + j) + a.(i) * b.(j) + !carry in
+      r.(i + j) <- s land mask; carry := s lsr bits
+    done;
+    r.(i + lb) <- r.(i + lb) + !carry
+  done;
+  norm r
+
+let numbits a =
+  let a = norm a in
+  let hi = Array.length a - 1 in
+  if hi = 0 && a.(0) = 0 then 0
+  else begin
+    let b = ref 0 and v = ref a.(hi) in
+    while !v > 0 do incr b; v := !v lsr 1 done;
+    hi * bits + !b
+  end
+
+let bit a i =
+  let limb = i / bits and off = i mod bits in
+  if limb >= Array.length a then 0 else (a.(limb) lsr off) land 1
+
+let bn_mod a m =                    (* binary long division, m > 0 *)
+  if cmp a m < 0 then norm a
+  else begin
+    let r = ref bzero in
+    for i = numbits a - 1 downto 0 do
+      r := add !r !r;
+      if bit a i = 1 then r := add !r [| 1 |];
+      if cmp !r m >= 0 then r := sub !r m
+    done;
+    !r
+  end
+
+let powmod b0 e m =
+  let result = ref [| 1 |] and b = ref (bn_mod b0 m) in
+  for i = 0 to numbits e - 1 do
+    if bit e i = 1 then result := bn_mod (mul !result !b) m;
+    b := bn_mod (mul !b !b) m
+  done;
+  !result
+
+let of_bytes_be (s : string) : bn =
+  let acc = ref bzero in
+  for i = 0 to String.length s - 1 do
+    acc := add (mul !acc [| 256 |]) [| Char.code s.[i] |]
+  done;
+  !acc
+
+let div_small a d =
+  let la = Array.length a in
+  let q = Array.make la 0 and rem = ref 0 in
+  for i = la - 1 downto 0 do
+    let cur = (!rem lsl bits) lor a.(i) in
+    q.(i) <- cur / d; rem := cur mod d
+  done;
+  norm q
+
+let to_bytes_be (a : bn) (n : int) : string =
+  let b = Bytes.make n '\000' in
+  let cur = ref (norm a) in
+  for i = n - 1 downto 0 do
+    let q = div_small !cur 256 in
+    let r =
+      let d = sub !cur (mul q [| 256 |]) in
+      if is_zero d then 0 else d.(0)
+    in
+    Bytes.set b i (Char.chr r);
+    cur := q
+  done;
+  Bytes.unsafe_to_string b
+
+(* ---- Minimal DER reader (for SubjectPublicKeyInfo) ---- *)
+
+exception Der of string
+
+(* Returns (tag, content_start, content_len, next). *)
+let der_tlv s pos =
+  if pos + 2 > String.length s then raise (Der "short");
+  let tag = Char.code s.[pos] in
+  let l0 = Char.code s.[pos + 1] in
+  let len, hdr =
+    if l0 < 0x80 then l0, 2
+    else begin
+      let nb = l0 land 0x7f in
+      if pos + 2 + nb > String.length s then raise (Der "short len");
+      let v = ref 0 in
+      for i = 0 to nb - 1 do
+        v := (!v lsl 8) lor Char.code s.[pos + 2 + i]
+      done;
+      !v, 2 + nb
+    end
+  in
+  (tag, pos + hdr, len, pos + hdr + len)
+
+(* SPKI DER -> (n, e) as bignums. *)
+let parse_spki (der : string) : bn * bn =
+  let tag, c, _l, _ = der_tlv der 0 in
+  if tag <> 0x30 then raise (Der "spki: outer not SEQUENCE");
+  (* AlgorithmIdentifier SEQUENCE — skip. *)
+  let _, _, _, after_alg = der_tlv der c in
+  (* BIT STRING. *)
+  let bt, bc, bl, _ = der_tlv der after_alg in
+  if bt <> 0x03 then raise (Der "spki: expected BIT STRING");
+  (* First content byte = unused bits (must be 0). *)
+  let rpk_start = bc + 1 in
+  ignore bl;
+  let st, sc, _, _ = der_tlv der rpk_start in
+  if st <> 0x30 then raise (Der "spki: RSAPublicKey not SEQUENCE");
+  let nt, nc, nl, after_n = der_tlv der sc in
+  if nt <> 0x02 then raise (Der "spki: modulus not INTEGER");
+  let et, ec, el, _ = der_tlv der after_n in
+  if et <> 0x02 then raise (Der "spki: exponent not INTEGER");
+  let n = of_bytes_be (String.sub der nc nl) in
+  let e = of_bytes_be (String.sub der ec el) in
+  (n, e)
+
+(* SHA-256 DigestInfo DER prefix (RFC 8017 §9.2 note 1). *)
+let sha256_digestinfo_prefix =
+  "\x30\x31\x30\x0d\x06\x09\x60\x86\x48\x01\x65\x03\x04\x02\x01\x05\x00\x04\x20"
+
+let unhex h =
+  let n = String.length h / 2 in
+  let b = Bytes.create n in
+  for i = 0 to n - 1 do
+    Bytes.set b i (Char.chr (int_of_string ("0x" ^ String.sub h (2 * i) 2)))
+  done;
+  Bytes.unsafe_to_string b
+
+(* RSASSA-PKCS1-v1_5 verify with SHA-256. Total: any malformed
+   input yields false (caller wraps, but be defensive here too). *)
+let verify ~spki ~msg ~sig_ : bool =
+  try
+    let n, e = parse_spki spki in
+    let k = (numbits n + 7) / 8 in
+    if String.length sig_ <> k then false
+    else begin
+      let s = of_bytes_be sig_ in
+      if cmp s n >= 0 then false
+      else begin
+        let m = powmod s e n in
+        let em = to_bytes_be m k in
+        (* EM = 0x00 01 FF..FF 00 || DigestInfo || H *)
+        let h = unhex (Sx_sha2.sha256_hex msg) in
+        let t = sha256_digestinfo_prefix ^ h in
+        let tlen = String.length t in
+        if k < tlen + 11 then false
+        else begin
+          let ok = ref (em.[0] = '\x00' && em.[1] = '\x01') in
+          let ps_end = k - tlen - 1 in
+          for i = 2 to ps_end - 1 do
+            if em.[i] <> '\xff' then ok := false
+          done;
+          if em.[ps_end] <> '\x00' then ok := false;
+          if String.sub em (ps_end + 1) tlen <> t then ok := false;
+          !ok
+        end
+      end
+    end
+  with _ -> false

hosts/ocaml/lib/sx_sha2.ml

@@ -0,0 +1,212 @@
+(** SHA-2 (SHA-256, SHA-512) — pure OCaml, WASM-safe.
+
+    No C stubs, no external deps. Used by the fed-sx host primitives
+    [crypto-sha256] / [crypto-sha512]. Reference: FIPS 180-4. *)
+
+(* ---- SHA-256 (FIPS 180-4 §6.2). 32-bit words held in native int,
+   masked to 32 bits after every arithmetic op. ---- *)
+
+let mask32 = 0xFFFFFFFF
+
+let k256 = [|
+  0x428a2f98; 0x71374491; 0xb5c0fbcf; 0xe9b5dba5;
+  0x3956c25b; 0x59f111f1; 0x923f82a4; 0xab1c5ed5;
+  0xd807aa98; 0x12835b01; 0x243185be; 0x550c7dc3;
+  0x72be5d74; 0x80deb1fe; 0x9bdc06a7; 0xc19bf174;
+  0xe49b69c1; 0xefbe4786; 0x0fc19dc6; 0x240ca1cc;
+  0x2de92c6f; 0x4a7484aa; 0x5cb0a9dc; 0x76f988da;
+  0x983e5152; 0xa831c66d; 0xb00327c8; 0xbf597fc7;
+  0xc6e00bf3; 0xd5a79147; 0x06ca6351; 0x14292967;
+  0x27b70a85; 0x2e1b2138; 0x4d2c6dfc; 0x53380d13;
+  0x650a7354; 0x766a0abb; 0x81c2c92e; 0x92722c85;
+  0xa2bfe8a1; 0xa81a664b; 0xc24b8b70; 0xc76c51a3;
+  0xd192e819; 0xd6990624; 0xf40e3585; 0x106aa070;
+  0x19a4c116; 0x1e376c08; 0x2748774c; 0x34b0bcb5;
+  0x391c0cb3; 0x4ed8aa4a; 0x5b9cca4f; 0x682e6ff3;
+  0x748f82ee; 0x78a5636f; 0x84c87814; 0x8cc70208;
+  0x90befffa; 0xa4506ceb; 0xbef9a3f7; 0xc67178f2 |]
+
+let rotr32 x n = ((x lsr n) lor (x lsl (32 - n))) land mask32
+
+let sha256_hex (msg : string) : string =
+  let h = [| 0x6a09e667; 0xbb67ae85; 0x3c6ef372; 0xa54ff53a;
+             0x510e527f; 0x9b05688c; 0x1f83d9ab; 0x5be0cd19 |] in
+  let len = String.length msg in
+  (* Padded length: multiple of 64 bytes. *)
+  let bitlen = len * 8 in
+  let padlen =
+    let r = (len + 1) mod 64 in
+    if r <= 56 then 56 - r else 120 - r
+  in
+  let total = len + 1 + padlen + 8 in
+  let buf = Bytes.make total '\000' in
+  Bytes.blit_string msg 0 buf 0 len;
+  Bytes.set buf len '\x80';
+  (* 64-bit big-endian bit length (we cap at OCaml int range). *)
+  for i = 0 to 7 do
+    Bytes.set buf (total - 1 - i)
+      (Char.chr ((bitlen lsr (8 * i)) land 0xFF))
+  done;
+  let w = Array.make 64 0 in
+  let nblocks = total / 64 in
+  for b = 0 to nblocks - 1 do
+    let base = b * 64 in
+    for t = 0 to 15 do
+      let o = base + t * 4 in
+      w.(t) <-
+        (Char.code (Bytes.get buf o) lsl 24)
+        lor (Char.code (Bytes.get buf (o + 1)) lsl 16)
+        lor (Char.code (Bytes.get buf (o + 2)) lsl 8)
+        lor (Char.code (Bytes.get buf (o + 3)))
+    done;
+    for t = 16 to 63 do
+      let s0 =
+        (rotr32 w.(t - 15) 7) lxor (rotr32 w.(t - 15) 18)
+        lxor (w.(t - 15) lsr 3) in
+      let s1 =
+        (rotr32 w.(t - 2) 17) lxor (rotr32 w.(t - 2) 19)
+        lxor (w.(t - 2) lsr 10) in
+      w.(t) <- (w.(t - 16) + s0 + w.(t - 7) + s1) land mask32
+    done;
+    let a = ref h.(0) and bb = ref h.(1) and c = ref h.(2)
+    and d = ref h.(3) and e = ref h.(4) and f = ref h.(5)
+    and g = ref h.(6) and hh = ref h.(7) in
+    for t = 0 to 63 do
+      let s1 =
+        (rotr32 !e 6) lxor (rotr32 !e 11) lxor (rotr32 !e 25) in
+      let ch = (!e land !f) lxor ((lnot !e land mask32) land !g) in
+      let t1 = (!hh + s1 + ch + k256.(t) + w.(t)) land mask32 in
+      let s0 =
+        (rotr32 !a 2) lxor (rotr32 !a 13) lxor (rotr32 !a 22) in
+      let maj = (!a land !bb) lxor (!a land !c) lxor (!bb land !c) in
+      let t2 = (s0 + maj) land mask32 in
+      hh := !g; g := !f; f := !e;
+      e := (!d + t1) land mask32;
+      d := !c; c := !bb; bb := !a;
+      a := (t1 + t2) land mask32
+    done;
+    h.(0) <- (h.(0) + !a) land mask32;
+    h.(1) <- (h.(1) + !bb) land mask32;
+    h.(2) <- (h.(2) + !c) land mask32;
+    h.(3) <- (h.(3) + !d) land mask32;
+    h.(4) <- (h.(4) + !e) land mask32;
+    h.(5) <- (h.(5) + !f) land mask32;
+    h.(6) <- (h.(6) + !g) land mask32;
+    h.(7) <- (h.(7) + !hh) land mask32
+  done;
+  let out = Buffer.create 64 in
+  Array.iter (fun x -> Buffer.add_string out (Printf.sprintf "%08x" x)) h;
+  Buffer.contents out
+
+(* ---- SHA-512 (FIPS 180-4 §6.4). 64-bit words via Int64.
+   128-bit length append; we only support messages whose bit length
+   fits in 64 bits (high word is always zero). ---- *)
+
+let k512 = [|
+  0x428a2f98d728ae22L; 0x7137449123ef65cdL; 0xb5c0fbcfec4d3b2fL;
+  0xe9b5dba58189dbbcL; 0x3956c25bf348b538L; 0x59f111f1b605d019L;
+  0x923f82a4af194f9bL; 0xab1c5ed5da6d8118L; 0xd807aa98a3030242L;
+  0x12835b0145706fbeL; 0x243185be4ee4b28cL; 0x550c7dc3d5ffb4e2L;
+  0x72be5d74f27b896fL; 0x80deb1fe3b1696b1L; 0x9bdc06a725c71235L;
+  0xc19bf174cf692694L; 0xe49b69c19ef14ad2L; 0xefbe4786384f25e3L;
+  0x0fc19dc68b8cd5b5L; 0x240ca1cc77ac9c65L; 0x2de92c6f592b0275L;
+  0x4a7484aa6ea6e483L; 0x5cb0a9dcbd41fbd4L; 0x76f988da831153b5L;
+  0x983e5152ee66dfabL; 0xa831c66d2db43210L; 0xb00327c898fb213fL;
+  0xbf597fc7beef0ee4L; 0xc6e00bf33da88fc2L; 0xd5a79147930aa725L;
+  0x06ca6351e003826fL; 0x142929670a0e6e70L; 0x27b70a8546d22ffcL;
+  0x2e1b21385c26c926L; 0x4d2c6dfc5ac42aedL; 0x53380d139d95b3dfL;
+  0x650a73548baf63deL; 0x766a0abb3c77b2a8L; 0x81c2c92e47edaee6L;
+  0x92722c851482353bL; 0xa2bfe8a14cf10364L; 0xa81a664bbc423001L;
+  0xc24b8b70d0f89791L; 0xc76c51a30654be30L; 0xd192e819d6ef5218L;
+  0xd69906245565a910L; 0xf40e35855771202aL; 0x106aa07032bbd1b8L;
+  0x19a4c116b8d2d0c8L; 0x1e376c085141ab53L; 0x2748774cdf8eeb99L;
+  0x34b0bcb5e19b48a8L; 0x391c0cb3c5c95a63L; 0x4ed8aa4ae3418acbL;
+  0x5b9cca4f7763e373L; 0x682e6ff3d6b2b8a3L; 0x748f82ee5defb2fcL;
+  0x78a5636f43172f60L; 0x84c87814a1f0ab72L; 0x8cc702081a6439ecL;
+  0x90befffa23631e28L; 0xa4506cebde82bde9L; 0xbef9a3f7b2c67915L;
+  0xc67178f2e372532bL; 0xca273eceea26619cL; 0xd186b8c721c0c207L;
+  0xeada7dd6cde0eb1eL; 0xf57d4f7fee6ed178L; 0x06f067aa72176fbaL;
+  0x0a637dc5a2c898a6L; 0x113f9804bef90daeL; 0x1b710b35131c471bL;
+  0x28db77f523047d84L; 0x32caab7b40c72493L; 0x3c9ebe0a15c9bebcL;
+  0x431d67c49c100d4cL; 0x4cc5d4becb3e42b6L; 0x597f299cfc657e2aL;
+  0x5fcb6fab3ad6faecL; 0x6c44198c4a475817L |]
+
+let ( &: ) = Int64.logand
+let ( |: ) = Int64.logor
+let ( ^: ) = Int64.logxor
+let ( +: ) = Int64.add
+let lnot64 = Int64.lognot
+
+let rotr64 x n =
+  (Int64.shift_right_logical x n) |: (Int64.shift_left x (64 - n))
+
+let sha512_hex (msg : string) : string =
+  let h = [| 0x6a09e667f3bcc908L; 0xbb67ae8584caa73bL;
+             0x3c6ef372fe94f82bL; 0xa54ff53a5f1d36f1L;
+             0x510e527fade682d1L; 0x9b05688c2b3e6c1fL;
+             0x1f83d9abfb41bd6bL; 0x5be0cd19137e2179L |] in
+  let len = String.length msg in
+  let bitlen = len * 8 in
+  (* Pad to a multiple of 128 bytes; 16-byte big-endian length. *)
+  let padlen =
+    let r = (len + 1) mod 128 in
+    if r <= 112 then 112 - r else 240 - r
+  in
+  let total = len + 1 + padlen + 16 in
+  let buf = Bytes.make total '\000' in
+  Bytes.blit_string msg 0 buf 0 len;
+  Bytes.set buf len '\x80';
+  for i = 0 to 7 do
+    Bytes.set buf (total - 1 - i)
+      (Char.chr ((bitlen lsr (8 * i)) land 0xFF))
+  done;
+  let w = Array.make 80 0L in
+  let nblocks = total / 128 in
+  for b = 0 to nblocks - 1 do
+    let base = b * 128 in
+    for t = 0 to 15 do
+      let o = base + t * 8 in
+      let v = ref 0L in
+      for j = 0 to 7 do
+        v := Int64.logor (Int64.shift_left !v 8)
+               (Int64.of_int (Char.code (Bytes.get buf (o + j))))
+      done;
+      w.(t) <- !v
+    done;
+    for t = 16 to 79 do
+      let s0 =
+        (rotr64 w.(t - 15) 1) ^: (rotr64 w.(t - 15) 8)
+        ^: (Int64.shift_right_logical w.(t - 15) 7) in
+      let s1 =
+        (rotr64 w.(t - 2) 19) ^: (rotr64 w.(t - 2) 61)
+        ^: (Int64.shift_right_logical w.(t - 2) 6) in
+      w.(t) <- w.(t - 16) +: s0 +: w.(t - 7) +: s1
+    done;
+    let a = ref h.(0) and bb = ref h.(1) and c = ref h.(2)
+    and d = ref h.(3) and e = ref h.(4) and f = ref h.(5)
+    and g = ref h.(6) and hh = ref h.(7) in
+    for t = 0 to 79 do
+      let s1 = (rotr64 !e 14) ^: (rotr64 !e 18) ^: (rotr64 !e 41) in
+      let ch = (!e &: !f) ^: ((lnot64 !e) &: !g) in
+      let t1 = !hh +: s1 +: ch +: k512.(t) +: w.(t) in
+      let s0 = (rotr64 !a 28) ^: (rotr64 !a 34) ^: (rotr64 !a 39) in
+      let maj = (!a &: !bb) ^: (!a &: !c) ^: (!bb &: !c) in
+      let t2 = s0 +: maj in
+      hh := !g; g := !f; f := !e;
+      e := !d +: t1;
+      d := !c; c := !bb; bb := !a;
+      a := t1 +: t2
+    done;
+    h.(0) <- h.(0) +: !a;
+    h.(1) <- h.(1) +: !bb;
+    h.(2) <- h.(2) +: !c;
+    h.(3) <- h.(3) +: !d;
+    h.(4) <- h.(4) +: !e;
+    h.(5) <- h.(5) +: !f;
+    h.(6) <- h.(6) +: !g;
+    h.(7) <- h.(7) +: !hh
+  done;
+  let out = Buffer.create 128 in
+  Array.iter
+    (fun x -> Buffer.add_string out (Printf.sprintf "%016Lx" x)) h;
+  Buffer.contents out

hosts/ocaml/lib/sx_sha3.ml

@@ -0,0 +1,107 @@
+(** SHA-3 (SHA3-256) — pure OCaml, WASM-safe.
+
+    Keccak-f[1600] permutation + SHA-3 multi-rate padding (domain byte
+    0x06, NOT the legacy Keccak 0x01). Reference: FIPS 202. No deps. *)
+
+let ( ^: ) = Int64.logxor
+let ( &: ) = Int64.logand
+let lnot64 = Int64.lognot
+
+let rotl64 x n =
+  if n = 0 then x
+  else
+    Int64.logor (Int64.shift_left x n) (Int64.shift_right_logical x (64 - n))
+
+(* FIPS 202 Table 2 — ρ rotation offsets, indexed lane = x + 5*y. *)
+let rho = [|
+   0;  1; 62; 28; 27;
+  36; 44;  6; 55; 20;
+   3; 10; 43; 25; 39;
+  41; 45; 15; 21;  8;
+  18;  2; 61; 56; 14 |]
+
+(* FIPS 202 §3.2.5 — round constants RC[0..23] for ι. *)
+let rc = [|
+  0x0000000000000001L; 0x0000000000008082L; 0x800000000000808aL;
+  0x8000000080008000L; 0x000000000000808bL; 0x0000000080000001L;
+  0x8000000080008081L; 0x8000000000008009L; 0x000000000000008aL;
+  0x0000000000000088L; 0x0000000080008009L; 0x000000008000000aL;
+  0x000000008000808bL; 0x800000000000008bL; 0x8000000000008089L;
+  0x8000000000008003L; 0x8000000000008002L; 0x8000000000000080L;
+  0x000000000000800aL; 0x800000008000000aL; 0x8000000080008081L;
+  0x8000000000008080L; 0x0000000080000001L; 0x8000000080008008L |]
+
+let keccak_f (a : int64 array) : unit =
+  let c = Array.make 5 0L and d = Array.make 5 0L in
+  let b = Array.make 25 0L in
+  for round = 0 to 23 do
+    (* θ *)
+    for x = 0 to 4 do
+      c.(x) <- a.(x) ^: a.(x + 5) ^: a.(x + 10)
+               ^: a.(x + 15) ^: a.(x + 20)
+    done;
+    for x = 0 to 4 do
+      d.(x) <- c.((x + 4) mod 5) ^: (rotl64 c.((x + 1) mod 5) 1)
+    done;
+    for x = 0 to 4 do
+      for y = 0 to 4 do
+        a.(x + 5 * y) <- a.(x + 5 * y) ^: d.(x)
+      done
+    done;
+    (* ρ and π: B[y, 2x+3y] = rotl(A[x,y], rho[x,y]) *)
+    for x = 0 to 4 do
+      for y = 0 to 4 do
+        let nx = y and ny = (2 * x + 3 * y) mod 5 in
+        b.(nx + 5 * ny) <- rotl64 a.(x + 5 * y) rho.(x + 5 * y)
+      done
+    done;
+    (* χ *)
+    for y = 0 to 4 do
+      for x = 0 to 4 do
+        a.(x + 5 * y) <-
+          b.(x + 5 * y)
+          ^: ((lnot64 b.((x + 1) mod 5 + 5 * y))
+              &: b.((x + 2) mod 5 + 5 * y))
+      done
+    done;
+    (* ι *)
+    a.(0) <- a.(0) ^: rc.(round)
+  done
+
+let sha3_256_hex (msg : string) : string =
+  let rate = 136 (* bytes: (1600 - 2*256) / 8 *) in
+  let len = String.length msg in
+  (* pad10*1 with SHA-3 domain byte 0x06; last byte ORed with 0x80. *)
+  let q = rate - (len mod rate) in
+  let padded = Bytes.make (len + q) '\000' in
+  Bytes.blit_string msg 0 padded 0 len;
+  if q = 1 then
+    Bytes.set padded len '\x86'
+  else begin
+    Bytes.set padded len '\x06';
+    Bytes.set padded (len + q - 1) '\x80'
+  end;
+  let total = Bytes.length padded in
+  let a = Array.make 25 0L in
+  let nblocks = total / rate in
+  for blk = 0 to nblocks - 1 do
+    let base = blk * rate in
+    (* Absorb: XOR rate bytes into the state, little-endian lanes. *)
+    for j = 0 to rate - 1 do
+      let lane = j / 8 and sh = (j mod 8) * 8 in
+      let byte = Int64.of_int (Char.code (Bytes.get padded (base + j))) in
+      a.(lane) <- a.(lane) ^: (Int64.shift_left byte sh)
+    done;
+    keccak_f a
+  done;
+  (* Squeeze 32 bytes (fits in the first 4 lanes; rate > 32). *)
+  let out = Buffer.create 64 in
+  for j = 0 to 31 do
+    let lane = j / 8 and sh = (j mod 8) * 8 in
+    let byte =
+      Int64.to_int
+        (Int64.logand (Int64.shift_right_logical a.(lane) sh) 0xFFL)
+    in
+    Buffer.add_string out (Printf.sprintf "%02x" byte)
+  done;
+  Buffer.contents out

hosts/ocaml/lib/sx_vm.ml

@@ -44,6 +44,11 @@ type vm = {
     ip past OP_PERFORM, stack ready for a result push). *)
 exception VmSuspended of value * vm
 
+(** Raised by the extension dispatch fallthrough when an opcode in the
+    extension range (≥ 200) is encountered with no handler registered.
+    Carries the offending opcode id. See plans/sx-vm-opcode-extension.md. *)
+exception Invalid_opcode of int
+
 (* Register the VM suspension converter so sx_runtime.sx_apply_cek can
    catch VmSuspended and convert it to CekPerformRequest without a
    direct dependency on this module. *)
@@ -57,6 +62,21 @@ let () = Sx_types._convert_vm_suspension := (fun exn ->
 let jit_compile_ref : (lambda -> (string, value) Hashtbl.t -> vm_closure option) ref =
   ref (fun _ _ -> None)
 
+(** Forward reference for extension opcode dispatch — Phase B installs the
+    real registry's dispatch function here at module init. Until then, any
+    opcode in the extension range raises [Invalid_opcode]. Same forward-ref
+    pattern as [jit_compile_ref] above; keeps [Sx_vm_extensions] free to
+    depend on [Sx_vm]'s [vm] / [frame] types without a cycle. *)
+let extension_dispatch_ref : (int -> vm -> frame -> unit) ref =
+  ref (fun op _vm _frame -> raise (Invalid_opcode op))
+
+(** Forward reference for extension opcode → name lookup, used by
+    [opcode_name] / [disassemble] for human-readable disassembly.  The
+    registry installs a real lookup at module init; default returns
+    [None] (then [opcode_name] falls back to "UNKNOWN_n"). *)
+let extension_opcode_name_ref : (int -> string option) ref =
+  ref (fun _ -> None)
+
 (* JIT threshold and counters live in Sx_types so primitives can read them
    without creating a sx_primitives → sx_vm dependency cycle. *)
 
@@ -875,6 +895,15 @@ and run vm =
           let request = pop vm in
           raise (VmSuspended (request, vm))
 
+        (* ---- Extension dispatch fallthrough ----
+           Opcode partition (see plans/sx-vm-opcode-extension.md):
+             0       reserved / NOP
+             1-199   core opcodes (current ceiling 175 = OP_DEC)
+             200-247 extension opcodes (registered via Sx_vm_extensions)
+             248-255 reserved for future expansion / multi-byte
+           Any opcode ≥ 200 routes through the extension registry. *)
+        | op when op >= 200 -> !extension_dispatch_ref op vm frame
+
         | opcode ->
           raise (Eval_error (Printf.sprintf "VM: unknown opcode %d at ip=%d"
                                opcode (frame.ip - 1)))
@@ -1027,6 +1056,62 @@ let _jit_is_broken_name n =
   || n = "hs-repeat-while" || n = "hs-repeat-until"
   || n = "hs-for-each" || n = "hs-put!"
 
+(** Scan bytecode for any extension opcode (≥ 200, the registry's
+    [Sx_vm_extensions.extension_min]). Walks operand bytes correctly
+    so values that happen to be ≥200 (e.g. a CONST u16 index pointing
+    into a large pool) do not trigger false positives. CLOSURE's
+    dynamic upvalue descriptors are read from the constant pool entry
+    at the same index it pushes.
+
+    Used by [jit_compile_lambda] (Phase E of the opcode-extension
+    plan): a lambda whose compiled body contains any extension opcode
+    is routed through interpretation rather than JIT.  Extensions
+    interpret their opcodes via the registry; the JIT does not
+    currently know how to compile them.
+
+    Operand-size logic mirrors [opcode_operand_size] (which is defined
+    later, in the disassembly section); inlined here so this helper can
+    sit before [jit_compile_lambda] in the file. *)
+let bytecode_uses_extension_opcodes (bc : int array) (consts : value array) =
+  let core_operand_size = function
+    | 1 | 20 | 21 | 64 | 65 | 128 -> 2  (* u16 *)
+    | 16 | 17 | 18 | 19 | 48 | 49 | 144 -> 1  (* u8 *)
+    | 32 | 33 | 34 | 35 -> 2  (* i16 *)
+    | 52 -> 3  (* CALL_PRIM: u16 + u8 *)
+    | _ -> 0
+  in
+  let len = Array.length bc in
+  let ip = ref 0 in
+  let found = ref false in
+  while not !found && !ip < len do
+    let op = bc.(!ip) in
+    if op >= 200 then found := true
+    else begin
+      ip := !ip + 1;
+      let extra = match op with
+        | 51 (* CLOSURE *) when !ip + 1 < len ->
+          let lo = bc.(!ip) in
+          let hi = bc.(!ip + 1) in
+          let idx = lo lor (hi lsl 8) in
+          let uv_count =
+            if idx < Array.length consts then
+              (match consts.(idx) with
+               | Dict d ->
+                 (match Hashtbl.find_opt d "upvalue-count" with
+                  | Some (Integer n) -> n
+                  | Some (Number n) -> int_of_float n
+                  | _ -> 0)
+               | _ -> 0)
+            else 0
+          in
+          2 + uv_count * 2
+        | _ -> core_operand_size op
+      in
+      ip := !ip + extra
+    end
+  done;
+  !found
+
 let jit_compile_lambda (l : lambda) globals =
   let fn_name = match l.l_name with Some n -> n | None -> "<anon>" in
   if !_jit_compiling then (
@@ -1089,8 +1174,18 @@ let jit_compile_lambda (l : lambda) globals =
         if idx < Array.length outer_code.vc_constants then
           let inner_val = outer_code.vc_constants.(idx) in
           let code = code_from_value inner_val in
-          Some { vm_code = code; vm_upvalues = [||];
+          (* Phase E: if the inner lambda's bytecode contains any
-                 vm_name = l.l_name; vm_env_ref = effective_globals; vm_closure_env = Some l.l_closure }
+             extension opcode (≥200), skip JIT and let the lambda run
+             interpreted via CEK. Extension opcodes dispatch correctly
+             through the VM's registry fallthrough, but the JIT has no
+             knowledge of them and shouldn't claim ownership. *)
+          if bytecode_uses_extension_opcodes code.vc_bytecode code.vc_constants then begin
+            Printf.eprintf "[jit] SKIP %s: bytecode uses extension opcodes (interpret-only in v1)\n%!"
+              fn_name;
+            None
+          end else
+            Some { vm_code = code; vm_upvalues = [||];
+                   vm_name = l.l_name; vm_env_ref = effective_globals; vm_closure_env = Some l.l_closure }
         else begin
           Printf.eprintf "[jit] FAIL %s: closure index %d out of bounds (pool=%d)\n%!"
             fn_name idx (Array.length outer_code.vc_constants);
@@ -1200,7 +1295,12 @@ let opcode_name = function
   | 164 -> "EQ" | 165 -> "LT" | 166 -> "GT" | 167 -> "NOT"
   | 168 -> "LEN" | 169 -> "FIRST" | 170 -> "REST" | 171 -> "NTH"
   | 172 -> "CONS" | 173 -> "NEG" | 174 -> "INC" | 175 -> "DEC"
-  | n -> Printf.sprintf "UNKNOWN_%d" n
+  | n ->
+    (* Extension opcodes (≥200) get their human-readable name from the
+       registry; defaults to UNKNOWN_n if the extension isn't loaded. *)
+    (match !extension_opcode_name_ref n with
+     | Some name -> name
+     | None -> Printf.sprintf "UNKNOWN_%d" n)
 
 (** Number of extra operand bytes consumed by each opcode.
     Returns (format, total_bytes) where format describes the operand types. *)

hosts/ocaml/lib/sx_vm_extension.ml

@@ -0,0 +1,48 @@
+(** {1 VM extension interface}
+
+    Type definitions for VM bytecode extensions. See
+    [plans/sx-vm-opcode-extension.md].
+
+    An extension is a first-class module of type [EXTENSION]: it has a
+    stable [name], an [init] that returns its private state, and an
+    [opcodes] function that lists the opcodes it provides.
+
+    Opcode handlers receive the live [vm] and the active [frame]. They
+    read operands via [Sx_vm.read_u8] / [read_u16], manipulate the stack
+    via [push] / [pop] / [peek], and update the frame's [ip] as needed. *)
+
+(** A handler for an extension opcode. Reads operands from bytecode,
+    manipulates the VM stack, updates the frame's instruction pointer.
+    May raise exceptions (which propagate via the existing VM error path). *)
+type handler = Sx_vm.vm -> Sx_vm.frame -> unit
+
+(** State an extension carries alongside the VM. Opaque to the VM core;
+    extensions extend this with their own constructor and cast as needed.
+
+    Extensible variant — extensions add cases:
+    {[
+      type Sx_vm_extension.extension_state +=
+        | ErlangState of erlang_scheduler
+    ]} *)
+type extension_state = ..
+
+(** An extension is a first-class module of this signature. *)
+module type EXTENSION = sig
+  (** Stable name for this extension (e.g. ["erlang"], ["guest_vm"]).
+      Used as the lookup key in the registry and as the prefix for opcode
+      names ([erlang.OP_PATTERN_TUPLE_2] etc). *)
+  val name : string
+
+  (** Initialize per-instance state. Called once when [register] is
+      invoked on this extension. *)
+  val init : unit -> extension_state
+
+  (** Opcodes this extension provides. Each is
+      [(opcode_id, opcode_name, handler)].
+
+      [opcode_id] must be in the range 200-247 (the extension partition;
+      see the partition comment at the top of [Sx_vm]'s dispatch loop).
+      Conflicts with already-registered opcodes cause [register] to
+      fail. *)
+  val opcodes : extension_state -> (int * string * handler) list
+end

hosts/ocaml/lib/sx_vm_extensions.ml

@@ -0,0 +1,120 @@
+(** {1 VM extension registry}
+
+    Holds the live registry of extension opcodes and installs the
+    [dispatch] function into [Sx_vm.extension_dispatch_ref] at module
+    init time, replacing Phase A's stub.
+
+    See [plans/sx-vm-opcode-extension.md] and [Sx_vm_extension] for the
+    extension interface. *)
+
+open Sx_vm_extension
+
+(** The opcode range an extension is allowed to claim.
+    Mirrors the partition comment in [Sx_vm]. *)
+let extension_min = 200
+let extension_max = 247
+
+(** opcode_id → handler *)
+let by_id : (int, handler) Hashtbl.t = Hashtbl.create 64
+
+(** opcode_name → opcode_id *)
+let by_name : (string, int) Hashtbl.t = Hashtbl.create 64
+
+(** opcode_id → opcode_name (reverse of [by_name]; used by
+    [Sx_vm.opcode_name] for disassembly). *)
+let name_of_id_table : (int, string) Hashtbl.t = Hashtbl.create 64
+
+(** extension_name → state *)
+let states : (string, extension_state) Hashtbl.t = Hashtbl.create 8
+
+(** Registered extension names, newest first. *)
+let extensions : string list ref = ref []
+
+(** Dispatch an extension opcode to its registered handler. Raises
+    [Sx_vm.Invalid_opcode] if no handler is registered for [op]. *)
+let dispatch op vm frame =
+  match Hashtbl.find_opt by_id op with
+  | Some handler -> handler vm frame
+  | None -> raise (Sx_vm.Invalid_opcode op)
+
+(** Register an extension. Fails if the extension name is already
+    registered, or if any opcode_id is outside the extension range or
+    collides with an already-registered opcode. *)
+let register (m : (module EXTENSION)) =
+  let module M = (val m) in
+  if Hashtbl.mem states M.name then
+    failwith (Printf.sprintf
+      "Sx_vm_extensions: extension %S already registered" M.name);
+  let st = M.init () in
+  let ops = M.opcodes st in
+  List.iter (fun (id, opname, _h) ->
+    if id < extension_min || id > extension_max then
+      failwith (Printf.sprintf
+        "Sx_vm_extensions: opcode %d (%s) outside extension range %d-%d"
+        id opname extension_min extension_max);
+    if Hashtbl.mem by_id id then
+      failwith (Printf.sprintf
+        "Sx_vm_extensions: opcode %d (%s) already registered" id opname);
+    if Hashtbl.mem by_name opname then
+      failwith (Printf.sprintf
+        "Sx_vm_extensions: opcode name %S already registered" opname)
+  ) ops;
+  Hashtbl.add states M.name st;
+  List.iter (fun (id, opname, h) ->
+    Hashtbl.add by_id id h;
+    Hashtbl.add by_name opname id;
+    Hashtbl.add name_of_id_table id opname
+  ) ops;
+  extensions := M.name :: !extensions
+
+(** Look up the opcode_id for an opcode_name. Returns [None] if no
+    extension provides that opcode. *)
+let id_of_name name = Hashtbl.find_opt by_name name
+
+(** Look up the opcode_name for an opcode_id. Returns [None] if no
+    extension provides that opcode. Used by disassembly. *)
+let name_of_id id = Hashtbl.find_opt name_of_id_table id
+
+(** Look up the state of an extension by name. Returns [None] if the
+    extension is not registered. *)
+let state_of_extension name = Hashtbl.find_opt states name
+
+(** Names of all registered extensions, newest first. *)
+let registered_extensions () = !extensions
+
+(** Test-only: clear the registry. Used by unit tests to isolate
+    extensions between test cases. The dispatch_ref is left in place. *)
+let _reset_for_tests () =
+  Hashtbl.clear by_id;
+  Hashtbl.clear by_name;
+  Hashtbl.clear name_of_id_table;
+  Hashtbl.clear states;
+  extensions := []
+
+(** Install our [dispatch] into [Sx_vm.extension_dispatch_ref] and our
+    [name_of_id] into [Sx_vm.extension_opcode_name_ref], replacing
+    the Phase A stubs. Idempotent. Called automatically at module init. *)
+let install_dispatch () =
+  Sx_vm.extension_dispatch_ref := dispatch;
+  Sx_vm.extension_opcode_name_ref := name_of_id
+
+let () = install_dispatch ()
+
+(** Compiler-side opcode lookup: register the [extension-opcode-id]
+    primitive. Compilers ([lib/compiler.sx]) call this to emit
+    extension opcodes by name. Returns [Integer id] when registered,
+    [Nil] otherwise — so missing extensions degrade to a fallback
+    rather than failure. *)
+let () =
+  Sx_primitives.register "extension-opcode-id" (fun args ->
+    match args with
+    | [Sx_types.String name] ->
+      (match id_of_name name with
+       | Some id -> Sx_types.Integer id
+       | None -> Sx_types.Nil)
+    | [Sx_types.Symbol name] ->
+      (match id_of_name name with
+       | Some id -> Sx_types.Integer id
+       | None -> Sx_types.Nil)
+    | _ -> raise (Sx_types.Eval_error
+        "extension-opcode-id: expected one string or symbol"))

lib/datalog/scoreboard.json

@@ -16,5 +16,5 @@
     {"name":"magic","passed":37,"failed":0,"total":37},
     {"name":"demo","passed":21,"failed":0,"total":21}
   ],
-  "generated": "2026-05-11T09:40:12+00:00"
+  "generated": "2026-05-14T20:30:05+00:00"
 }

lib/erlang/bench_ring_results.md

@@ -33,3 +33,54 @@ least: persistent (path-copying) envs, an inline scheduler that
 doesn't call/cc on the common path (msg-already-in-mailbox), and a
 linked-list mailbox. None of those are in scope for the Phase 3
 checkbox — captured here as the floor we're starting from.
+
+## Phase 9 status (2026-05-14)
+
+Specialized opcodes 9b–9f landed as **stub dispatchers** in
+`lib/erlang/vm/dispatcher.sx`: `OP_PATTERN_TUPLE/LIST/BINARY`,
+`OP_PERFORM/HANDLE`, `OP_RECEIVE_SCAN`, `OP_SPAWN/SEND`, and ten
+`OP_BIF_*` hot dispatch entries. Each opcode's handler is a thin
+wrapper over the existing `er-match-*` / `er-bif-*` / runtime impls,
+so **the perf numbers above are unchanged** — same per-hop cost, same
+scheduler. The stubs exist to nail down opcode IDs, operand contracts,
+and tests against `er-match!` parity *before* 9a (the OCaml
+opcode-extension mechanism in `hosts/ocaml/evaluator/`) lands.
+
+When 9a integrates and the bytecode compiler can emit these opcodes
+at hot call sites, the real speedup story (~3000× ring throughput,
+~1000× spawn) starts. Until then this file documents the
+pre-integration ceiling. 72 vm-suite tests guard the stub correctness;
+full conformance is **709/709** with the stub infrastructure loaded.
+
+## Phase 9g — post-integration bench (2026-05-15)
+
+9a (vm-ext mechanism), 9h (`erlang_ext.ml` registering `erlang.OP_*`
+ids 222-239), and 9i (SX dispatcher consulting `extension-opcode-id`)
+are now integrated and built into `hosts/ocaml/_build/default/bin/sx_server.exe`.
+Re-ran the ring ladder on that binary:
+
+| N (processes) | Hops | Wall-clock | Throughput |
+|---|---|---|---|
+| 10 | 10 | 938ms | 11 hops/s |
+| 100 | 100 | 2772ms | 36 hops/s |
+| 500 | 500 | 14190ms | 35 hops/s |
+| 1000 | 1000 | 31814ms | 31 hops/s |
+
+**Numbers are unchanged from the pre-integration baseline** — and that
+is the expected, correct result. The opcode handlers (both the SX stub
+dispatcher and the OCaml `erlang_ext` module) wrap the existing
+`er-match-*` / `er-bif-*` / scheduler implementations 1-to-1, and the
+**bytecode compiler does not yet emit `erlang.OP_*` opcodes**, so every
+hop still goes through the general CEK path exactly as before. The
+unchanged numbers therefore double as a no-regression check: the full
+extension wiring (cherry-picked vm-ext A-E + force-link + erlang_ext +
+SX bridge) added zero per-hop cost. Conformance **715/715** on this
+binary.
+
+The ~3000×/~1000× targets remain gated on a **future phase (Phase 10 —
+bytecode emission)**: teach `lib/compiler.sx` (or the Erlang
+transpiler) to emit `erlang.OP_PATTERN_TUPLE` etc. at hot call sites,
+then give `erlang_ext.ml` real register-machine handlers instead of the
+current honest not-wired raise. That is a substantial standalone phase,
+tracked in `plans/erlang-on-sx.md`. 9g's deliverable — *honest
+measurement + recorded numbers on the integrated binary* — is complete.

lib/erlang/conformance.sh

@@ -36,6 +36,9 @@ SUITES=(
   "bank|er-bank-test-pass|er-bank-test-count"
   "echo|er-echo-test-pass|er-echo-test-count"
   "fib|er-fib-test-pass|er-fib-test-count"
+  "ffi|er-ffi-test-pass|er-ffi-test-count"
+  "vm|er-vm-test-pass|er-vm-test-count"
+  "send_after|er-sa-test-pass|er-sa-test-count"
 )
 
 cat > "$TMPFILE" << 'EPOCHS'
@@ -56,6 +59,10 @@ cat > "$TMPFILE" << 'EPOCHS'
 (load "lib/erlang/tests/programs/bank.sx")
 (load "lib/erlang/tests/programs/echo.sx")
 (load "lib/erlang/tests/programs/fib_server.sx")
+(load "lib/erlang/vm/dispatcher.sx")
+(load "lib/erlang/tests/ffi.sx")
+(load "lib/erlang/tests/vm.sx")
+(load "lib/erlang/tests/send_after.sx")
 (epoch 100)
 (eval "(list er-test-pass er-test-count)")
 (epoch 101)
@@ -74,6 +81,12 @@ cat > "$TMPFILE" << 'EPOCHS'
 (eval "(list er-echo-test-pass er-echo-test-count)")
 (epoch 108)
 (eval "(list er-fib-test-pass er-fib-test-count)")
+(epoch 109)
+(eval "(list er-ffi-test-pass er-ffi-test-count)")
+(epoch 110)
+(eval "(list er-vm-test-pass er-vm-test-count)")
+(epoch 111)
+(eval "(list er-sa-test-pass er-sa-test-count)")
 EPOCHS
 
 timeout 600 "$SX_SERVER" < "$TMPFILE" > "$OUTFILE" 2>&1

lib/erlang/scoreboard.json

@@ -1,16 +1,19 @@
 {
   "language": "erlang",
-  "total_pass": 530,
+  "total_pass": 771,
-  "total": 530,
+  "total": 771,
   "suites": [
     {"name":"tokenize","pass":62,"total":62,"status":"ok"},
     {"name":"parse","pass":52,"total":52,"status":"ok"},
-    {"name":"eval","pass":346,"total":346,"status":"ok"},
+    {"name":"eval","pass":408,"total":408,"status":"ok"},
-    {"name":"runtime","pass":39,"total":39,"status":"ok"},
+    {"name":"runtime","pass":93,"total":93,"status":"ok"},
     {"name":"ring","pass":4,"total":4,"status":"ok"},
     {"name":"ping-pong","pass":4,"total":4,"status":"ok"},
     {"name":"bank","pass":8,"total":8,"status":"ok"},
     {"name":"echo","pass":7,"total":7,"status":"ok"},
-    {"name":"fib","pass":8,"total":8,"status":"ok"}
+    {"name":"fib","pass":8,"total":8,"status":"ok"},
+    {"name":"ffi","pass":37,"total":37,"status":"ok"},
+    {"name":"vm","pass":78,"total":78,"status":"ok"},
+    {"name":"send_after","pass":10,"total":10,"status":"ok"}
   ]
 }

lib/erlang/scoreboard.md

@@ -1,18 +1,21 @@
 # Erlang-on-SX Scoreboard
 
-**Total: 530 / 530 tests passing**
+**Total: 771 / 771 tests passing**
 
 |  | Suite | Pass | Total |
 |---|---|---|---|
 | ✅ | tokenize | 62 | 62 |
 | ✅ | parse | 52 | 52 |
-| ✅ | eval | 346 | 346 |
+| ✅ | eval | 408 | 408 |
-| ✅ | runtime | 39 | 39 |
+| ✅ | runtime | 93 | 93 |
 | ✅ | ring | 4 | 4 |
 | ✅ | ping-pong | 4 | 4 |
 | ✅ | bank | 8 | 8 |
 | ✅ | echo | 7 | 7 |
 | ✅ | fib | 8 | 8 |
+| ✅ | ffi | 37 | 37 |
+| ✅ | vm | 78 | 78 |
+| ✅ | send_after | 10 | 10 |
 
 
 Generated by `lib/erlang/conformance.sh`.

lib/erlang/tests/eval.sx

@@ -228,9 +228,10 @@
 (er-eval-test "tuple_size 0" (ev "tuple_size({})") 0)
 
 ;; ── BIFs: atom / list conversions ───────────────────────────────
-(er-eval-test "atom_to_list" (ev "atom_to_list(hello)") "hello")
+(er-eval-test "atom_to_list -> charlist length" (ev "length(atom_to_list(hello))") 5)
+(er-eval-test "atom_to_list -> head $h" (ev "hd(atom_to_list(hello))") 104)
 (er-eval-test "list_to_atom roundtrip"
-  (nm (ev "list_to_atom(atom_to_list(foo))")) "foo")
+  (nm (ev "list_to_atom(atom_to_list(foo))")) "foo")  ;; round-trip via charlist
 (er-eval-test "list_to_atom fresh"
   (nm (ev "list_to_atom(\"bar\")")) "bar")
 
@@ -1060,11 +1061,13 @@
 (er-eval-test "list_to_tuple roundtrip"
   (ev "tuple_size(list_to_tuple([10, 20, 30]))") 3)
 
-(er-eval-test "integer_to_list" (ev "integer_to_list(42)") "42")
+(er-eval-test "integer_to_list -> charlist length" (ev "length(integer_to_list(42))") 2)
-(er-eval-test "integer_to_list neg" (ev "integer_to_list(-99)") "-99")
+(er-eval-test "integer_to_list 42 head $4" (ev "hd(integer_to_list(42))") 52)
+(er-eval-test "integer_to_list neg -> charlist length" (ev "length(integer_to_list(-99))") 3)
+(er-eval-test "integer_to_list -99 head $-" (ev "hd(integer_to_list(-99))") 45)
 (er-eval-test "list_to_integer" (ev "list_to_integer(\"123\")") 123)
 (er-eval-test "list_to_integer roundtrip"
-  (ev "list_to_integer(integer_to_list(7))") 7)
+  (ev "list_to_integer(integer_to_list(7))") 7)  ;; round-trip via charlist
 
 (er-eval-test "is_function fun"
   (nm (ev "F = fun (X) -> X end, is_function(F)")) "true")
@@ -1125,6 +1128,258 @@
 (er-eval-test "lists:duplicate val"
   (nm (ev "hd(lists:duplicate(3, marker))")) "marker")
 
+
+;; ── Phase 7: code:load_binary/3 ───────────────────────────────
+(er-modules-reset!)
+
+(er-eval-test "code:load_binary ok tag"
+  (nm (ev "element(1, code:load_binary(cl1, \"cl1.erl\", \"-module(cl1). foo() -> 1.\"))"))
+  "module")
+(er-eval-test "code:load_binary ok name"
+  (nm (ev "element(2, code:load_binary(cl1, \"cl1.erl\", \"-module(cl1). foo() -> 1.\"))"))
+  "cl1")
+(er-eval-test "code:load_binary then call"
+  (ev "cl1:foo()") 1)
+
+(er-eval-test "code:load_binary reload v2"
+  (ev "code:load_binary(cl1, \"cl1.erl\", \"-module(cl1). foo() -> 99.\"), cl1:foo()")
+  99)
+
+(er-eval-test "code:load_binary name mismatch tag"
+  (nm (ev "element(1, code:load_binary(cl2, \"x.erl\", \"-module(other). f() -> 0.\"))"))
+  "error")
+(er-eval-test "code:load_binary name mismatch reason"
+  (nm (ev "element(2, code:load_binary(cl2, \"x.erl\", \"-module(other). f() -> 0.\"))"))
+  "module_name_mismatch")
+
+(er-eval-test "code:load_binary badfile on garbage"
+  (nm (ev "element(2, code:load_binary(cl3, \"x.erl\", \"this is not erlang\"))"))
+  "badfile")
+
+(er-eval-test "code:load_binary non-atom mod is badarg"
+  (nm (ev "element(2, code:load_binary(\"cl1\", \"x.erl\", \"-module(cl1). f() -> 0.\"))"))
+  "badarg")
+
+
+;; ── Phase 7: code:purge/1 + code:soft_purge/1 ───────────────────
+(er-modules-reset!)
+
+;; purge unknown module → false
+(er-eval-test "code:purge unknown"
+  (nm (ev "code:purge(nope)")) "false")
+
+;; load, then purge without old version → false (nothing to purge)
+(er-eval-test "code:purge no old"
+  (nm (ev "code:load_binary(pg1, \"pg1\", \"-module(pg1). v() -> 1.\"), code:purge(pg1)"))
+  "false")
+
+;; load v1, load v2 (creates :old), purge with no live procs → true
+(er-eval-test "code:purge after reload"
+  (nm (ev "code:load_binary(pg2, \"pg2\", \"-module(pg2). v() -> 1.\"), code:load_binary(pg2, \"pg2\", \"-module(pg2). v() -> 2.\"), code:purge(pg2)"))
+  "true")
+
+;; idempotent: purging again returns false (already purged)
+(er-eval-test "code:purge twice"
+  (nm (ev "code:load_binary(pg3, \"pg3\", \"-module(pg3). v() -> 1.\"), code:load_binary(pg3, \"pg3\", \"-module(pg3). v() -> 2.\"), code:purge(pg3), code:purge(pg3)"))
+  "false")
+
+;; purge returns true whenever an :old slot exists, regardless of process tracking
+;; (proper "kill lingering" semantics requires spawn/3 which is still stubbed)
+(er-eval-test "code:purge with old slot present"
+  (nm (ev "code:load_binary(pg4, \"pg4\", \"-module(pg4). loop() -> receive stop -> ok end.\"),
+           Pid = spawn(fun () -> pg4:loop() end),
+           code:load_binary(pg4, \"pg4\", \"-module(pg4). loop() -> receive stop -> done end.\"),
+           code:purge(pg4)"))
+  "true")
+
+;; soft_purge unknown → true (nothing to purge)
+(er-eval-test "code:soft_purge unknown"
+  (nm (ev "code:soft_purge(nope)")) "true")
+
+;; soft_purge with no old version → true
+(er-eval-test "code:soft_purge no old"
+  (nm (ev "code:load_binary(sp1, \"sp1\", \"-module(sp1). v() -> 1.\"), code:soft_purge(sp1)"))
+  "true")
+
+;; soft_purge with old + no lingering procs → true (clears :old)
+(er-eval-test "code:soft_purge clean"
+  (nm (ev "code:load_binary(sp2, \"sp2\", \"-module(sp2). v() -> 1.\"), code:load_binary(sp2, \"sp2\", \"-module(sp2). v() -> 2.\"), code:soft_purge(sp2)"))
+  "true")
+
+;; non-atom Mod is badarg (raise)
+(er-eval-test "code:purge badarg"
+  (nm (ev "try code:purge(\"str\") catch error:badarg -> ok end")) "ok")
+(er-eval-test "code:soft_purge badarg"
+  (nm (ev "try code:soft_purge(123) catch error:badarg -> ok end")) "ok")
+
+
+;; ── Phase 7: code:which/1 + code:is_loaded/1 + code:all_loaded/0 ──
+(er-modules-reset!)
+
+(er-eval-test "code:which non_existing"
+  (nm (ev "code:which(nope)")) "non_existing")
+
+(er-eval-test "code:which after load"
+  (nm (ev "code:load_binary(wh1, \"wh1\", \"-module(wh1). v() -> 1.\"), code:which(wh1)"))
+  "loaded")
+
+(er-eval-test "code:is_loaded missing"
+  (nm (ev "code:is_loaded(nope)")) "false")
+
+(er-eval-test "code:is_loaded tag"
+  (nm (ev "code:load_binary(il1, \"il1\", \"-module(il1). v() -> 1.\"), element(1, code:is_loaded(il1))"))
+  "file")
+
+(er-eval-test "code:is_loaded value"
+  (nm (ev "code:load_binary(il2, \"il2\", \"-module(il2). v() -> 1.\"), element(2, code:is_loaded(il2))"))
+  "loaded")
+
+(er-modules-reset!)
+(er-eval-test "code:all_loaded empty"
+  (ev "length(code:all_loaded())") 0)
+
+(er-modules-reset!)
+(er-eval-test "code:all_loaded count"
+  (ev "code:load_binary(al1, \"al1\", \"-module(al1). v() -> 1.\"),
+       code:load_binary(al2, \"al2\", \"-module(al2). v() -> 1.\"),
+       length(code:all_loaded())")
+  2)
+
+(er-eval-test "code:all_loaded first entry tag"
+  (nm (ev "code:load_binary(al3, \"al3\", \"-module(al3). v() -> 1.\"),
+           element(2, hd(code:all_loaded()))"))
+  "loaded")
+
+(er-eval-test "code:which badarg"
+  (nm (ev "try code:which(\"str\") catch error:badarg -> ok end")) "ok")
+(er-eval-test "code:is_loaded badarg"
+  (nm (ev "try code:is_loaded(123) catch error:badarg -> ok end")) "ok")
+
+
+;; ── Phase 7: hot-reload call dispatch semantics ──────────────────
+;; Cross-module M:F() calls always hit the CURRENT version;
+;; local F() calls inside a module body resolve through the env
+;; the function closed over (i.e. the version it was loaded with).
+
+(er-modules-reset!)
+
+;; M:F always hits current
+(er-eval-test "cross-mod after reload v2"
+  (ev "code:load_binary(hr1, \"hr1\", \"-module(hr1). f() -> 1.\"),
+       code:load_binary(hr1, \"hr1\", \"-module(hr1). f() -> 2.\"),
+       hr1:f()")
+  2)
+
+;; Local call inside reloaded module body resolves via fresh mod-env
+;; (a() does a local b(); b() got upgraded too)
+(er-eval-test "local call inside reloaded module body"
+  (ev "code:load_binary(hr2, \"hr2\", \"-module(hr2). a() -> b(). b() -> 1.\"),
+       code:load_binary(hr2, \"hr2\", \"-module(hr2). a() -> b(). b() -> 99.\"),
+       hr2:a()")
+  99)
+
+;; Fun captured BEFORE reload, with local-call body, keeps v1 semantics
+(er-eval-test "captured fun keeps closed-over env (local call)"
+  (ev "code:load_binary(hr3, \"hr3\", \"-module(hr3). get_fn() -> fun () -> b() end. b() -> 1.\"),
+       Fn = hr3:get_fn(),
+       code:load_binary(hr3, \"hr3\", \"-module(hr3). get_fn() -> fun () -> b() end. b() -> 99.\"),
+       Fn()")
+  1)
+
+;; Fun captured BEFORE reload, with CROSS-mod body, sees v2's current
+(er-eval-test "captured fun follows cross-mod to current"
+  (ev "code:load_binary(hr4, \"hr4\", \"-module(hr4). get_xref() -> fun () -> hr4:b() end. b() -> 1.\"),
+       Fn = hr4:get_xref(),
+       code:load_binary(hr4, \"hr4\", \"-module(hr4). get_xref() -> fun () -> hr4:b() end. b() -> 99.\"),
+       Fn()")
+  99)
+
+;; Two captured funs from two different vintages
+(er-eval-test "two funs from two vintages stay independent"
+  (ev "code:load_binary(hr5, \"hr5\", \"-module(hr5). gf() -> fun () -> v() end. v() -> 10.\"),
+       F1 = hr5:gf(),
+       code:load_binary(hr5, \"hr5\", \"-module(hr5). gf() -> fun () -> v() end. v() -> 20.\"),
+       F2 = hr5:gf(),
+       F1() + F2()")
+  30)
+
+;; Version slot bumps correctly when a captured fun stays alive
+(er-eval-test "version bumps despite captured funs"
+  (ev "code:load_binary(hr6, \"hr6\", \"-module(hr6). gf() -> fun () -> v() end. v() -> 1.\"),
+       _Pinned = hr6:gf(),
+       code:load_binary(hr6, \"hr6\", \"-module(hr6). gf() -> fun () -> v() end. v() -> 2.\"),
+       code:load_binary(hr6, \"hr6\", \"-module(hr6). gf() -> fun () -> v() end. v() -> 3.\"),
+       hr6:v()")
+  3)
+
+
+
+;; ── Phase 7 capstone: full hot-reload ladder ───────────────────
+;; Load v1 → spawn from inside module → load v2 → cross-mod hits v2 →
+;; local call inside v1 process still resolves v1 → soft_purge refuses
+;; while v1 procs alive → purge kills them.
+;;
+;; All stages must run in a single erlang-eval-ast call: each call resets
+;; the scheduler (er-sched-init!) so cross-call Pid handles would point at
+;; reaped processes.
+(er-modules-reset!)
+
+(define er-rt-cap-prog "code:load_binary(cap, \"cap.erl\", \"-module(cap). start() -> spawn(fun () -> loop() end). loop() -> receive {ping, From} -> From ! {pong, v1}, loop(); stop -> done end. tag() -> v1.\"), Tag1 = cap:tag(), Pid1 = cap:start(), code:load_binary(cap, \"cap.erl\", \"-module(cap). start() -> spawn(fun () -> loop() end). loop() -> receive {ping, From} -> From ! {pong, v2}, loop(); stop -> done end. tag() -> v2.\"), Tag2 = cap:tag(), _Pid2 = cap:start(), Soft1 = code:soft_purge(cap), Hard = code:purge(cap), Soft2 = code:soft_purge(cap), {Tag1, Tag2, Soft1, Hard, Soft2}")
+
+(define er-rt-cap-result (ev er-rt-cap-prog))
+
+(er-eval-test "capstone v1 tag direct"
+  (get (nth (get er-rt-cap-result :elements) 0) :name) "v1")
+
+(er-eval-test "capstone v2 tag"
+  (get (nth (get er-rt-cap-result :elements) 1) :name) "v2")
+
+(er-eval-test "capstone soft_purge while v1 alive = false"
+  (get (nth (get er-rt-cap-result :elements) 2) :name) "false")
+
+(er-eval-test "capstone hard purge = true"
+  (get (nth (get er-rt-cap-result :elements) 3) :name) "true")
+
+(er-eval-test "capstone soft_purge clean after hard = true"
+  (get (nth (get er-rt-cap-result :elements) 4) :name) "true")
+
+
+
+;; ── $X char literals (Step 3b substrate fix 2026-06-04) ──────────
+(er-eval-test "char $A" (ev "$A") 65)
+(er-eval-test "char $a" (ev "$a") 97)
+(er-eval-test "char $0 is digit, not escape-NUL" (ev "$0") 48)
+(er-eval-test "char $\\n is newline (10)" (ev "$\\n") 10)
+(er-eval-test "char $\\t is tab (9)" (ev "$\\t") 9)
+(er-eval-test "char $\\r is CR (13)" (ev "$\\r") 13)
+(er-eval-test "char $\\s is space (32)" (ev "$\\s") 32)
+(er-eval-test "char $\\0 is NUL (0)" (ev "$\\0") 0)
+(er-eval-test "char $\\\\ is backslash (92)" (ev "$\\\\") 92)
+(er-eval-test "[$h,$i] head is 104" (ev "hd([$h, $i])") 104)
+(er-eval-test "list_to_binary char-list -> bytes"
+  (ev "byte_size(list_to_binary([$f, $e, $d]))") 3)
+(er-eval-test "list_to_binary char-list round-trip"
+  (nm (ev "list_to_binary([$h, $i]) =:= <<104, 105>>")) "true")
+
+
+;; ── atom_to_list / integer_to_list charlist semantics (Step 3b substrate fix #3) ──
+(er-eval-test "atom_to_list hd is char code"
+  (ev "hd(atom_to_list(hi))") 104)
+(er-eval-test "atom_to_list maps to bytes via list_to_binary"
+  (ev "byte_size(list_to_binary(atom_to_list(hello)))") 5)
+(er-eval-test "atom_to_list -> list_to_binary -> bytes content"
+  (nm (ev "list_to_binary(atom_to_list(ok)) =:= <<111, 107>>")) "true")
+(er-eval-test "integer_to_list 12345 -> 5 chars"
+  (ev "length(integer_to_list(12345))") 5)
+(er-eval-test "integer_to_list -> bytes -> back"
+  (ev "list_to_integer(integer_to_list(99999))") 99999)
+(er-eval-test "list_to_atom from charlist"
+  (nm (ev "list_to_atom([$f, $o, $o])")) "foo")
+(er-eval-test "list_to_atom from SX-string back-compat"
+  (nm (ev "list_to_atom(\"bar\")")) "bar")
+(er-eval-test "list_to_integer from charlist"
+  (ev "list_to_integer([$1, $0, $0])") 100)
+
 (define
   er-eval-test-summary
   (str "eval " er-eval-test-pass "/" er-eval-test-count))

lib/erlang/tests/ffi.sx

@@ -0,0 +1,223 @@
+;; Phase 8 FFI BIF tests — one round-trip per BIF.
+;; Each BIF lives in lib/erlang/runtime.sx (registered with
+;; er-bif-registry) and wraps an SX-host primitive.
+
+(define er-ffi-test-count 0)
+(define er-ffi-test-pass 0)
+(define er-ffi-test-fails (list))
+
+(define
+  er-ffi-test
+  (fn
+    (name actual expected)
+    (set! er-ffi-test-count (+ er-ffi-test-count 1))
+    (if
+      (= actual expected)
+      (set! er-ffi-test-pass (+ er-ffi-test-pass 1))
+      (append! er-ffi-test-fails {:name name :expected expected :actual actual}))))
+
+(define ffi-ev erlang-eval-ast)
+(define ffi-nm (fn (v) (get v :name)))
+
+;; ── file:read_file/1 + file:write_file/2 ────────────────────────
+(er-ffi-test
+  "file:write_file ok"
+  (ffi-nm (ffi-ev "file:write_file(\"/tmp/er-ffi-1.txt\", \"hello\")"))
+  "ok")
+
+(er-ffi-test
+  "file:read_file ok tag"
+  (ffi-nm (ffi-ev "element(1, file:read_file(\"/tmp/er-ffi-1.txt\"))"))
+  "ok")
+
+(er-ffi-test
+  "file:read_file payload is binary"
+  (ffi-nm
+    (ffi-ev
+      "case file:read_file(\"/tmp/er-ffi-1.txt\") of {ok, B} -> is_binary(B) end"))
+  "true")
+
+(er-ffi-test
+  "file:read_file content byte_size"
+  (ffi-ev
+    "case file:read_file(\"/tmp/er-ffi-1.txt\") of {ok, B} -> byte_size(B) end")
+  5)
+
+(er-ffi-test
+  "file:read_file missing enoent"
+  (ffi-nm (ffi-ev "element(2, file:read_file(\"/tmp/er-ffi-no-such-xyz\"))"))
+  "enoent")
+
+(er-ffi-test
+  "file:write_file bad path enoent"
+  (ffi-nm
+    (ffi-ev "element(2, file:write_file(\"/tmp/er-ffi-no-dir-xyz/x\", \"y\"))"))
+  "enoent")
+
+(er-ffi-test
+  "file:write_file binary payload"
+  (ffi-ev
+    "file:write_file(\"/tmp/er-ffi-2.bin\", <<1, 2, 3, 4, 5>>), case file:read_file(\"/tmp/er-ffi-2.bin\") of {ok, B} -> byte_size(B) end")
+  5)
+
+;; ── file:delete/1 ────────────────────────────────────────────────
+(er-ffi-test
+  "file:delete ok"
+  (ffi-nm
+    (ffi-ev
+      "file:write_file(\"/tmp/er-ffi-del.txt\", \"x\"), file:delete(\"/tmp/er-ffi-del.txt\")"))
+  "ok")
+
+(er-ffi-test
+  "file:read_file after delete enoent"
+  (ffi-nm
+    (ffi-ev
+      "file:write_file(\"/tmp/er-ffi-del2.txt\", \"x\"), file:delete(\"/tmp/er-ffi-del2.txt\"), element(2, file:read_file(\"/tmp/er-ffi-del2.txt\"))"))
+  "enoent")
+
+(er-ffi-test
+  "crypto:hash sha256 -> 32-byte binary"
+  (ffi-ev "byte_size(crypto:hash(sha256, <<97,98,99>>))")
+  32)
+
+(er-ffi-test
+  "crypto:hash sha512 -> 64-byte binary"
+  (ffi-ev "byte_size(crypto:hash(sha512, <<97,98,99>>))")
+  64)
+
+(er-ffi-test
+  "crypto:hash sha3_256 is_binary"
+  (ffi-nm (ffi-ev "is_binary(crypto:hash(sha3_256, <<120>>))"))
+  "true")
+
+(er-ffi-test
+  "crypto:hash deterministic"
+  (ffi-nm (ffi-ev "crypto:hash(sha256, <<97>>) =:= crypto:hash(sha256, <<97>>)"))
+  "true")
+
+(er-ffi-test
+  "crypto:hash distinct inputs distinct digests"
+  (ffi-nm (ffi-ev "crypto:hash(sha256, <<97>>) =/= crypto:hash(sha256, <<98>>)"))
+  "true")
+
+(er-ffi-test
+  "crypto:hash bad type -> error:badarg"
+  (ffi-nm (ffi-ev "try crypto:hash(md5, <<120>>) catch error:badarg -> ok end"))
+  "ok")
+
+(er-ffi-test
+  "cid:from_bytes is_binary"
+  (ffi-nm (ffi-ev "is_binary(cid:from_bytes(<<97,98,99>>))"))
+  "true")
+
+(er-ffi-test
+  "cid:from_bytes deterministic"
+  (ffi-nm (ffi-ev "cid:from_bytes(<<97,98,99>>) =:= cid:from_bytes(<<97,98,99>>)"))
+  "true")
+
+(er-ffi-test
+  "cid:from_bytes distinct inputs distinct CIDs"
+  (ffi-nm (ffi-ev "cid:from_bytes(<<97,98,99>>) =/= cid:from_bytes(<<97,98,100>>)"))
+  "true")
+
+(er-ffi-test
+  "cid:from_bytes non-binary -> error:badarg"
+  (ffi-nm (ffi-ev "try cid:from_bytes(42) catch error:badarg -> ok end"))
+  "ok")
+
+(er-ffi-test
+  "cid:to_string is_binary"
+  (ffi-nm (ffi-ev "is_binary(cid:to_string({ok, 42}))"))
+  "true")
+
+(er-ffi-test
+  "cid:to_string deterministic"
+  (ffi-nm (ffi-ev "cid:to_string(foo) =:= cid:to_string(foo)"))
+  "true")
+
+(er-ffi-test
+  "cid:to_string distinct terms distinct CIDs"
+  (ffi-nm (ffi-ev "cid:to_string(foo) =/= cid:to_string(bar)"))
+  "true")
+
+(er-ffi-test
+  "file:list_dir ok tag"
+  (ffi-nm (ffi-ev "element(1, file:list_dir(\"lib/erlang\"))"))
+  "ok")
+
+(er-ffi-test
+  "file:list_dir non-empty"
+  (ffi-nm (ffi-ev "case file:list_dir(\"lib/erlang\") of {ok, L} -> length(L) > 3 end"))
+  "true")
+
+(er-ffi-test
+  "file:list_dir entries are binaries"
+  (ffi-nm (ffi-ev "case file:list_dir(\"lib/erlang\") of {ok, L} -> is_binary(hd(L)) end"))
+  "true")
+
+(er-ffi-test
+  "file:list_dir missing enoent"
+  (ffi-nm (ffi-ev "element(2, file:list_dir(\"/no/such/dir/xyz\"))"))
+  "enoent")
+
+(er-ffi-test
+  "binary_to_list <<1,2,3>> length"
+  (ffi-ev "length(binary_to_list(<<1,2,3,4,5>>))")
+  5)
+
+(er-ffi-test
+  "binary_to_list hd byte"
+  (ffi-ev "hd(binary_to_list(<<7,8,9>>))")
+  7)
+
+(er-ffi-test
+  "binary_to_list empty -> []"
+  (ffi-nm (ffi-ev "case binary_to_list(<<>>) of [] -> empty end"))
+  "empty")
+
+(er-ffi-test
+  "list_to_binary flat list bytes"
+  (ffi-ev "byte_size(list_to_binary([1,2,3]))")
+  3)
+
+(er-ffi-test
+  "list_to_binary nested iolist"
+  (ffi-ev "byte_size(list_to_binary([1, <<2,3>>, [4, [5]]]))")
+  5)
+
+(er-ffi-test
+  "list_to_binary round-trip via binary_to_list"
+  (ffi-nm (ffi-ev "list_to_binary(binary_to_list(<<10,20,30>>)) =:= <<10,20,30>>"))
+  "true")
+
+(er-ffi-test
+  "binary_to_list non-binary -> error:badarg"
+  (ffi-nm (ffi-ev "try binary_to_list(42) catch error:badarg -> ok end"))
+  "ok")
+
+(er-ffi-test
+  "list_to_binary out-of-range byte -> error:badarg"
+  (ffi-nm (ffi-ev "try list_to_binary([300]) catch error:badarg -> ok end"))
+  "ok")
+
+(er-ffi-test
+  "list_to_binary non-iolist -> error:badarg"
+  (ffi-nm (ffi-ev "try list_to_binary(42) catch error:badarg -> ok end"))
+  "ok")
+
+;; ── Still deferred (no host primitive): httpc (HTTP client, v2),
+;; sqlite-* (v2 indexes). Assert NOT registered so a future iteration
+;; that wires them without updating this suite fails fast.
+(er-ffi-test
+  "httpc:request unregistered"
+  (er-lookup-bif "httpc" "request" 4)
+  nil)
+
+(er-ffi-test
+  "sqlite:exec unregistered"
+  (er-lookup-bif "sqlite" "exec" 2)
+  nil)
+
+(define
+  er-ffi-test-summary
+  (str "ffi " er-ffi-test-pass "/" er-ffi-test-count))

lib/erlang/tests/runtime.sx

@@ -134,6 +134,144 @@
   (er-sched-current-pid)
   nil)
 
+
+
+;; ── Phase 7: module-version slots ───────────────────────────────
+(er-modules-reset!)
+
+(define er-rt-slot1 (er-mk-module-slot (er-env-new) nil 1))
+(er-rt-test "slot tag"     (get er-rt-slot1 :tag)              "module")
+(er-rt-test "slot version" (er-module-version er-rt-slot1)     1)
+(er-rt-test "slot old nil" (er-module-old-env er-rt-slot1)     nil)
+(er-rt-test "slot current not nil" (= (er-module-current-env er-rt-slot1) nil) false)
+
+(erlang-load-module "-module(hr1). a() -> 1.")
+(define er-rt-reg (er-modules-get))
+(er-rt-test "registry has hr1"     (dict-has? er-rt-reg "hr1")                       true)
+(er-rt-test "v1 on first load"     (er-module-version (get er-rt-reg "hr1"))         1)
+(er-rt-test "v1 old is nil"        (er-module-old-env (get er-rt-reg "hr1"))         nil)
+(er-rt-test "v1 current not nil"   (= (er-module-current-env (get er-rt-reg "hr1")) nil) false)
+
+(define er-rt-env-v1 (er-module-current-env (get er-rt-reg "hr1")))
+(erlang-load-module "-module(hr1). a() -> 2.")
+(er-rt-test "v2 on second load"    (er-module-version (get er-rt-reg "hr1"))         2)
+(er-rt-test "v2 old is v1 env"     (er-module-old-env (get er-rt-reg "hr1"))         er-rt-env-v1)
+(er-rt-test "v2 current is new"    (= (er-module-current-env (get er-rt-reg "hr1")) er-rt-env-v1) false)
+
+(erlang-load-module "-module(hr1). a() -> 3.")
+(er-rt-test "v3 on third load"     (er-module-version (get er-rt-reg "hr1"))         3)
+
+(er-modules-reset!)
+(er-rt-test "registry-reset clears" (dict-has? (er-modules-get) "hr1")              false)
+
+
+
+
+;; ── Phase 8: FFI BIF registry ──────────────────────────────────
+(er-bif-registry-reset!)
+
+(er-rt-test "empty registry" (len (er-list-bifs)) 0)
+(er-rt-test "lookup miss" (er-lookup-bif "crypto" "hash" 2) nil)
+
+(er-register-bif! "fake" "echo" 1 (fn (vs) (nth vs 0)))
+(er-rt-test "register grows registry" (len (er-list-bifs)) 1)
+
+(define er-rt-bif-hit (er-lookup-bif "fake" "echo" 1))
+(er-rt-test "lookup hit module" (get er-rt-bif-hit :module) "fake")
+(er-rt-test "lookup hit name"   (get er-rt-bif-hit :name)   "echo")
+(er-rt-test "lookup hit arity"  (get er-rt-bif-hit :arity)  1)
+(er-rt-test "lookup hit pure?"  (get er-rt-bif-hit :pure?)  false)
+
+(er-rt-test "fn invocable" ((get er-rt-bif-hit :fn) (list 42)) 42)
+
+;; Re-register replaces (same key)
+(er-register-bif! "fake" "echo" 1 (fn (vs) "replaced"))
+(er-rt-test "re-register same key, count unchanged" (len (er-list-bifs)) 1)
+(er-rt-test "re-register replaces fn"
+  ((get (er-lookup-bif "fake" "echo" 1) :fn) (list 99)) "replaced")
+
+;; Pure variant
+(er-register-pure-bif! "fake" "pure" 2 (fn (vs) (+ (nth vs 0) (nth vs 1))))
+(er-rt-test "pure registered separately, count 2" (len (er-list-bifs)) 2)
+(er-rt-test "pure flag true"
+  (get (er-lookup-bif "fake" "pure" 2) :pure?) true)
+(er-rt-test "pure fn invocable"
+  ((get (er-lookup-bif "fake" "pure" 2) :fn) (list 7 8)) 15)
+
+;; Arity disambiguation: same module+name, different arity = distinct entries
+(er-register-bif! "fake" "echo" 2 (fn (vs) (list (nth vs 0) (nth vs 1))))
+(er-rt-test "arity disambiguation count" (len (er-list-bifs)) 3)
+(er-rt-test "arity-1 lookup still works"
+  ((get (er-lookup-bif "fake" "echo" 1) :fn) (list 11)) "replaced")
+(er-rt-test "arity-2 lookup independent"
+  (len ((get (er-lookup-bif "fake" "echo" 2) :fn) (list 1 2))) 2)
+
+;; Reset clears the registry
+(er-bif-registry-reset!)
+(er-rt-test "reset clears" (len (er-list-bifs)) 0)
+(er-rt-test "reset lookup nil" (er-lookup-bif "fake" "echo" 1) nil)
+
+
+
+;; ── Phase 8: term marshalling (er-to-sx / er-of-sx) ─────────────
+
+;; er-to-sx: Erlang → SX
+(er-rt-test "to-sx atom"      (er-to-sx (er-mk-atom "foo"))         (make-symbol "foo"))
+(er-rt-test "to-sx atom is symbol" (type-of (er-to-sx (er-mk-atom "x"))) "symbol")
+(er-rt-test "to-sx nil"       (er-to-sx (er-mk-nil))                (list))
+(er-rt-test "to-sx integer passthrough" (er-to-sx 42)               42)
+(er-rt-test "to-sx float passthrough"   (er-to-sx 3.14)             3.14)
+(er-rt-test "to-sx boolean passthrough" (er-to-sx true)             true)
+(er-rt-test "to-sx binary → string"
+  (er-to-sx (er-mk-binary (list 104 105 33))) "hi!")
+(er-rt-test "to-sx cons → list"
+  (er-to-sx (er-mk-cons 1 (er-mk-cons 2 (er-mk-cons 3 (er-mk-nil))))) (list 1 2 3))
+(er-rt-test "to-sx tuple → list"
+  (er-to-sx (er-mk-tuple (list 1 2 3))) (list 1 2 3))
+(er-rt-test "to-sx nested cons"
+  (er-to-sx (er-mk-cons (er-mk-atom "a") (er-mk-cons 7 (er-mk-nil))))
+  (list (make-symbol "a") 7))
+
+;; er-of-sx: SX → Erlang
+(er-rt-test "of-sx symbol"
+  (get (er-of-sx (make-symbol "ok")) :name) "ok")
+(er-rt-test "of-sx symbol is atom"
+  (er-atom? (er-of-sx (make-symbol "x"))) true)
+(er-rt-test "of-sx string is binary"
+  (er-binary? (er-of-sx "hi")) true)
+(er-rt-test "of-sx string bytes"
+  (get (er-of-sx "hi") :bytes) (list 104 105))
+(er-rt-test "of-sx integer passthrough"
+  (er-of-sx 42) 42)
+(er-rt-test "of-sx empty list → nil"
+  (er-nil? (er-of-sx (list))) true)
+(er-rt-test "of-sx list → cons chain length"
+  (er-list-length (er-of-sx (list 1 2 3 4))) 4)
+(er-rt-test "of-sx list head/tail"
+  (get (er-of-sx (list 10 20)) :head) 10)
+
+;; Round-trips
+(er-rt-test "rtrip integer" (er-to-sx (er-of-sx 99)) 99)
+(er-rt-test "rtrip atom"
+  (get (er-of-sx (er-to-sx (er-mk-atom "abc"))) :name) "abc")
+(er-rt-test "rtrip binary bytes"
+  (get (er-of-sx (er-to-sx (er-mk-binary (list 1 2 3)))) :bytes) (list 1 2 3))
+(er-rt-test "rtrip cons-of-ints length"
+  (er-list-length (er-of-sx (er-to-sx
+    (er-mk-cons 1 (er-mk-cons 2 (er-mk-cons 3 (er-mk-nil))))))) 3)
+
+;; Tuples don't round-trip exactly (er-to-sx flattens tuples to lists);
+;; documented one-way conversion.
+(er-rt-test "to-sx of tuple loses tag"
+  (er-cons? (er-of-sx (er-to-sx (er-mk-tuple (list 1 2 3))))) true)
+
+
+;; Re-populate built-in BIFs so subsequent test files (ring, ping-pong, etc.)
+;; can call length/spawn/etc. The migration onto the registry means a reset
+;; here would otherwise break the rest of the conformance suite.
+(er-register-builtin-bifs!)
+
+
 (define
   er-rt-test-summary
   (str "runtime " er-rt-test-pass "/" er-rt-test-count))

lib/erlang/tests/send_after.sx

@@ -0,0 +1,163 @@
+;; erlang:send_after / cancel_timer — timer primitives.
+;;
+;; A process schedules a message to itself (or another pid / registered
+;; name) after N logical milliseconds. `cancel_timer` removes a pending
+;; timer and reports the time left. These are the same primitives the
+;; gen_server library uses to implement `{noreply, State, Timeout}`.
+;;
+;; The scheduler runs a synchronous logical clock (see runtime.sx
+;; `er-sched-advance-time!`): time advances only when the runnable
+;; queue drains, jumping to the earliest pending deadline. That makes
+;; delivery deterministic and time-travel-safe — no wall clock.
+
+(define er-sa-test-count 0)
+(define er-sa-test-pass 0)
+(define er-sa-test-fails (list))
+
+(define
+  er-sa-test
+  (fn
+    (name actual expected)
+    (set! er-sa-test-count (+ er-sa-test-count 1))
+    (if
+      (= actual expected)
+      (set! er-sa-test-pass (+ er-sa-test-pass 1))
+      (append!
+        er-sa-test-fails
+        {:actual actual :expected expected :name name}))))
+
+(define er-sa-pred
+  (fn (name actual) (er-sa-test name (if actual true false) true)))
+
+(define sa-ev erlang-eval-ast)
+
+;; ── T1 — schedule a self-message, receive it after the deadline ──
+;; send_after returns a reference handle.
+(er-sa-pred
+  "T1 send_after returns a ref"
+  (er-ref?
+    (sa-ev "erlang:send_after(50, self(), hello)")))
+
+;; The scheduled message lands and a plain receive picks it up.
+(er-sa-test
+  "T1 delivered message received"
+  (get
+    (sa-ev
+      "erlang:send_after(50, self(), hello),
+       receive M -> M end")
+    :name)
+  "hello")
+
+;; Logical time advances exactly to the timer deadline (50ms) by the
+;; time the message is received — round-trip latency well under 100ms.
+(er-sa-test
+  "T1 clock at deadline on receipt"
+  (sa-ev
+    "erlang:send_after(50, self(), hello),
+     receive hello -> erlang:monotonic_time() end")
+  50)
+
+;; ── T2 — cancel_timer returns remaining ms; message never arrives ──
+;; Cancel immediately after scheduling: clock has not advanced, so the
+;; full duration (~1000ms) is reported as remaining.
+(er-sa-test
+  "T2 cancel returns remaining ms"
+  (sa-ev
+    "Ref = erlang:send_after(1000, self(), late),
+     erlang:cancel_timer(Ref)")
+  1000)
+
+;; The cancelled timer never delivers — the receive falls through to
+;; its `after` clause and returns `none`.
+(er-sa-test
+  "T2 cancelled message never arrives"
+  (get
+    (sa-ev
+      "Ref = erlang:send_after(1000, self(), late),
+       erlang:cancel_timer(Ref),
+       receive late -> got after 50 -> none end")
+    :name)
+  "none")
+
+;; ── T3 — multiple timers fire in deadline order, not schedule order ──
+;; `b` is scheduled first (deadline 80) but `a` second (deadline 20).
+;; Two plain receives drain the mailbox in arrival order — and arrival
+;; is governed by deadline, so the first message out is `a`.
+(er-sa-test
+  "T3 timers fire in deadline order"
+  (er-format-value
+    (sa-ev
+      "erlang:send_after(80, self(), b),
+       erlang:send_after(20, self(), a),
+       X = receive M1 -> M1 end,
+       Y = receive M2 -> M2 end,
+       {X, Y}"))
+  "{a,b}")
+
+;; A selective receive on `a` matches the earlier-deadline timer even
+;; though `b` was scheduled first.
+(er-sa-test
+  "T3 selective receive picks earliest deadline"
+  (get
+    (sa-ev
+      "erlang:send_after(80, self(), b),
+       erlang:send_after(20, self(), a),
+       receive a -> first end")
+    :name)
+  "first")
+
+;; ── T4 — cancel_timer on an already-fired timer returns false ──────
+;; Once `x` has been received the timer has fired; cancelling its ref
+;; now yields the atom `false`.
+(er-sa-test
+  "T4 cancel of fired timer is false"
+  (get
+    (sa-ev
+      "Ref = erlang:send_after(20, self(), x),
+       receive x -> ok end,
+       erlang:cancel_timer(Ref)")
+    :name)
+  "false")
+
+;; ── T5 — send_after to a registered atom name ──────────────────────
+;; A second process registers itself as `srv`; the timer addresses it
+;; by name, and the delayed message lands in that process's mailbox.
+;; The server forwards what it got back to the parent for inspection.
+(er-sa-test
+  "T5 timer delivers to registered name"
+  (get
+    (sa-ev
+      "Me = self(),
+       Pid = spawn(fun () -> receive M -> Me ! {got, M} end end),
+       register(srv, Pid),
+       erlang:send_after(20, srv, ping),
+       receive {got, X} -> X end")
+    :name)
+  "ping")
+
+;; ── T6 — gen_server {noreply, State, Timeout} hookup ───────────────
+;; A gen_server that, on the `arm` cast, returns {noreply, S, 100}.
+;; The library schedules {timeout} to itself via send_after; when no
+;; other message arrives first, handle_info({timeout}, S) fires. The
+;; handler signals the parent so we can confirm the timeout landed.
+(do
+  (er-load-gen-server!)
+  (erlang-load-module
+    "-module(sa_tmo).
+     init(Me) -> {ok, Me}.
+     handle_call(_R, _F, S) -> {reply, ok, S}.
+     handle_cast(arm, Me) -> {noreply, Me, 100}.
+     handle_info({timeout}, Me) -> Me ! fired, {noreply, Me};
+     handle_info(_M, S) -> {noreply, S}.")
+  nil)
+
+(er-sa-test
+  "T6 gen_server timeout fires handle_info"
+  (get
+    (sa-ev
+      "Me = self(),
+       P = gen_server:start_link(sa_tmo, Me),
+       gen_server:cast(P, arm),
+       receive fired -> ok after 5000 -> timeout end")
+    :name)
+  "ok")

lib/erlang/tests/vm.sx

@@ -0,0 +1,403 @@
+;; Phase 9 — stub VM opcode dispatcher tests.
+;; Verifies the dispatcher shape (mirrors plans/sx-vm-opcode-extension.md
+;; for when 9a integrates) and the three pattern-match opcodes (9b)
+;; route to the correct er-match-* impl.
+
+(define er-vm-test-count 0)
+(define er-vm-test-pass 0)
+(define er-vm-test-fails (list))
+
+(define
+  er-vm-test
+  (fn
+    (name actual expected)
+    (set! er-vm-test-count (+ er-vm-test-count 1))
+    (if
+      (= actual expected)
+      (set! er-vm-test-pass (+ er-vm-test-pass 1))
+      (append! er-vm-test-fails {:name name :expected expected :actual actual}))))
+
+;; ── dispatcher core ─────────────────────────────────────────────
+(er-vm-test
+  "tuple opcode registered"
+  (= (er-vm-lookup-opcode-by-id 128) nil)
+  false)
+
+(er-vm-test
+  "tuple opcode name"
+  (get (er-vm-lookup-opcode-by-id 128) :name)
+  "OP_PATTERN_TUPLE")
+
+(er-vm-test
+  "list opcode by name"
+  (get (er-vm-lookup-opcode-by-name "OP_PATTERN_LIST") :id)
+  129)
+
+(er-vm-test
+  "binary opcode by name"
+  (get (er-vm-lookup-opcode-by-name "OP_PATTERN_BINARY") :id)
+  130)
+
+(er-vm-test "lookup miss by id" (er-vm-lookup-opcode-by-id 999) nil)
+
+(er-vm-test "lookup miss by name" (er-vm-lookup-opcode-by-name "OP_NOPE") nil)
+
+(er-vm-test
+  "opcode list has 3+"
+  (>= (len (er-vm-list-opcodes)) 3)
+  true)
+
+;; ── OP_PATTERN_TUPLE ────────────────────────────────────────────
+;; Pattern: {ok, X} matches value {ok, 42} → X bound to 42
+(define er-vm-t1-env (er-env-new))
+(define er-vm-t1-pat {:type "tuple" :elements (list {:type "atom" :value "ok"} {:name "X" :type "var"})})
+(define er-vm-t1-val (er-mk-tuple (list (er-mk-atom "ok") 42)))
+(er-vm-test
+  "OP_PATTERN_TUPLE match"
+  (er-vm-dispatch 128 (list er-vm-t1-pat er-vm-t1-val er-vm-t1-env))
+  true)
+(er-vm-test "OP_PATTERN_TUPLE binds var" (get er-vm-t1-env "X") 42)
+
+;; Same pattern against {error, ...} → false
+(define er-vm-t2-env (er-env-new))
+(define er-vm-t2-val (er-mk-tuple (list (er-mk-atom "error") 7)))
+(er-vm-test
+  "OP_PATTERN_TUPLE no-match"
+  (er-vm-dispatch 128 (list er-vm-t1-pat er-vm-t2-val er-vm-t2-env))
+  false)
+
+;; Wrong arity tuple — pattern has 2 elements, value has 3
+(define er-vm-t3-env (er-env-new))
+(define
+  er-vm-t3-val
+  (er-mk-tuple (list (er-mk-atom "ok") 1 2)))
+(er-vm-test
+  "OP_PATTERN_TUPLE arity mismatch"
+  (er-vm-dispatch 128 (list er-vm-t1-pat er-vm-t3-val er-vm-t3-env))
+  false)
+
+;; ── OP_PATTERN_LIST (cons) ──────────────────────────────────────
+;; Pattern: [H | T] matches [1, 2, 3] → H=1, T=[2,3]
+(define er-vm-l1-env (er-env-new))
+(define er-vm-l1-pat {:type "cons" :tail {:name "T" :type "var"} :head {:name "H" :type "var"}})
+(define
+  er-vm-l1-val
+  (er-mk-cons
+    1
+    (er-mk-cons 2 (er-mk-cons 3 (er-mk-nil)))))
+(er-vm-test
+  "OP_PATTERN_LIST match"
+  (er-vm-dispatch 129 (list er-vm-l1-pat er-vm-l1-val er-vm-l1-env))
+  true)
+(er-vm-test "OP_PATTERN_LIST binds head" (get er-vm-l1-env "H") 1)
+(er-vm-test
+  "OP_PATTERN_LIST tail is cons"
+  (er-cons? (get er-vm-l1-env "T"))
+  true)
+
+;; [H|T] against empty list → false
+(define er-vm-l2-env (er-env-new))
+(er-vm-test
+  "OP_PATTERN_LIST no-match on nil"
+  (er-vm-dispatch 129 (list er-vm-l1-pat (er-mk-nil) er-vm-l2-env))
+  false)
+
+;; ── OP_PATTERN_BINARY ───────────────────────────────────────────
+;; Pattern <<A:8>> against <<42>> → A bound to 42
+(define er-vm-b1-env (er-env-new))
+(define er-vm-b1-pat {:type "binary" :segments (list {:value {:name "A" :type "var"} :size {:type "integer" :value "8"} :spec "integer"})})
+(define er-vm-b1-val (er-mk-binary (list 42)))
+(er-vm-test
+  "OP_PATTERN_BINARY match"
+  (er-vm-dispatch 130 (list er-vm-b1-pat er-vm-b1-val er-vm-b1-env))
+  true)
+(er-vm-test
+  "OP_PATTERN_BINARY binds segment"
+  (get er-vm-b1-env "A")
+  42)
+
+;; Same pattern against wrong-size binary (2 bytes) → false
+(define er-vm-b2-env (er-env-new))
+(define er-vm-b2-val (er-mk-binary (list 42 99)))
+(er-vm-test
+  "OP_PATTERN_BINARY size mismatch"
+  (er-vm-dispatch 130 (list er-vm-b1-pat er-vm-b2-val er-vm-b2-env))
+  false)
+
+;; ── dispatch error path ────────────────────────────────────────
+(define er-vm-err-caught (list nil))
+(guard
+  (c (:else (set-nth! er-vm-err-caught 0 (str c))))
+  (er-vm-dispatch 999 (list)))
+(er-vm-test
+  "unknown opcode raises"
+  (string-contains? (str (nth er-vm-err-caught 0)) "unknown opcode")
+  true)
+
+
+;; ── Phase 9c — OP_PERFORM / OP_HANDLE ───────────────────────────
+(er-vm-test "perform opcode by id"
+  (get (er-vm-lookup-opcode-by-id 131) :name) "OP_PERFORM")
+(er-vm-test "handle opcode by id"
+  (get (er-vm-lookup-opcode-by-id 132) :name) "OP_HANDLE")
+
+(define er-vm-pf-caught (list nil))
+(guard (c (:else (set-nth! er-vm-pf-caught 0 c)))
+  (er-vm-dispatch 131 (list "yield" (list 42))))
+(er-vm-test "perform raises tagged"
+  (get (nth er-vm-pf-caught 0) :tag) "vm-effect")
+(er-vm-test "perform effect name"
+  (get (nth er-vm-pf-caught 0) :effect) "yield")
+(er-vm-test "perform args carried"
+  (nth (get (nth er-vm-pf-caught 0) :args) 0) 42)
+
+(er-vm-test "handle catches matching effect"
+  (er-vm-dispatch 132
+    (list
+      (fn () (er-vm-dispatch 131 (list "yield" (list 7))))
+      "yield"
+      (fn (args) (+ (nth args 0) 100))))
+  107)
+
+(er-vm-test "handle no-effect returns thunk result"
+  (er-vm-dispatch 132
+    (list
+      (fn () 99)
+      "yield"
+      (fn (args) "handler ran")))
+  99)
+
+(define er-vm-rt-caught (list nil))
+(guard (c (:else (set-nth! er-vm-rt-caught 0 c)))
+  (er-vm-dispatch 132
+    (list
+      (fn () (er-vm-dispatch 131 (list "other" (list))))
+      "yield"
+      (fn (args) "wrong"))))
+(er-vm-test "handle rethrows non-matching"
+  (get (nth er-vm-rt-caught 0) :effect) "other")
+
+(er-vm-test "nested handles separate effect names"
+  (er-vm-dispatch 132
+    (list
+      (fn ()
+        (er-vm-dispatch 132
+          (list
+            (fn () (er-vm-dispatch 131 (list "b" (list 5))))
+            "a"
+            (fn (args) "inner-handled"))))
+      "b"
+      (fn (args) (+ (nth args 0) 1000))))
+  1005)
+
+
+;; ── Phase 9d — OP_RECEIVE_SCAN ──────────────────────────────────
+(er-vm-test "receive-scan opcode by id"
+  (get (er-vm-lookup-opcode-by-id 133) :name) "OP_RECEIVE_SCAN")
+
+;; Pattern: receive {ok, X} -> X end  against mailbox [{error, 1}, {ok, 42}, foo]
+(define er-vm-r1-env (er-env-new))
+(define er-vm-r1-clauses
+  (list
+    {:pattern {:type "tuple"
+               :elements (list
+                 {:type "atom" :value "ok"}
+                 {:type "var" :name "X"})}
+     :guards (list)
+     :body (list {:type "var" :name "X"})}))
+(define er-vm-r1-mbox
+  (list
+    (er-mk-tuple (list (er-mk-atom "error") 1))
+    (er-mk-tuple (list (er-mk-atom "ok") 42))
+    (er-mk-atom "foo")))
+
+(define er-vm-r1-result
+  (er-vm-dispatch 133 (list er-vm-r1-clauses er-vm-r1-mbox er-vm-r1-env)))
+(er-vm-test "scan finds match"
+  (get er-vm-r1-result :matched) true)
+(er-vm-test "scan reports correct index"
+  (get er-vm-r1-result :index) 1)
+(er-vm-test "scan binds var"
+  (get er-vm-r1-env "X") 42)
+(er-vm-test "scan leaves body unevaluated"
+  (= (get er-vm-r1-result :body) nil) false)
+
+;; No match case
+(define er-vm-r2-env (er-env-new))
+(define er-vm-r2-mbox (list (er-mk-atom "nope") 99))
+(define er-vm-r2-result
+  (er-vm-dispatch 133 (list er-vm-r1-clauses er-vm-r2-mbox er-vm-r2-env)))
+(er-vm-test "scan no-match"
+  (get er-vm-r2-result :matched) false)
+(er-vm-test "scan no-match leaves env clean"
+  (dict-has? er-vm-r2-env "X") false)
+
+;; Empty mailbox
+(define er-vm-r3-result
+  (er-vm-dispatch 133 (list er-vm-r1-clauses (list) (er-env-new))))
+(er-vm-test "scan empty mailbox"
+  (get er-vm-r3-result :matched) false)
+
+;; First-match wins (arrival order)
+(define er-vm-r4-env (er-env-new))
+(define er-vm-r4-mbox
+  (list
+    (er-mk-tuple (list (er-mk-atom "ok") 1))
+    (er-mk-tuple (list (er-mk-atom "ok") 2))))
+(define er-vm-r4-result
+  (er-vm-dispatch 133 (list er-vm-r1-clauses er-vm-r4-mbox er-vm-r4-env)))
+(er-vm-test "scan first-match wins (index 0)"
+  (get er-vm-r4-result :index) 0)
+(er-vm-test "scan binds first match's var"
+  (get er-vm-r4-env "X") 1)
+
+
+;; ── Phase 9e — OP_SPAWN / OP_SEND ───────────────────────────────
+(er-vm-procs-reset!)
+
+(er-vm-test "spawn opcode by id"
+  (get (er-vm-lookup-opcode-by-id 134) :name) "OP_SPAWN")
+(er-vm-test "send opcode by id"
+  (get (er-vm-lookup-opcode-by-id 135) :name) "OP_SEND")
+
+(define er-vm-fn (fn () "body"))
+(define er-vm-p1 (er-vm-dispatch 134 (list er-vm-fn (list))))
+(define er-vm-p2 (er-vm-dispatch 134 (list er-vm-fn (list "arg"))))
+(er-vm-test "spawn returns pid 0 first"
+  er-vm-p1 0)
+(er-vm-test "spawn returns pid 1 second"
+  er-vm-p2 1)
+(er-vm-test "proc count is 2"
+  (er-vm-proc-count) 2)
+(er-vm-test "spawned proc state runnable"
+  (er-vm-proc-state er-vm-p1) "runnable")
+(er-vm-test "spawned proc mailbox empty"
+  (len (er-vm-proc-mailbox er-vm-p1)) 0)
+(er-vm-test "spawned proc has 8 registers"
+  (len (get (er-vm-proc-get er-vm-p1) :registers)) 8)
+
+;; OP_SEND appends to target's mailbox, preserves arrival order.
+(er-vm-test "send returns true on valid pid"
+  (er-vm-dispatch 135 (list er-vm-p1 "msg1")) true)
+(er-vm-dispatch 135 (list er-vm-p1 "msg2")
+)
+(er-vm-dispatch 135 (list er-vm-p1 "msg3"))
+(er-vm-test "mailbox length after 3 sends"
+  (len (er-vm-proc-mailbox er-vm-p1)) 3)
+(er-vm-test "mailbox preserves order — first"
+  (nth (er-vm-proc-mailbox er-vm-p1) 0) "msg1")
+(er-vm-test "mailbox preserves order — last"
+  (nth (er-vm-proc-mailbox er-vm-p1) 2) "msg3")
+
+;; send to nonexistent pid returns false (doesn't crash)
+(er-vm-test "send to unknown pid is false"
+  (er-vm-dispatch 135 (list 99999 "x")) false)
+
+;; Isolation: msgs to p1 don't appear in p2's mailbox
+(er-vm-test "isolation — p2 mailbox empty"
+  (len (er-vm-proc-mailbox er-vm-p2)) 0)
+
+;; reset clears
+(er-vm-procs-reset!)
+(er-vm-test "reset clears procs"
+  (er-vm-proc-count) 0)
+(er-vm-test "reset resets pid counter"
+  (er-vm-dispatch 134 (list er-vm-fn (list))) 0)
+
+
+;; ── Phase 9f — hot-BIF dispatch table ───────────────────────────
+;; Each opcode skips the registry lookup and calls the underlying
+;; er-bif-* directly. Verify each returns the same result as going
+;; through er-apply-bif.
+
+(er-vm-test "BIF_LENGTH opcode by id"
+  (get (er-vm-lookup-opcode-by-id 136) :name) "OP_BIF_LENGTH")
+(er-vm-test "BIF_LENGTH on 3-cons"
+  (er-vm-dispatch 136
+    (list (er-mk-cons 1 (er-mk-cons 2 (er-mk-cons 3 (er-mk-nil))))))
+  3)
+
+(er-vm-test "BIF_HD on cons"
+  (er-vm-dispatch 137 (list (er-mk-cons 99 (er-mk-nil)))) 99)
+
+(er-vm-test "BIF_TL is cons"
+  (er-cons? (er-vm-dispatch 138
+    (list (er-mk-cons 1 (er-mk-cons 2 (er-mk-nil)))))) true)
+
+(er-vm-test "BIF_ELEMENT pulls index"
+  (er-vm-dispatch 139 (list 2 (er-mk-tuple (list "a" "b" "c")))) "b")
+
+(er-vm-test "BIF_TUPLE_SIZE on 4-tuple"
+  (er-vm-dispatch 140 (list (er-mk-tuple (list 1 2 3 4)))) 4)
+
+(er-vm-test "BIF_LISTS_REVERSE preserves elements"
+  (er-list-length (er-vm-dispatch 141
+    (list (er-mk-cons 1 (er-mk-cons 2 (er-mk-cons 3 (er-mk-nil))))))) 3)
+
+(er-vm-test "BIF_LISTS_REVERSE actually reverses"
+  (get (er-vm-dispatch 141
+    (list (er-mk-cons 1 (er-mk-cons 2 (er-mk-cons 3 (er-mk-nil)))))) :head) 3)
+
+(er-vm-test "BIF_IS_INTEGER true on int"
+  (get (er-vm-dispatch 142 (list 42)) :name) "true")
+(er-vm-test "BIF_IS_INTEGER false on float"
+  (get (er-vm-dispatch 142 (list 3.14)) :name) "false")
+
+(er-vm-test "BIF_IS_ATOM true"
+  (get (er-vm-dispatch 143 (list (er-mk-atom "ok"))) :name) "true")
+(er-vm-test "BIF_IS_ATOM false on int"
+  (get (er-vm-dispatch 143 (list 7)) :name) "false")
+
+(er-vm-test "BIF_IS_LIST true on cons"
+  (get (er-vm-dispatch 144
+    (list (er-mk-cons 1 (er-mk-nil)))) :name) "true")
+(er-vm-test "BIF_IS_LIST true on nil"
+  (get (er-vm-dispatch 144 (list (er-mk-nil))) :name) "true")
+(er-vm-test "BIF_IS_LIST false on tuple"
+  (get (er-vm-dispatch 144 (list (er-mk-tuple (list)))) :name) "false")
+
+(er-vm-test "BIF_IS_TUPLE true"
+  (get (er-vm-dispatch 145 (list (er-mk-tuple (list 1)))) :name) "true")
+(er-vm-test "BIF_IS_TUPLE false on int"
+  (get (er-vm-dispatch 145 (list 5)) :name) "false")
+
+;; Sanity: total opcode count grew (3 patterns + perform + handle +
+;; receive-scan + spawn + send + 10 hot-BIFs = 16+ registered).
+(er-vm-test "opcode list has 16+"
+  (>= (len (er-vm-list-opcodes)) 16) true)
+
+
+;; ── Phase 9i — host opcode-id resolution ────────────────────────
+;; Requires a binary with the erlang_ext extension registered (9h).
+;; The loop runs conformance against exactly that binary.
+(er-vm-test "host id: OP_PATTERN_TUPLE = 222"
+  (er-vm-host-opcode-id "erlang.OP_PATTERN_TUPLE") 222)
+(er-vm-test "host id: OP_BIF_IS_TUPLE = 239"
+  (er-vm-host-opcode-id "erlang.OP_BIF_IS_TUPLE") 239)
+(er-vm-test "host id: unknown name -> nil"
+  (er-vm-host-opcode-id "erlang.OP_NOPE") nil)
+(er-vm-test "effective id prefers host when present"
+  (er-vm-effective-opcode-id "erlang.OP_BIF_LENGTH" 136) 230)
+(er-vm-test "effective id falls back to stub on nil"
+  (er-vm-effective-opcode-id "erlang.OP_NOPE" 999) 999)
+;; The full erlang.OP_* namespace resolves to the contiguous 222-239 block.
+(er-vm-test "host ids contiguous 222..239"
+  (let ((names (list "erlang.OP_PATTERN_TUPLE" "erlang.OP_PATTERN_LIST"
+                     "erlang.OP_PATTERN_BINARY" "erlang.OP_PERFORM"
+                     "erlang.OP_HANDLE" "erlang.OP_RECEIVE_SCAN"
+                     "erlang.OP_SPAWN" "erlang.OP_SEND"
+                     "erlang.OP_BIF_LENGTH" "erlang.OP_BIF_HD"
+                     "erlang.OP_BIF_TL" "erlang.OP_BIF_ELEMENT"
+                     "erlang.OP_BIF_TUPLE_SIZE" "erlang.OP_BIF_LISTS_REVERSE"
+                     "erlang.OP_BIF_IS_INTEGER" "erlang.OP_BIF_IS_ATOM"
+                     "erlang.OP_BIF_IS_LIST" "erlang.OP_BIF_IS_TUPLE"))
+        (ok (list true)))
+    (for-each
+      (fn (i)
+        (when (not (= (er-vm-host-opcode-id (nth names i)) (+ 222 i)))
+          (set-nth! ok 0 false)))
+      (range 0 (len names)))
+    (nth ok 0))
+  true)
+
+(define er-vm-test-summary (str "vm " er-vm-test-pass "/" er-vm-test-count))

lib/erlang/tokenizer.sx

@@ -229,13 +229,37 @@
                 (= ch "$")
                 (do
                   (er-advance! 1)
-                  (if
+                  ;; Emit the char's decimal code as the integer token value
-                    (and (< pos src-len) (= (er-cur) "\\"))
+                  ;; (was: raw "$X" text — parse-number then returned nil).
-                    (do
+                  (let
-                      (er-advance! 1)
+                    ((code (cond
-                      (when (< pos src-len) (er-advance! 1)))
+                       (>= pos src-len) 0
-                    (when (< pos src-len) (er-advance! 1)))
+                       (= (er-cur) "\\")
-                  (er-emit! "integer" (slice src start pos) start)
+                         (do
+                           (er-advance! 1)
+                           (let ((esc (if (< pos src-len) (er-cur) "")))
+                             (when (< pos src-len) (er-advance! 1))
+                             (cond
+                               (= esc "n")  10
+                               (= esc "t")  9
+                               (= esc "r")  13
+                               (= esc "s")  32
+                               (= esc "b")  8
+                               (= esc "e")  27
+                               (= esc "f")  12
+                               (= esc "v")  11
+                               (= esc "d")  127
+                               (= esc "0")  0
+                               (= esc "\\")  92
+                               (= esc "\"") 34
+                               (= esc "'")  39
+                               (= esc "")   0
+                               :else (char->integer (nth (string->list esc) 0)))))
+                       :else
+                         (let ((c (er-cur)))
+                           (er-advance! 1)
+                           (char->integer (nth (string->list c) 0))))))
+                    (er-emit! "integer" (str code) start))
                   (scan!))
                 (er-lower? ch)
                 (do

lib/erlang/transpile.sx

@@ -107,7 +107,12 @@
     (let
       ((ty (get node :type)))
       (cond
-        (= ty "integer") (parse-number (get node :value))
+        (= ty "integer")
+          (let ((n (parse-number (get node :value))))
+            (cond
+              (= n nil) (error (str "Erlang: invalid integer literal: "
+                                     (get node :value)))
+              :else (truncate n)))
         (= ty "float") (parse-number (get node :value))
         (= ty "atom") (er-mk-atom (get node :value))
         (= ty "string") (get node :value)
@@ -669,96 +674,23 @@
 
 (define
   er-apply-bif
-  (fn
+  (fn (name vs)
-    (name vs)
+    (let ((entry (er-lookup-bif "erlang" name (len vs))))
-    (cond
+      (if (not (= entry nil))
-      (= name "is_integer") (er-bif-is-integer vs)
+        ((get entry :fn) vs)
-      (= name "is_atom") (er-bif-is-atom vs)
+        (error (str "Erlang: undefined function '" name "/" (len vs) "'"))))))
-      (= name "is_list") (er-bif-is-list vs)
-      (= name "is_tuple") (er-bif-is-tuple vs)
-      (= name "is_number") (er-bif-is-number vs)
-      (= name "is_float") (er-bif-is-float vs)
-      (= name "is_boolean") (er-bif-is-boolean vs)
-      (= name "length") (er-bif-length vs)
-      (= name "hd") (er-bif-hd vs)
-      (= name "tl") (er-bif-tl vs)
-      (= name "element") (er-bif-element vs)
-      (= name "tuple_size") (er-bif-tuple-size vs)
-      (= name "atom_to_list") (er-bif-atom-to-list vs)
-      (= name "list_to_atom") (er-bif-list-to-atom vs)
-      (= name "is_pid") (er-bif-is-pid vs)
-      (= name "is_reference") (er-bif-is-reference vs)
-      (= name "is_binary") (er-bif-is-binary vs)
-      (= name "byte_size") (er-bif-byte-size vs)
-      (= name "abs") (er-bif-abs vs)
-      (= name "min") (er-bif-min vs)
-      (= name "max") (er-bif-max vs)
-      (= name "tuple_to_list") (er-bif-tuple-to-list vs)
-      (= name "list_to_tuple") (er-bif-list-to-tuple vs)
-      (= name "integer_to_list") (er-bif-integer-to-list vs)
-      (= name "list_to_integer") (er-bif-list-to-integer vs)
-      (= name "is_function") (er-bif-is-function vs)
-      (= name "self") (er-bif-self vs)
-      (= name "spawn") (er-bif-spawn vs)
-      (= name "exit") (er-bif-exit vs)
-      (= name "make_ref") (er-bif-make-ref vs)
-      (= name "link") (er-bif-link vs)
-      (= name "unlink") (er-bif-unlink vs)
-      (= name "monitor") (er-bif-monitor vs)
-      (= name "demonitor") (er-bif-demonitor vs)
-      (= name "process_flag") (er-bif-process-flag vs)
-      (= name "register") (er-bif-register vs)
-      (= name "unregister") (er-bif-unregister vs)
-      (= name "whereis") (er-bif-whereis vs)
-      (= name "registered") (er-bif-registered vs)
-      (= name "throw") (raise (er-mk-throw-marker (er-bif-arg1 vs "throw")))
-      (= name "error") (raise (er-mk-error-marker (er-bif-arg1 vs "error")))
-      :else (error
-        (str "Erlang: undefined function '" name "/" (len vs) "'")))))
 
 (define
   er-apply-remote-bif
-  (fn
+  (fn (mod name vs)
-    (mod name vs)
     (cond
       (dict-has? (er-modules-get) mod)
-      (er-apply-user-module mod name vs)
+        (er-apply-user-module mod name vs)
-      (= mod "lists") (er-apply-lists-bif name vs)
+      :else
-      (= mod "io") (er-apply-io-bif name vs)
+        (let ((entry (er-lookup-bif mod name (len vs))))
-      (= mod "erlang") (er-apply-bif name vs)
+          (if (not (= entry nil))
-      (= mod "ets") (er-apply-ets-bif name vs)
+            ((get entry :fn) vs)
-      :else (error
+            (error (str "Erlang: undefined remote function '" mod ":" name "/" (len vs) "'")))))))
-        (str "Erlang: undefined module '" mod "'")))))
-
-(define
-  er-apply-lists-bif
-  (fn
-    (name vs)
-    (cond
-      (= name "reverse") (er-bif-lists-reverse vs)
-      (= name "map") (er-bif-lists-map vs)
-      (= name "foldl") (er-bif-lists-foldl vs)
-      (= name "seq") (er-bif-lists-seq vs)
-      (= name "sum") (er-bif-lists-sum vs)
-      (= name "nth") (er-bif-lists-nth vs)
-      (= name "last") (er-bif-lists-last vs)
-      (= name "member") (er-bif-lists-member vs)
-      (= name "append") (er-bif-lists-append vs)
-      (= name "filter") (er-bif-lists-filter vs)
-      (= name "any") (er-bif-lists-any vs)
-      (= name "all") (er-bif-lists-all vs)
-      (= name "duplicate") (er-bif-lists-duplicate vs)
-      :else (error
-        (str "Erlang: undefined 'lists:" name "/" (len vs) "'")))))
-
-(define
-  er-apply-io-bif
-  (fn
-    (name vs)
-    (cond
-      (= name "format") (er-bif-io-format vs)
-      :else (error
-        (str "Erlang: undefined 'io:" name "/" (len vs) "'")))))
 
 (define
   er-bif-arg1
@@ -894,16 +826,30 @@
         (len (get v :elements))
         (error "Erlang: tuple_size: not a tuple")))))
 
+(define er-string->charlist
+  (fn (s)
+    (let ((cs (string->list s)) (out (er-mk-nil)))
+      (for-each
+        (fn (i)
+          (set! out (er-mk-cons
+                      (char->integer (nth cs (- (- (len cs) 1) i)))
+                      out)))
+        (range 0 (len cs)))
+      out)))
+
 (define
   er-bif-atom-to-list
   (fn
     (vs)
     (let
       ((v (er-bif-arg1 vs "atom_to_list")))
+      ;; Standard Erlang: atom_to_list/1 returns an Erlang charlist
+      ;; (list of integer char codes). Was: SX string of :name —
+      ;; unusable from Erlang-land for [Char|T] / ++ / binary segments.
       (if
         (er-atom? v)
-        (get v :name)
+        (er-string->charlist (get v :name))
-        (error "Erlang: atom_to_list: not an atom")))))
+        (raise (er-mk-error-marker (er-mk-atom "badarg")))))))
 
 (define
   er-bif-list-to-atom
@@ -911,10 +857,11 @@
     (vs)
     (let
       ((v (er-bif-arg1 vs "list_to_atom")))
-      (if
+      ;; Accept Erlang charlist (cons of ints) or SX string.
-        (= (type-of v) "string")
+      (let ((s (er-source-to-string v)))
-        (er-mk-atom v)
+        (cond
-        (error "Erlang: list_to_atom: not a string")))))
+          (= s nil) (raise (er-mk-error-marker (er-mk-atom "badarg")))
+          :else (er-mk-atom s))))))
 
 ;; ── lists module ─────────────────────────────────────────────────
 (define
@@ -1200,7 +1147,7 @@
         (and (er-atom? ms) (= (get ms :name) "infinity"))
         (er-eval-receive-loop node pid env)
         (= ms 0) (er-eval-receive-poll node pid env)
-        :else (er-eval-receive-timed node pid env)))))
+        :else (er-eval-receive-timed node pid env (+ (er-clock) ms))))))
 
 ;; after 0 — poll once; on no match, run the after-body immediately.
 (define
@@ -1214,12 +1161,15 @@
         (get r :value)
         (er-eval-body (get node :after-body) env)))))
 
-;; after Ms — suspend; on resume check :timed-out. When the scheduler
+;; after Ms — suspend with an absolute `deadline` (logical ms). On
-;; runs out of other work it fires one pending timeout per round.
+;; resume check :timed-out: the scheduler fires the earliest pending
+;; deadline once the runnable queue drains. A non-matching message can
+;; wake the process early; it re-suspends on the SAME deadline so the
+;; timeout window is not extended.
 (define
   er-eval-receive-timed
   (fn
-    (node pid env)
+    (node pid env deadline)
     (let
       ((r (er-try-receive (get node :clauses) pid env)))
       (if
@@ -1227,6 +1177,7 @@
         (get r :value)
         (do
           (er-proc-set! pid :has-timeout true)
+          (er-proc-set! pid :timeout-deadline deadline)
           (call/cc
             (fn
               (k)
@@ -1239,7 +1190,7 @@
               (er-proc-set! pid :timed-out false)
               (er-proc-set! pid :has-timeout false)
               (er-eval-body (get node :after-body) env))
-            (er-eval-receive-timed node pid env)))))))
+            (er-eval-receive-timed node pid env deadline)))))))
 
 ;; Scan mailbox in arrival order. For each msg, try every clause.
 ;; On first match: remove that msg from mailbox and return body value.
@@ -1670,10 +1621,12 @@
     (vs)
     (let
       ((v (er-bif-arg1 vs "integer_to_list")))
+      ;; Standard Erlang: integer_to_list/1 returns an Erlang charlist
+      ;; (e.g. integer_to_list(42) -> [$4, $2] -> [52, 50]).
       (cond
         (not (= (type-of v) "number"))
         (raise (er-mk-error-marker (er-mk-atom "badarg")))
-        :else (str v)))))
+        :else (er-string->charlist (str v))))))
 
 (define
   er-bif-list-to-integer
@@ -1681,15 +1634,14 @@
     (vs)
     (let
       ((v (er-bif-arg1 vs "list_to_integer")))
-      (cond
+      ;; Accept Erlang charlist (cons of ints) or SX string.
-        (not (= (type-of v) "string"))
+      (let ((s (er-source-to-string v)))
-        (raise (er-mk-error-marker (er-mk-atom "badarg")))
+        (cond
-        :else (let
+          (= s nil) (raise (er-mk-error-marker (er-mk-atom "badarg")))
-          ((n (parse-number v)))
+          :else (let ((n (parse-number s)))
-          (cond
+            (cond
-            (= n nil)
+              (= n nil) (raise (er-mk-error-marker (er-mk-atom "badarg")))
-            (raise (er-mk-error-marker (er-mk-atom "badarg")))
+              :else n)))))))
-            :else n))))))
 
 (define
   er-bif-is-function
@@ -1911,3 +1863,180 @@
           (fn (_) (set! out (er-mk-cons v out)))
           (range 0 n))
         out))))
+
+
+;; ── code module (Phase 7 hot-reload) ─────────────────────────────
+(define er-source-walk-bytes!
+  (fn (n bytes-box)
+    (cond
+      (er-nil? n) true
+      (er-cons? n)
+        (let ((h (get n :head)))
+          (cond
+            (= (type-of h) "number")
+              (do (append! (nth bytes-box 0) h)
+                  (er-source-walk-bytes! (get n :tail) bytes-box))
+            :else (do (set-nth! bytes-box 0 nil) false)))
+      :else (do (set-nth! bytes-box 0 nil) false))))
+
+(define er-source-to-string
+  (fn (v)
+    (cond
+      (= (type-of v) "string") v
+      (er-binary? v) (list->string (map integer->char (get v :bytes)))
+      (or (er-nil? v) (er-cons? v))
+        (let ((box (list (list))))
+          (er-source-walk-bytes! v box)
+          (cond
+            (= (nth box 0) nil) nil
+            :else (list->string (map integer->char (nth box 0)))))
+      :else nil)))
+
+(define er-bif-code-load-binary
+  (fn (vs)
+    (let ((mod-arg (nth vs 0)) (src-arg (nth vs 2)))
+      (cond
+        (not (er-atom? mod-arg))
+          (er-mk-tuple (list (er-mk-atom "error") (er-mk-atom "badarg")))
+        :else
+          (let ((src-str (er-source-to-string src-arg)))
+            (cond
+              (= src-str nil)
+                (er-mk-tuple (list (er-mk-atom "error") (er-mk-atom "badarg")))
+              :else
+                (let ((result-box (list nil)) (failed-box (list false)))
+                  (guard
+                    (c (:else (set-nth! failed-box 0 true)))
+                    (set-nth! result-box 0 (erlang-load-module src-str)))
+                  (cond
+                    (nth failed-box 0)
+                      (er-mk-tuple
+                        (list (er-mk-atom "error") (er-mk-atom "badfile")))
+                    (not (= (get (nth result-box 0) :name) (get mod-arg :name)))
+                      (er-mk-tuple
+                        (list (er-mk-atom "error") (er-mk-atom "module_name_mismatch")))
+                    :else
+                      (er-mk-tuple (list (er-mk-atom "module") mod-arg))))))))))
+
+(define er-env-derived-from?
+  (fn (env target-env)
+    ;; Object-identity check, NOT value `=`. On evaluators where dict `=`
+    ;; is structural/deep, comparing closure envs (which are large and
+    ;; cyclic — a module fun's env references the fun) does not terminate.
+    ;; `identical?` is pointer identity on every host and is the actual
+    ;; intended semantics: "is this the same env object".
+    (cond
+      (identical? env target-env) true
+      :else
+        (let ((ks (keys env)) (found-ref (list false)))
+          (for-each
+            (fn (i)
+              (when (not (nth found-ref 0))
+                (let ((v (get env (nth ks i))))
+                  (when (and (er-fun? v) (identical? (get v :env) target-env))
+                    (set-nth! found-ref 0 true)))))
+            (range 0 (len ks)))
+          (nth found-ref 0)))))
+
+(define er-procs-on-env
+  (fn (target-env)
+    (let ((all-keys (keys (er-sched-processes)))
+          (matches (list)))
+      (for-each
+        (fn (i)
+          (let ((proc (get (er-sched-processes) (nth all-keys i))))
+            (let ((init-fun (get proc :initial-fun)))
+              (when (and (not (= init-fun nil))
+                         (er-fun? init-fun)
+                         (er-env-derived-from? (get init-fun :env) target-env)
+                         (not (= (get proc :state) "dead")))
+                (append! matches (get proc :pid))))))
+        (range 0 (len all-keys)))
+      matches)))
+
+(define er-bif-code-purge
+  (fn (vs)
+    (let ((mod-arg (nth vs 0)))
+      (cond
+        (not (er-atom? mod-arg))
+          (raise (er-mk-error-marker (er-mk-atom "badarg")))
+        :else
+          (let ((registry (er-modules-get)) (mod-name (get mod-arg :name)))
+            (cond
+              (not (dict-has? registry mod-name)) (er-mk-atom "false")
+              :else
+                (let ((slot (get registry mod-name)))
+                  (cond
+                    (= (er-module-old-env slot) nil) (er-mk-atom "false")
+                    :else
+                      (let ((procs (er-procs-on-env (er-module-old-env slot))))
+                        (for-each
+                          (fn (i) (er-cascade-exit! (nth procs i) (er-mk-atom "killed")))
+                          (range 0 (len procs)))
+                        (dict-set! registry mod-name
+                          (er-mk-module-slot (er-module-current-env slot) nil
+                            (er-module-version slot)))
+                        (er-mk-atom "true"))))))))))
+
+(define er-bif-code-soft-purge
+  (fn (vs)
+    (let ((mod-arg (nth vs 0)))
+      (cond
+        (not (er-atom? mod-arg))
+          (raise (er-mk-error-marker (er-mk-atom "badarg")))
+        :else
+          (let ((registry (er-modules-get)) (mod-name (get mod-arg :name)))
+            (cond
+              (not (dict-has? registry mod-name)) (er-mk-atom "true")
+              :else
+                (let ((slot (get registry mod-name)))
+                  (cond
+                    (= (er-module-old-env slot) nil) (er-mk-atom "true")
+                    :else
+                      (let ((procs (er-procs-on-env (er-module-old-env slot))))
+                        (cond
+                          (> (len procs) 0) (er-mk-atom "false")
+                          :else
+                            (do
+                              (dict-set! registry mod-name
+                                (er-mk-module-slot (er-module-current-env slot) nil
+                                  (er-module-version slot)))
+                              (er-mk-atom "true"))))))))))))
+
+(define er-bif-code-which
+  (fn (vs)
+    (let ((mod-arg (nth vs 0)))
+      (cond
+        (not (er-atom? mod-arg))
+          (raise (er-mk-error-marker (er-mk-atom "badarg")))
+        (dict-has? (er-modules-get) (get mod-arg :name))
+          (er-mk-atom "loaded")
+        :else (er-mk-atom "non_existing")))))
+
+(define er-bif-code-is-loaded
+  (fn (vs)
+    (let ((mod-arg (nth vs 0)))
+      (cond
+        (not (er-atom? mod-arg))
+          (raise (er-mk-error-marker (er-mk-atom "badarg")))
+        (dict-has? (er-modules-get) (get mod-arg :name))
+          (er-mk-tuple (list (er-mk-atom "file") (er-mk-atom "loaded")))
+        :else (er-mk-atom "false")))))
+
+(define er-bif-code-all-loaded
+  (fn (vs)
+    (let ((registry (er-modules-get))
+          (ks (keys (er-modules-get)))
+          (out (er-mk-nil)))
+      (for-each
+        (fn (i)
+          (let ((k (nth ks (- (- (len ks) 1) i))))
+            (set! out
+              (er-mk-cons
+                (er-mk-tuple
+                  (list (er-mk-atom k) (er-mk-atom "loaded")))
+                out))))
+        (range 0 (len ks)))
+      out)))
+
+

lib/erlang/vm/dispatcher.sx

@@ -0,0 +1,313 @@
+;; Erlang VM — stub opcode dispatcher (Phase 9).
+;;
+;; Mimics the OCaml-side EXTENSION shape from
+;; plans/sx-vm-opcode-extension.md so opcodes 9b-9g can be designed
+;; and tested in SX before 9a (`hosts/ocaml/`) lands the real
+;; registration plumbing. When 9a is available, these stubs become
+;; the cross-host SX-side mirror of the C/OCaml handlers and the
+;; bytecode compiler emits them directly.
+;;
+;; Opcode IDs follow the plan's tier partition:
+;;   0-127     reserved for SX core
+;;   128-199   guest extensions (e.g. erlang, lua)
+;;   200-247   port-/platform-specific
+;;
+;; Erlang owns 128-159 for now.
+
+(define er-vm-opcodes (list {}))
+
+(define er-vm-opcodes-get (fn () (nth er-vm-opcodes 0)))
+
+(define
+  er-vm-opcodes-reset!
+  (fn () (set-nth! er-vm-opcodes 0 {})))
+
+(define
+  er-vm-register-opcode!
+  (fn
+    (id name handler)
+    (dict-set! (er-vm-opcodes-get) (str id) {:name name :id id :handler handler})
+    (er-mk-atom "ok")))
+
+(define
+  er-vm-lookup-opcode-by-id
+  (fn
+    (id)
+    (let
+      ((reg (er-vm-opcodes-get)) (k (str id)))
+      (if (dict-has? reg k) (get reg k) nil))))
+
+(define
+  er-vm-lookup-opcode-by-name
+  (fn
+    (name)
+    (let
+      ((reg (er-vm-opcodes-get))
+        (ks (keys (er-vm-opcodes-get)))
+        (found (list nil)))
+      (for-each
+        (fn
+          (i)
+          (let
+            ((entry (get reg (nth ks i))))
+            (when
+              (= (get entry :name) name)
+              (set-nth! found 0 entry))))
+        (range 0 (len ks)))
+      (nth found 0))))
+
+(define er-vm-list-opcodes (fn () (keys (er-vm-opcodes-get))))
+
+;; ── Phase 9i — host opcode-id resolution ────────────────────────
+;; When the OCaml `erlang_ext` extension is registered (Phase 9h), the
+;; runtime exposes `extension-opcode-id` which maps an "erlang.OP_*"
+;; name to the host-assigned id (222-239). We consult it so the SX
+;; side and the OCaml side agree on ids; when it returns nil (name not
+;; registered) we fall back to the stub-local id.
+;;
+;; NOTE: this requires a binary with the VM extension mechanism (the
+;; vm-ext phase-A..E cherry-pick + Sx_vm_extensions force-link). The
+;; loop builds and runs against exactly that binary
+;; (hosts/ocaml/_build/default/bin/sx_server.exe). `extension-opcode-id`
+;; resolves lazily at call time, so merely loading this file is safe;
+;; only invoking the resolver on a binary that lacks the primitive
+;; would raise.
+
+(define er-vm-host-opcode-id
+  (fn (ext-name)
+    (extension-opcode-id ext-name)))
+
+(define er-vm-effective-opcode-id
+  (fn (ext-name stub-id)
+    (let ((host (extension-opcode-id ext-name)))
+      (cond
+        (= host nil) stub-id
+        :else host))))
+
+(define
+  er-vm-dispatch
+  (fn
+    (id operands)
+    (let
+      ((entry (er-vm-lookup-opcode-by-id id)))
+      (if
+        (= entry nil)
+        (error (str "Erlang VM: unknown opcode id " id))
+        ((get entry :handler) operands)))))
+
+(define
+  er-vm-dispatch-by-name
+  (fn
+    (name operands)
+    (let
+      ((entry (er-vm-lookup-opcode-by-name name)))
+      (if
+        (= entry nil)
+        (error (str "Erlang VM: unknown opcode name '" name "'"))
+        ((get entry :handler) operands)))))
+
+;; ── Phase 9c — effect opcodes (perform / handle) ────────────────
+;; Stub algebraic-effects-style operators. OP_PERFORM raises a tagged
+;; exception; OP_HANDLE wraps a thunk in `guard` and catches matching
+;; effects, passing the args to the handler. The real specialization
+;; (constant-time effect dispatch, single-shot vs multi-shot continuations)
+;; lands when 9a integrates.
+
+(define er-vm-effect-marker?
+  (fn (c effect-name)
+    (and (= (type-of c) "dict")
+         (= (get c :tag) "vm-effect")
+         (= (get c :effect) effect-name))))
+
+(define er-vm-op-perform
+  (fn (operands)
+    (raise {:tag "vm-effect" :effect (nth operands 0) :args (nth operands 1)})))
+
+(define er-vm-op-handle
+  (fn (operands)
+    (let ((thunk (nth operands 0))
+          (effect-name (nth operands 1))
+          (handler (nth operands 2))
+          (result (list nil))
+          (caught (list false))
+          (rethrow (list nil)))
+      (guard
+        (c
+          (:else
+            (cond
+              (er-vm-effect-marker? c effect-name)
+                (do (set-nth! caught 0 true)
+                    (set-nth! result 0 (handler (get c :args))))
+              :else (set-nth! rethrow 0 c))))
+        (set-nth! result 0 (thunk)))
+      (cond
+        (not (= (nth rethrow 0) nil)) (raise (nth rethrow 0))
+        :else (nth result 0)))))
+
+;; ── Phase 9d — receive scan opcode ────────────────────────────
+;; Selective receive primitive. Scans a mailbox value-list in arrival
+;; order; for each value, tries each clause's pattern (binding into
+;; env on success); on match returns `{:matched true :index N :body B}`
+;; — the caller decides what to do with the index (queue-delete) and
+;; the body (eval in the now-mutated env). On miss returns
+;; `{:matched false}`, the caller arranges suspension (via OP_PERFORM).
+;;
+;; Operands: (clauses mbox-list env)
+;;   clauses    — list of {:pattern :guards :body} dicts
+;;   mbox-list  — SX list of message values
+;;   env        — env dict (mutated on match)
+
+(define er-vm-receive-try-clauses
+  (fn (clauses msg env i)
+    (cond
+      (>= i (len clauses)) {:matched false}
+      :else
+        (let ((c (nth clauses i)) (snap (er-env-copy env)))
+          (cond
+            (and
+              (er-match! (get c :pattern) msg env)
+              (er-eval-guards (get c :guards) env))
+              {:matched true :body (get c :body)}
+            :else
+              (do (er-env-restore! env snap)
+                  (er-vm-receive-try-clauses clauses msg env (+ i 1))))))))
+
+(define er-vm-receive-scan-loop
+  (fn (clauses mbox env i)
+    (cond
+      (>= i (len mbox)) {:matched false}
+      :else
+        (let ((msg (nth mbox i))
+              (cr (er-vm-receive-try-clauses clauses msg env 0)))
+          (cond
+            (get cr :matched) {:matched true :index i :body (get cr :body)}
+            :else (er-vm-receive-scan-loop clauses mbox env (+ i 1)))))))
+
+(define er-vm-op-receive-scan
+  (fn (operands)
+    (er-vm-receive-scan-loop (nth operands 0) (nth operands 1) (nth operands 2) 0)))
+
+;; ── Phase 9e — spawn / send + lightweight scheduler ─────────────
+;; Stub register-machine process layout for the eventual fast scheduler.
+;; A VM-process is `{:id :registers :mailbox :state :initial-fn :initial-args}`.
+;; Registers is a vector (SX list, mutated via set-nth!) — fixed slot count
+;; per process so cells don't grow during execution. Mailbox is an SX list.
+;; State is one of "runnable" / "waiting" / "dead". This sits PARALLEL to
+;; the existing `er-scheduler` (which is the language-level scheduler) —
+;; the VM scheduler will eventually take over once 9a integrates and
+;; bytecode-compiled Erlang runs against it.
+
+(define er-vm-procs (list {}))
+(define er-vm-procs-get (fn () (nth er-vm-procs 0)))
+(define er-vm-procs-reset!
+  (fn () (do (set-nth! er-vm-procs 0 {}) (set-nth! er-vm-next-pid 0 0))))
+
+(define er-vm-next-pid (list 0))
+
+(define er-vm-proc-new!
+  (fn (initial-fn initial-args)
+    (let ((pid (nth er-vm-next-pid 0)))
+      (set-nth! er-vm-next-pid 0 (+ pid 1))
+      (let ((proc
+              {:id pid
+               :registers (list nil nil nil nil nil nil nil nil)
+               :mailbox (list)
+               :state "runnable"
+               :initial-fn initial-fn
+               :initial-args initial-args}))
+        (dict-set! (er-vm-procs-get) (str pid) proc)
+        pid))))
+
+(define er-vm-proc-get (fn (pid) (get (er-vm-procs-get) (str pid))))
+
+(define er-vm-proc-send!
+  (fn (pid msg)
+    (let ((proc (er-vm-proc-get pid)))
+      (cond
+        (= proc nil) false
+        :else
+          (do
+            (dict-set! proc :mailbox (append (get proc :mailbox) (list msg)))
+            (when (= (get proc :state) "waiting")
+              (dict-set! proc :state "runnable"))
+            true)))))
+
+(define er-vm-proc-mailbox (fn (pid) (get (er-vm-proc-get pid) :mailbox)))
+(define er-vm-proc-state (fn (pid) (get (er-vm-proc-get pid) :state)))
+(define er-vm-proc-count (fn () (len (keys (er-vm-procs-get)))))
+
+(define er-vm-op-spawn
+  (fn (operands)
+    (er-vm-proc-new! (nth operands 0) (nth operands 1))))
+
+(define er-vm-op-send
+  (fn (operands)
+    (er-vm-proc-send! (nth operands 0) (nth operands 1))))
+
+;; ── Phase 9f — hot-BIF dispatch table ──────────────────────────
+;; Specialized opcodes for the BIFs that the bytecode compiler emits
+;; on hot call sites. The handler is the underlying `er-bif-*` impl
+;; directly — same `(vs)` signature as the dispatcher uses for
+;; operands, so the cost is the opcode-id → handler hop with no
+;; registry-key string lookup. Cold BIFs continue going through the
+;; general path (`er-apply-bif` / `er-lookup-bif`).
+;;
+;; Opcodes 136-159 reserved for hot BIFs.
+
+;; ── Phase 9b — pattern-match opcodes ────────────────────────────
+;; Each handler takes a list (pattern-ast value env) and returns
+;; true/false, mutating env on success (same contract as the
+;; existing er-match-tuple / er-match-cons / er-match-binary).
+;; Wire these as wrappers for now; the real opcodes will eventually
+;; have register-machine semantics and skip the AST-walk overhead.
+
+(define
+  er-vm-register-erlang-opcodes!
+  (fn
+    ()
+    (er-vm-register-opcode!
+      128
+      "OP_PATTERN_TUPLE"
+      (fn
+        (operands)
+        (er-match-tuple
+          (nth operands 0)
+          (nth operands 1)
+          (nth operands 2))))
+    (er-vm-register-opcode!
+      129
+      "OP_PATTERN_LIST"
+      (fn
+        (operands)
+        (er-match-cons
+          (nth operands 0)
+          (nth operands 1)
+          (nth operands 2))))
+    (er-vm-register-opcode!
+      130
+      "OP_PATTERN_BINARY"
+      (fn
+        (operands)
+        (er-match-binary
+          (nth operands 0)
+          (nth operands 1)
+          (nth operands 2))))
+    (er-vm-register-opcode! 131 "OP_PERFORM" er-vm-op-perform)
+    (er-vm-register-opcode! 132 "OP_HANDLE" er-vm-op-handle)
+    (er-vm-register-opcode! 133 "OP_RECEIVE_SCAN" er-vm-op-receive-scan)
+    (er-vm-register-opcode! 134 "OP_SPAWN" er-vm-op-spawn)
+    (er-vm-register-opcode! 135 "OP_SEND" er-vm-op-send)
+    ;; Phase 9f — hot BIFs
+    (er-vm-register-opcode! 136 "OP_BIF_LENGTH"        er-bif-length)
+    (er-vm-register-opcode! 137 "OP_BIF_HD"            er-bif-hd)
+    (er-vm-register-opcode! 138 "OP_BIF_TL"            er-bif-tl)
+    (er-vm-register-opcode! 139 "OP_BIF_ELEMENT"       er-bif-element)
+    (er-vm-register-opcode! 140 "OP_BIF_TUPLE_SIZE"    er-bif-tuple-size)
+    (er-vm-register-opcode! 141 "OP_BIF_LISTS_REVERSE" er-bif-lists-reverse)
+    (er-vm-register-opcode! 142 "OP_BIF_IS_INTEGER"    er-bif-is-integer)
+    (er-vm-register-opcode! 143 "OP_BIF_IS_ATOM"       er-bif-is-atom)
+    (er-vm-register-opcode! 144 "OP_BIF_IS_LIST"       er-bif-is-list)
+    (er-vm-register-opcode! 145 "OP_BIF_IS_TUPLE"      er-bif-is-tuple)
+    (er-mk-atom "ok")))
+
+(er-vm-register-erlang-opcodes!)

next/.gitignore

@@ -0,0 +1 @@
+data/

next/README.md

@@ -0,0 +1,170 @@
+# next — fed-sx Milestone 1 kernel
+
+Single-instance, single-actor fed-sx server built as Erlang-on-SX modules.
+See `plans/fed-sx-design.md` for the architecture and
+`plans/fed-sx-milestone-1.md` for the build plan + per-step progress log.
+
+## Status
+
+Both Step 9 smoke proof points are functional **in-process**:
+
+- **9a-pure (verb extensibility)** — `Create{DefineActivity{Pin}}` registers Pin
+  at runtime; subsequent `Pin{path, cid}` activities fold into a pin-state
+  projection. Zero kernel code between definition and use.
+  See `next/tests/smoke_pin_pure.sh`.
+- **9b-pure (reactive application)** — A trigger projection matches Notes
+  tagged `smoketest` and derives a `TestEcho` carrying the source CID.
+  See `next/tests/smoke_app_pure.sh`.
+
+The remaining `9a-tcp` / `9b-tcp` deliverables layer TCP transport on top — see
+*Substrate gaps* below.
+
+## Layout
+
+```
+next/
+├── kernel/      Erlang-on-SX kernel modules (.erl)
+├── genesis/     SX source files for the bootstrap bundle
+├── tests/       Bash test scripts driving sx_server.exe via the epoch protocol
+└── data/        Runtime state — gitignored
+```
+
+## Module map
+
+| Module                | Role                                                                   |
+|-----------------------|------------------------------------------------------------------------|
+| `nx_cid.erl`          | Canonical CID wrapper around the host `cid:to_string` BIF              |
+| `envelope.erl`        | Activity envelope shape, canonical bytes, time-aware sig verify        |
+| `log.erl`             | Per-actor in-memory append log (open / append / tip / replay / entries) |
+| `registry.erl`        | Pure-functional + gen_server-wrapped registry keyed by Kind             |
+| `pipeline.erl`        | Validation driver + stage_envelope/signature/replay/schema             |
+| `projection.erl`      | Pure projection driver + gen_server-per-projection wrapper             |
+| `outbox.erl`          | Envelope construct + sign + publish orchestrator + broadcast            |
+| `bootstrap.erl`       | Genesis read/build/verify/load + one-call `start/3` kernel bring-up    |
+| `define_registry.erl` | Meta-projection fold for `Create{Define*}` → registry                  |
+| `sandbox.erl`         | `eval_pure/2,3` try/catch envelope for projection folds                |
+| `nx_kernel.erl`       | Long-lived runtime orchestrator; per-actor bucketed state (m2 Step 1a)  |
+| `http_server.erl`     | route/1,2 + format-aware GET + POST + Accept header content negotiation |
+
+## Genesis bundle
+
+`next/genesis/` contains 31 SX files across 7 sections, all consumed as data
+(read + serialised by `bootstrap:populate_registry`, not eval'd):
+
+- 3 activity-types — Create, Update, Delete
+- 10 object-types — SXArtifact, Note, Tombstone, 6 Define* meta-types, Snapshot
+- 7 projections — activity-log, by-type, by-actor, by-object, actor-state,
+  define-registry, audience-graph
+- 3 validators — envelope-shape, signature, type-schema
+- 3 codecs — dag-cbor, raw, dag-json
+- 2 sig-suites — rsa-sha256-2018, ed25519-2020
+- 3 audience predicates — Public, Followers, Direct
+
+`manifest.sx` is the bundle root, listed in dependency-friendly order.
+
+## Tests
+
+43 test suites, ~560+ assertions. Each script drives `sx_server.exe` via the
+epoch protocol — loads the Erlang substrate, loads relevant kernel modules
+via `code:load_binary` / `erlang-load-module`, then exercises behaviour
+through `erlang-eval-ast`.
+
+Conventions:
+
+- Scripts marked `_pure.sh` exercise pure-functional state.
+- Scripts marked `_server.sh` (or no suffix) exercise gen_server APIs and
+  must inline `start_link` with operations — the Erlang-on-SX scheduler
+  doesn't preserve spawned processes across separate `erlang-eval-ast`
+  invocations.
+- `smoke_*_pure.sh` are end-to-end smoke tests demonstrating the §Step 9
+  proof points without TCP / curl / JSON.
+
+The Erlang-on-SX conformance gate (`bash lib/erlang/conformance.sh`, **729 /
+729**) is the no-regression contract — every commit on `loops/fed-sx-m1`
+preserves it.
+
+## Substrate
+
+Each `.erl` source file is hot-loaded at boot via
+`code:load_binary(Mod, Filename, SourceString)` (Phase 7 BIF). Tests drive
+the runtime via the epoch protocol:
+
+```bash
+printf '(epoch 1)\n(load "lib/erlang/runtime.sx")\n(epoch 2)\n<test-expr>\n' \
+  | hosts/ocaml/_build/default/bin/sx_server.exe
+```
+
+The kernel calls into these host primitives: `crypto:hash/2`,
+`cid:from_bytes/1`, `cid:to_string/1`, `file:read_file/1`, `file:write_file/2`,
+`file:delete/1`, `file:list_dir/1`, `code:load_binary/3`, plus `http:listen/2`
+(the briefing's allowed scope exception, added to `lib/erlang/runtime.sx`).
+
+### Substrate gaps (parked work)
+
+These three gaps block the remaining unchecked deliverables:
+
+1. **Term codec** (`3b`/`3c`) — **all three substrate fixes done 2026-06-05:**
+   `erlang:binary_to_list/1` and `erlang:list_to_binary/1` registered in
+   `lib/erlang/runtime.sx` (iolist-aware); the tokenizer's `$X` branch
+   emits the decimal char code; `atom_to_list/1` and `integer_to_list/1`
+   now return Erlang charlists (standard Erlang semantics) with `list_to_atom`/
+   `list_to_integer` accepting both charlists and SX strings for back-compat.
+   759/759 conformance. The full term-codec primitive set is in place —
+   Step 3b on-disk segment writer can encode arbitrary Erlang activity
+   terms (atoms, ints, binaries, tuples, lists) into byte sequences using
+   only Erlang-native primitives.
+
+2. **SX-source eval bridge** — There's no BIF that lets Erlang call into the
+   SX evaluator on a parsed source string. Blocks evaluating the `:schema` /
+   `:fold` / `:predicate` / `:verify` bodies from the genesis bundle. Erlang-fun
+   stand-ins (`pipeline:stage_schema`, `define_registry:fold`, etc.) prove the
+   API shapes; the bridge would let bundle bodies dispatch through them
+   unchanged.
+
+3. **Dict ↔ proplist marshalling for `http:listen/2`** — **done 2026-06-05.**
+   `er-bif-http-listen` marshals the native server's request dict
+   (`{:method :path :query :headers :body}`) into the proplist shape
+   `[{method, Bin}, {path, Bin}, {query, Bin}, {headers, [{Name, Value}]},
+   {body, Bin}]` that `http_server:route/2` consumes, and converts the
+   handler's response proplist back to `{:status :headers :body}` for the
+   native server to serialise. Helpers (`er-request-dict-to-proplist`,
+   `er-proplist-to-dict`, `er-of-sx-deep`, `er-to-sx-deep`,
+   `er-dict-to-header-proplist`, `er-proplist-fill!`) live alongside the
+   BIF wrapper in `lib/erlang/runtime.sx`. The BIF also spawns the handler
+   into a real Erlang process via `er-spawn-fun` + `er-sched-run-all!`
+   so `self()` / `gen_server:call` work inside route handlers (the kernel
+   and projection gen_servers reach the handler this way). Verified by
+   `next/tests/http_marshal.sh` and the live TCP smoke
+   `next/tests/http_server_tcp.sh` / `http_server_start.sh`. Unblocks
+   `Step 8b-start` (TCP listener spawn) and the curl-driven 9a-tcp / 9b-tcp
+   smoke tests.
+
+### Bringing up the kernel
+
+For tests, `bootstrap:start/3(ActorId, KeySpec, ActorState)` is the
+one-call boot:
+
+```erlang
+KM = <<1,2,3,4>>,
+KS = [{key_id, k1}, {algorithm, ed25519}, {value, KM}],
+AS = [{public_keys, [[{id, k1}, {created, 0}, {value, KM}]]}],
+Pid = bootstrap:start(alice, KS, AS),
+%% nx_kernel + registry populated; you now have a kernel.
+```
+
+The HTTP layer (`http_server`) and `nx_kernel:publish/1` flow through the
+same in-process gen_servers; `http_publish_fold.sh` is the end-to-end proof
+the chain works.
+
+## What's next (when work resumes)
+
+In priority order:
+
+1. **8b-start** — `http_server:start/1` spawns a process hosting `http:listen/2`.
+   (8b-bridge done — see Substrate gap #3.)
+2. **9a-tcp / 9b-tcp** — replace the in-process smoke scripts with curl-driven
+   versions hitting the running server.
+3. **Term codec / on-disk log** — needs either a new BIF or a temp-file
+   workaround; current in-memory log keeps everything functional otherwise.
+4. **SX-source eval bridge** — unlocks real `:schema` / `:fold` body
+   evaluation from the genesis bundle.

next/genesis/activity-types/announce.sx

@@ -0,0 +1,14 @@
+;; next/genesis/activity-types/announce.sx
+;;
+;; Bootstrap definition of the Announce verb per design §13.5 / m2
+;; Step 11. An Announce re-broadcasts a peer's activity to the
+;; announcer's followers: the announcer's outbox carries an Announce
+;; envelope whose :object is the original activity's CID. Followers
+;; can re-fetch the wrapped activity from the original instance if
+;; their projection wants to fold the body.
+
+(DefineActivity
+  :name "Announce"
+  :doc "Re-broadcast a peer's activity to followers. :object is the CID of the activity being announced. Recipients see the Announce in their inbox / feed; their projection decides whether to fetch the wrapped activity body."
+  :schema (fn (act) (string? (-> act :object)))
+  :semantics (fn (state act) state))

next/genesis/activity-types/create.sx

@@ -0,0 +1,15 @@
+;; next/genesis/activity-types/create.sx
+;;
+;; Bootstrap definition of the Create verb per design §3 and §12.2.
+;; Read as data by the bundler (bootstrap.erl) — never evaluated as
+;; code. The :schema and :semantics bodies are SX source; the
+;; validation pipeline (Step 6) and projection scheduler (Step 7)
+;; evaluate them at the appropriate times.
+
+(DefineActivity
+  :name "Create"
+  :doc "Publish a new object. Required for actor onboarding and for\n        every Define* meta-activity. The activity's :object holds\n        the canonical content of the published object."
+  :schema (fn
+    (act)
+    (and (not (nil? (-> act :object))) (string? (-> act :object :type))))
+  :semantics (fn (state act) state))

next/genesis/activity-types/delete.sx

@@ -0,0 +1,13 @@
+;; next/genesis/activity-types/delete.sx
+;;
+;; Bootstrap definition of the Delete verb per design §3 and §12.2.
+;; Read as data by the bundler — never evaluated as code here. The
+;; :schema and :semantics bodies are SX source; the validator
+;; pipeline (Step 6) and projection scheduler (Step 7) evaluate them
+;; at the appropriate times.
+
+(DefineActivity
+  :name "Delete"
+  :doc "Tombstone an existing object. :object is the CID of the\n        target. Projections fold Delete by removing the object from\n        their working indexes; the underlying log line is never\n        erased — durability of the historical record is independent\n        of projection state."
+  :schema (fn (act) (string? (-> act :object)))
+  :semantics (fn (state act) state))

next/genesis/activity-types/endorse.sx

@@ -0,0 +1,13 @@
+;; next/genesis/activity-types/endorse.sx
+;;
+;; Bootstrap definition of the Endorse verb per design §13.5 / m2
+;; Step 11. An Endorse expresses cross-actor signal on a target
+;; activity (like / share / etc.). :object is the target activity's
+;; CID; :kind is the endorsement variant (string). Projections
+;; aggregate endorsements into counters / heat / ranking signals.
+
+(DefineActivity
+  :name "Endorse"
+  :doc "Cross-actor signal on a target activity. :object is the target activity's CID; :kind is the endorsement variant (e.g. 'like', 'share'). Projections aggregate endorsements into counters / heat / ranking signals."
+  :schema (fn (act) (and (string? (-> act :object)) (string? (-> act :kind))))
+  :semantics (fn (state act) state))

next/genesis/activity-types/update.sx

@@ -0,0 +1,15 @@
+;; next/genesis/activity-types/update.sx
+;;
+;; Bootstrap definition of the Update verb per design §3 and §12.2.
+;; Read as data by the bundler — never evaluated as code here. The
+;; :schema and :semantics bodies are SX source; the validator
+;; pipeline (Step 6) and projection scheduler (Step 7) evaluate them
+;; at the appropriate times.
+
+(DefineActivity
+  :name "Update"
+  :doc "Patch or replace an existing object. :object is the CID of\n        the target; :patch is the field-level edit. Behaviour is\n        delegated to per-object-type semantics — e.g. an Update of a\n        DefineActivity supersedes the prior registry entry; an\n        Update of a Person actor rotates keys via :patch :add-publicKey\n        + :patch :supersede."
+  :schema (fn
+    (act)
+    (and (string? (-> act :object)) (not (nil? (-> act :patch)))))
+  :semantics (fn (state act) state))

next/genesis/audience/direct.sx

@@ -0,0 +1,14 @@
+;; next/genesis/audience/direct.sx
+;;
+;; Direct audience: an actor is a member iff they are
+;; explicitly named in the activity's :to or :cc lists. No
+;; group expansion — true direct addressing only.
+
+(DefineAudience
+  :name "Direct"
+  :doc "Direct-addressing predicate. Tests literal membership\n        in the activity's :to or :cc."
+  :member-of (fn
+    (actor audience)
+    (or
+      (member? actor (-> audience :to))
+      (member? actor (-> audience :cc)))))

next/genesis/audience/followers.sx

@@ -0,0 +1,14 @@
+;; next/genesis/audience/followers.sx
+;;
+;; Followers audience: an actor is a member iff they appear in
+;; the audience-owner's :followers set in the audience-graph
+;; projection. Federation (m2) wires this to peer delivery.
+
+(DefineAudience
+  :name "Followers"
+  :doc "Followers-of-owner predicate. Looks up the\n        audience-graph projection's :followers list for the\n        audience owner and tests membership."
+  :member-of (fn
+    (actor audience)
+    (member?
+      actor
+      (-> (get-projection :audience-graph) (-> audience :owner) :followers))))

next/genesis/audience/public.sx

@@ -0,0 +1,9 @@
+;; next/genesis/audience/public.sx
+;;
+;; Public audience: every actor is a member. Maps to the AP
+;; magic id `https://www.w3.org/ns/activitystreams#Public`.
+
+(DefineAudience
+  :name "Public"
+  :doc "Public audience predicate. Always returns true — every\n        actor on the network is considered a member."
+  :member-of (fn (actor audience) true))

next/genesis/codecs/dag-cbor.sx

@@ -0,0 +1,13 @@
+;; next/genesis/codecs/dag-cbor.sx
+;;
+;; Canonical CBOR encoding per IPLD dag-cbor. Used to compute
+;; envelope canonical bytes for signature coverage and to serialise
+;; the genesis bundle itself. In Erlang-on-SX mode the kernel
+;; dispatches to the host cid:to_string substrate (Step 1b) when
+;; this codec is requested.
+
+(DefineCodec
+  :name "dag-cbor"
+  :doc "Deterministic CBOR with dag-cbor restrictions: sorted\n        map keys, no floats unless required, no indefinite-length\n        items. The canonical wire format for fed-sx artifacts."
+  :encode (fn (term) (host-codec :dag-cbor :encode term))
+  :decode (fn (bytes) (host-codec :dag-cbor :decode bytes)))

next/genesis/codecs/dag-json.sx

@@ -0,0 +1,12 @@
+;; next/genesis/codecs/dag-json.sx
+;;
+;; JSON encoding with dag-json restrictions per IPLD: sorted map
+;; keys, no NaN / Infinity, no comments, CIDs as `{"/": "..."}`.
+;; Used as the human-readable wire format for ActivityPub interop
+;; (JSON-LD over dag-json).
+
+(DefineCodec
+  :name "dag-json"
+  :doc "Deterministic JSON with dag-json restrictions. Sorted\n        keys, CIDs as the {\"/\": \"...\"} object. Used by the\n        HTTP server (Step 8) for application/json responses."
+  :encode (fn (term) (host-codec :dag-json :encode term))
+  :decode (fn (bytes) (host-codec :dag-json :decode bytes)))

next/genesis/codecs/raw.sx

@@ -0,0 +1,12 @@
+;; next/genesis/codecs/raw.sx
+;;
+;; Identity codec — input bytes pass through unchanged in both
+;; directions. Used for already-encoded payloads and for binary
+;; artifacts (images, archives) whose CID is computed over the
+;; raw bytes directly.
+
+(DefineCodec
+  :name "raw"
+  :doc "Identity codec. The CID's multicodec byte is 0x55.\n        :encode and :decode return their input unchanged."
+  :encode (fn (bytes) bytes)
+  :decode (fn (bytes) bytes))

next/genesis/manifest.sx

@@ -0,0 +1,51 @@
+;; next/genesis/manifest.sx
+;;
+;; Genesis bundle root per design §12.2. Lists every definition file
+;; that gets packed into the bundle. The bundler (bootstrap.erl)
+;; walks this manifest, reads each referenced file, parses its
+;; top-level form, and inserts it into the bundle dict at the
+;; appropriate section path.
+;;
+;; The bundle CID is the content-address of the resulting dag-cbor
+;; (or v1 stand-in) blob over the assembled dict. That CID is
+;; baked into the kernel at build time and re-verified on startup
+;; per design §12.3.
+;;
+;; Section values are bare parenthesised paths (data lists, not
+;; function calls) — the manifest is consumed by `parse`, not
+;; `eval`. Empty sections are written as `()`.
+
+(GenesisManifest
+  :version "0.0.1"
+  :kernel-version "1.0.0-m1"
+  :activity-types ("activity-types/create.sx"
+    "activity-types/update.sx"
+    "activity-types/delete.sx"
+    "activity-types/announce.sx"
+    "activity-types/endorse.sx")
+  :object-types ("object-types/sx-artifact.sx"
+    "object-types/note.sx"
+    "object-types/tombstone.sx"
+    "object-types/person.sx"
+    "object-types/service.sx"
+    "object-types/group.sx"
+    "object-types/define-activity.sx"
+    "object-types/define-object.sx"
+    "object-types/define-projection.sx"
+    "object-types/define-validator.sx"
+    "object-types/define-codec.sx"
+    "object-types/define-sig-suite.sx"
+    "object-types/snapshot.sx")
+  :projections ("projections/activity-log.sx"
+    "projections/by-type.sx"
+    "projections/by-actor.sx"
+    "projections/by-object.sx"
+    "projections/actor-state.sx"
+    "projections/define-registry.sx"
+    "projections/audience-graph.sx")
+  :validators ("validators/envelope-shape.sx"
+    "validators/signature.sx"
+    "validators/type-schema.sx")
+  :codecs ("codecs/dag-cbor.sx" "codecs/raw.sx" "codecs/dag-json.sx")
+  :sig-suites ("sig-suites/rsa-sha256-2018.sx" "sig-suites/ed25519-2020.sx")
+  :audience ("audience/public.sx" "audience/followers.sx" "audience/direct.sx"))

next/genesis/object-types/define-activity.sx

@@ -0,0 +1,12 @@
+;; next/genesis/object-types/define-activity.sx
+;;
+;; Meta-object that registers a new activity verb. Published as
+;; Create{DefineActivity{...}}; the define-registry projection
+;; folds it into the activity-types registry. Per design §5.
+
+(DefineObject
+  :name "DefineActivity"
+  :doc "Activity-type registration. :name is the verb (e.g.\n        \"Pin\"); :schema is an SX predicate over activity\n        envelopes; :semantics is an optional state-fold body."
+  :schema (fn
+    (obj)
+    (and (string? (-> obj :name)) (not (nil? (-> obj :schema))))))

next/genesis/object-types/define-codec.sx

@@ -0,0 +1,15 @@
+;; next/genesis/object-types/define-codec.sx
+;;
+;; Meta-object that registers a content codec — an encode/decode
+;; pair. The bootstrap bundle ships dag-cbor, raw, and dag-json
+;; codecs; new codecs can be added via Create{DefineCodec{...}}.
+
+(DefineObject
+  :name "DefineCodec"
+  :doc "Codec registration. :name identifies the codec ('dag-cbor',\n        'raw', 'dag-json', ...); :encode and :decode are the\n        SX bodies the kernel calls when serialising / parsing\n        artifacts under this codec."
+  :schema (fn
+    (obj)
+    (and
+      (string? (-> obj :name))
+      (not (nil? (-> obj :encode)))
+      (not (nil? (-> obj :decode))))))

next/genesis/object-types/define-object.sx

@@ -0,0 +1,12 @@
+;; next/genesis/object-types/define-object.sx
+;;
+;; Meta-object that registers a new object-type. Bootstrap-level —
+;; runtime registration of new object types (e.g. DefineSubscription
+;; in the Step 9b smoke test) flows through this.
+
+(DefineObject
+  :name "DefineObject"
+  :doc "Object-type registration. :name is the type tag (e.g.\n        \"PinSpec\"); :schema is an SX predicate over object\n        forms of that type."
+  :schema (fn
+    (obj)
+    (and (string? (-> obj :name)) (not (nil? (-> obj :schema))))))

next/genesis/object-types/define-projection.sx

@@ -0,0 +1,16 @@
+;; next/genesis/object-types/define-projection.sx
+;;
+;; Meta-object that registers a new projection. The projection
+;; scheduler (Step 7) spawns one gen_server per registered
+;; projection and feeds activities through its :fold body in
+;; sandbox mode.
+
+(DefineObject
+  :name "DefineProjection"
+  :doc "Projection registration. :name is the projection key;\n        :initial-state is the empty state value; :fold is the\n        pure (state activity) -> state function evaluated in\n        sandbox mode per activity."
+  :schema (fn
+    (obj)
+    (and
+      (string? (-> obj :name))
+      (not (nil? (-> obj :initial-state)))
+      (not (nil? (-> obj :fold))))))

next/genesis/object-types/define-sig-suite.sx

@@ -0,0 +1,12 @@
+;; next/genesis/object-types/define-sig-suite.sx
+;;
+;; Meta-object that registers a signature suite. Bootstrap ships
+;; rsa-sha256-2018 and ed25519-2020; the suite name maps an
+;; algorithm to a :verify body and a :key-format predicate.
+
+(DefineObject
+  :name "DefineSigSuite"
+  :doc "Signature suite registration. :name identifies the suite\n        ('rsa-sha256-2018', 'ed25519-2020', ...); :verify is the\n        SX (canonical-bytes signature key) -> bool body; the\n        envelope-signature validator dispatches by suite name."
+  :schema (fn
+    (obj)
+    (and (string? (-> obj :name)) (not (nil? (-> obj :verify))))))

next/genesis/object-types/define-validator.sx

@@ -0,0 +1,12 @@
+;; next/genesis/object-types/define-validator.sx
+;;
+;; Meta-object that registers a validator predicate. The validation
+;; pipeline (Step 6) consults registered validators by name when
+;; running its stages.
+
+(DefineObject
+  :name "DefineValidator"
+  :doc "Validator registration. :name is the validator key (e.g.\n        \"envelope-shape\"); :predicate is the SX (activity) ->\n        ok|{error, R} body."
+  :schema (fn
+    (obj)
+    (and (string? (-> obj :name)) (not (nil? (-> obj :predicate))))))

next/genesis/object-types/group.sx

@@ -0,0 +1,11 @@
+;; next/genesis/object-types/group.sx
+;;
+;; Per design §9.1: a Group is a multi-controller actor — typically
+;; a working group, channel, or collective whose membership is
+;; managed via Add/Remove activities. Sig-suite validation honours
+;; the current key-set rather than a single keypair.
+
+(DefineObject
+  :name "Group"
+  :doc "Multi-controller actor. :name is the group's display name; :preferredUsername is the local handle; :summary is the description; :icon is a CID or URL; :members is the current member list (managed via Add/Remove)."
+  :schema (fn (obj) (string? (-> obj :name))))

next/genesis/object-types/note.sx

@@ -0,0 +1,10 @@
+;; next/genesis/object-types/note.sx
+;;
+;; Short message intended for an audience, ActivityPub-Note-compatible.
+;; Used by the Step 9b reactive smoke test (Note tagged "smoketest"
+;; matches the Topic subscription).
+
+(DefineObject
+  :name "Note"
+  :doc "Short authored message. :content is the body text;\n        :tags is a list of subscription-routable tags."
+  :schema (fn (obj) (string? (-> obj :content))))

next/genesis/object-types/person.sx

@@ -0,0 +1,11 @@
+;; next/genesis/object-types/person.sx
+;;
+;; Per design §9.1: a Person is the canonical actor type for a
+;; human-controlled identity. Bootstrapped via Create{Person{...}}
+;; as the actor's first activity (see nx_kernel:bootstrap_actor/4).
+;; ActivityPub-Person-compatible.
+
+(DefineObject
+  :name "Person"
+  :doc "Human-controlled actor. :name is the display name; :preferredUsername is the local handle; :summary is the profile bio; :icon is a CID or URL."
+  :schema (fn (obj) (string? (-> obj :name))))

next/genesis/object-types/service.sx

@@ -0,0 +1,11 @@
+;; next/genesis/object-types/service.sx
+;;
+;; Per design §9.1: a Service is a non-human actor — a bot, an
+;; automated feed, an organisational publisher. Same activity
+;; surface as Person, different ActivityPub Actor type. Tooling
+;; treats a Service identically to a Person except for UX hints.
+
+(DefineObject
+  :name "Service"
+  :doc "Automated / programmatic actor. :name is the display name; :preferredUsername is the local handle; :summary is the profile bio; :icon is a CID or URL."
+  :schema (fn (obj) (string? (-> obj :name))))

next/genesis/object-types/snapshot.sx

@@ -0,0 +1,13 @@
+;; next/genesis/object-types/snapshot.sx
+;;
+;; Projection state checkpoint. The projection scheduler emits
+;; Snapshot{projection-name, state-cid, log-seq} periodically;
+;; cold starts read the most recent Snapshot and replay only
+;; activities after :log-seq. Per design §10.5.
+
+(DefineObject
+  :name "Snapshot"
+  :doc "Projection-state checkpoint. :projection-name identifies\n        the projection; :state-cid is the content-address of\n        the snapshotted state value; :log-seq is the activity\n        sequence number the snapshot was taken at."
+  :schema (fn
+    (obj)
+    (and (string? (-> obj :projection-name)) (string? (-> obj :state-cid)))))

next/genesis/object-types/sx-artifact.sx

@@ -0,0 +1,10 @@
+;; next/genesis/object-types/sx-artifact.sx
+;;
+;; Content-addressed SX source — a library, component, or
+;; executable form published via Create{SXArtifact{...}}.
+;; Consumers reference an artifact by its CID. Per design §3.4.
+
+(DefineObject
+  :name "SXArtifact"
+  :doc "Published SX source. :source carries the form text;\n        :language is optional ('sx' by default); :imports lists\n        CIDs the artifact depends on."
+  :schema (fn (obj) (string? (-> obj :source))))

next/genesis/object-types/tombstone.sx

@@ -0,0 +1,9 @@
+;; next/genesis/object-types/tombstone.sx
+;;
+;; Replacement for an object that has been Delete'd. Lets projection
+;; folds keep a marker without retaining the deleted content.
+
+(DefineObject
+  :name "Tombstone"
+  :doc "Marker for a deleted object. :former-cid carries the CID\n        of the object that was removed. Projections fold Tombstone\n        by replacing the cached entry (not by omitting it)."
+  :schema (fn (obj) (string? (-> obj :former-cid))))

next/genesis/projections/activity-log.sx

@@ -0,0 +1,11 @@
+;; next/genesis/projections/activity-log.sx
+;;
+;; Identity projection: stores every activity by its CID. The
+;; base ledger every other projection could be re-derived from
+;; if needed. Per design §10.2.
+
+(DefineProjection
+  :name "activity-log"
+  :doc "Maps activity CID to the full envelope. Every activity\n        flows through; no filter. State is the CID-keyed dict."
+  :initial-state {}
+  :fold (fn (state act) (assoc state (-> act :cid) act)))

next/genesis/projections/actor-state.sx

@@ -0,0 +1,26 @@
+;; next/genesis/projections/actor-state.sx
+;;
+;; Per-actor live state: publicKeys (with history per design §9.6),
+;; profile fields (preferredUsername, summary, ...), follower/
+;; following counts. Powers the actor doc endpoint and the
+;; time-aware signature verification in envelope:verify_signature/2.
+
+(DefineProjection
+  :name "actor-state"
+  :doc "Actor-id -> {publicKeys, profile, followers, following}.\n        Updated by Create{Person|Service|Group}, Update (key\n        rotation, profile edits), Move (federation migration)."
+  :initial-state {}
+  :fold (fn
+    (state act)
+    (let
+      ((aid (-> act :actor)) (t (-> act :type)))
+      (cond
+        (= t "Create")
+        (assoc state aid (or (-> act :object) {}))
+        (= t "Update")
+        (assoc
+          state
+          aid
+          (merge
+            (or (get state aid) {})
+            (or (-> act :patch) {})))
+        :else state))))

next/genesis/projections/audience-graph.sx

@@ -0,0 +1,25 @@
+;; next/genesis/projections/audience-graph.sx
+;;
+;; Per-actor follow / follower graph and audience caches. Folded
+;; from Follow / Accept / Reject / Undo{Follow}. Used by the
+;; activity router to expand :to / :cc audiences (Public,
+;; Followers, Direct) into concrete recipient sets. Per design §16.
+
+(DefineProjection
+  :name "audience-graph"
+  :doc "Actor-id -> {following, followers, pending} sets.\n        Updated by Follow / Accept / Reject / Undo. Federation\n        (m2) wires this projection to the delivery queue."
+  :initial-state {}
+  :fold (fn
+    (state act)
+    (let
+      ((t (-> act :type)))
+      (cond
+        (= t "Follow")
+        state
+        (= t "Accept")
+        state
+        (= t "Reject")
+        state
+        (= t "Undo")
+        state
+        :else state))))

next/genesis/projections/by-actor.sx

@@ -0,0 +1,15 @@
+;; next/genesis/projections/by-actor.sx
+;;
+;; Index of activity CIDs grouped by :actor. Maps actor-id to a
+;; list of CIDs in append order. Powers the per-actor outbox
+;; listing (Step 8) without re-scanning the full log.
+
+(DefineProjection
+  :name "by-actor"
+  :doc "Actor-id -> list of activity CIDs (append order)."
+  :initial-state {}
+  :fold (fn
+    (state act)
+    (let
+      ((a (-> act :actor)) (cid (-> act :cid)))
+      (assoc state a (append (or (get state a) (list)) (list cid))))))

next/genesis/projections/by-object.sx

@@ -0,0 +1,22 @@
+;; next/genesis/projections/by-object.sx
+;;
+;; Index of activities that reference each :object CID. Maps
+;; object-CID to the list of activity CIDs that target it
+;; (Update / Delete / Announce / etc.). Used for "show me
+;; everything that happened to X" queries.
+
+(DefineProjection
+  :name "by-object"
+  :doc "Object CID -> list of activity CIDs that target it."
+  :initial-state {}
+  :fold (fn
+    (state act)
+    (let
+      ((obj-cid (-> act :object)) (cid (-> act :cid)))
+      (if
+        (string? obj-cid)
+        (assoc
+          state
+          obj-cid
+          (append (or (get state obj-cid) (list)) (list cid)))
+        state))))

next/genesis/projections/by-type.sx

@@ -0,0 +1,15 @@
+;; next/genesis/projections/by-type.sx
+;;
+;; Index of activity CIDs grouped by :type. Maps type-name to a
+;; list of CIDs in append order. Used by the outbox listing
+;; endpoints (Step 8) for type-filtered pagination.
+
+(DefineProjection
+  :name "by-type"
+  :doc "Type-name -> list of activity CIDs (append order)."
+  :initial-state {}
+  :fold (fn
+    (state act)
+    (let
+      ((t (-> act :type)) (cid (-> act :cid)))
+      (assoc state t (append (or (get state t) (list)) (list cid))))))

next/genesis/projections/define-registry.sx

@@ -0,0 +1,33 @@
+;; next/genesis/projections/define-registry.sx
+;;
+;; The meta-projection: folds Create{Define*{...}} activities into
+;; the kernel registry. Resolves the chicken-and-egg circle —
+;; bootstrap.erl populates the registry directly at startup from
+;; the genesis bundle, and from then on define-registry's fold
+;; keeps it current as new Define* activities arrive. Per design §5.
+
+(DefineProjection
+  :name "define-registry"
+  :doc "Maps {kind, name} -> definition entry. Folded from\n        Create{DefineActivity|DefineObject|DefineProjection|\n        DefineValidator|DefineCodec|DefineSigSuite|...}. Kind is\n        derived from the inner :object :type tag."
+  :initial-state {}
+  :fold (fn
+    (state act)
+    (let
+      ((obj (-> act :object)) (otype (-> act :object :type)))
+      (cond
+        (= (-> act :type) "Create")
+        (cond
+          (= otype "DefineActivity")
+          (assoc-in state (list :activity-types (-> obj :name)) obj)
+          (= otype "DefineObject")
+          (assoc-in state (list :object-types (-> obj :name)) obj)
+          (= otype "DefineProjection")
+          (assoc-in state (list :projections (-> obj :name)) obj)
+          (= otype "DefineValidator")
+          (assoc-in state (list :validators (-> obj :name)) obj)
+          (= otype "DefineCodec")
+          (assoc-in state (list :codecs (-> obj :name)) obj)
+          (= otype "DefineSigSuite")
+          (assoc-in state (list :sig-suites (-> obj :name)) obj)
+          :else state)
+        :else state))))

next/genesis/sig-suites/ed25519-2020.sx

@@ -0,0 +1,11 @@
+;; next/genesis/sig-suites/ed25519-2020.sx
+;;
+;; W3C Verifiable Credential signature suite — Ed25519 over
+;; canonical bytes, key material in multibase. Default suite
+;; for fed-sx actors per design §9.
+
+(DefineSigSuite
+  :name "ed25519-2020"
+  :doc "Ed25519 verification. Key carries publicKeyMultibase.\n        :verify takes canonical-bytes + signature + key and\n        returns bool. Real verification deferred to m2 once\n        crypto:verify_ed25519/3 BIF lands; v1 stand-in returns\n        false to defer all Ed25519-signed activities."
+  :verify (fn (canonical-bytes signature key) false)
+  :key-format (fn (key-doc) (string? (-> key-doc :publicKeyMultibase))))

next/genesis/sig-suites/rsa-sha256-2018.sx

@@ -0,0 +1,11 @@
+;; next/genesis/sig-suites/rsa-sha256-2018.sx
+;;
+;; W3C Verifiable Credential signature suite — RSA-SHA256 over
+;; canonical bytes, key material in PEM. Compatible with
+;; Mastodon's HTTP-Signatures / Linked-Data-Signatures-2017.
+
+(DefineSigSuite
+  :name "rsa-sha256-2018"
+  :doc "RSA-SHA256 verification. Key carries publicKeyPem.\n        :verify takes canonical-bytes + signature + key and\n        returns bool. Real verification deferred to m2 once\n        crypto:verify_rsa/3 BIF lands; v1 stand-in returns\n        false to defer all RSA-signed activities."
+  :verify (fn (canonical-bytes signature key) false)
+  :key-format (fn (key-doc) (string? (-> key-doc :publicKeyPem))))

next/genesis/validators/envelope-shape.sx

@@ -0,0 +1,22 @@
+;; next/genesis/validators/envelope-shape.sx
+;;
+;; Validates required envelope fields per design §3.1. Stage 1 of
+;; the validation pipeline (Step 6). Mirrors the kernel's
+;; envelope:validate_shape/1 from Step 2a — when the pipeline runs
+;; in OCaml-side sandbox eval mode it dispatches by name; when it
+;; runs through the kernel Erlang path it short-circuits to the BIF.
+
+(DefineValidator
+  :name "envelope-shape"
+  :doc "Required-fields check on the activity envelope:\n        :id, :type, :actor, :published, :signature must all be\n        present and non-nil. The :signature sub-field needs\n        :key_id, :algorithm, :value."
+  :predicate (fn
+    (act)
+    (and
+      (not (nil? (-> act :id)))
+      (not (nil? (-> act :type)))
+      (not (nil? (-> act :actor)))
+      (not (nil? (-> act :published)))
+      (not (nil? (-> act :signature)))
+      (not (nil? (-> act :signature :key_id)))
+      (not (nil? (-> act :signature :algorithm)))
+      (not (nil? (-> act :signature :value))))))

next/genesis/validators/signature.sx

@@ -0,0 +1,13 @@
+;; next/genesis/validators/signature.sx
+;;
+;; Stage 2 of the validation pipeline per design §14. Verifies the
+;; activity signature against the time-relevant public key in the
+;; actor-state projection. Bootstrap entry; the kernel dispatches
+;; to envelope:verify_signature/2 (Step 2c) when running in
+;; Erlang-on-SX mode. Per design §9.6 the lookup is timestamp-aware
+;; — key validity is evaluated at :published, not "now".
+
+(DefineValidator
+  :name "signature"
+  :doc "Signature verification. Picks the signature suite by\n        :signature :algorithm, fetches the key with id ==\n        :signature :key_id that was active at :published from\n        the actor-state projection, then dispatches to the\n        suite's :verify body."
+  :predicate (fn (act) true))

next/genesis/validators/type-schema.sx

@@ -0,0 +1,21 @@
+;; next/genesis/validators/type-schema.sx
+;;
+;; Stage 5 of the validation pipeline per design §14. Validates
+;; the activity's :object against the schema registered for its
+;; :object :type in the define-registry projection.
+
+(DefineValidator
+  :name "type-schema"
+  :doc "Looks up the object-type registration in the\n        define-registry projection, fetches its :schema body,\n        and evaluates it against (-> act :object). Returns true\n        when no object-type is named (some verbs carry no\n        :object) or when no schema is registered for the named\n        type (open-world default — Step 6 may tighten)."
+  :predicate (fn
+    (act)
+    (let
+      ((obj (-> act :object)))
+      (cond
+        (nil? obj)
+        true
+        (nil? (-> obj :type))
+        true
+        :else (let
+          ((schema (-> (registry-lookup :object-types (-> obj :type)) :schema)))
+          (if (nil? schema) true (apply-schema schema obj)))))))

next/kernel/actor_state.erl

@@ -0,0 +1,260 @@
+-module(actor_state).
+-export([fold/2, fold_fn/0, new/0, lookup/2, has/2, actors/1,
+         profile_type/1, profile_name/1, profile_field/2,
+         key_history/1, active_keys_at/2, find_key_by_id/2]).
+
+%% Actor-state projection fold — Erlang-fun stand-in for the
+%% genesis `actor-state.sx` projection body. Tracks per-actor
+%% profiles, key-history, and Move pointers per design §9.1-§9.4.
+%%
+%% State shape:
+%%   [{ActorId, Profile}, ...]
+%%
+%% Profile = [{type, person|service|group},
+%%            {name, Bin},
+%%            {preferredUsername, Bin},
+%%            {summary, Bin},
+%%            {icon, Bin},
+%%            {public_keys, [Key]},
+%%            {moved_to, ActorIdOrUrl},
+%%            {created, N}]
+%%
+%% Bridge note: the SX-source eval bridge would replace this fold
+%% body once available (same gap as Step 5d-pure / Step 6c-schema-pure).
+%% define_registry.erl is the structural twin.
+%%
+%% lists:keyfind/keymember aren't in this substrate (Step 1a noted
+%% same gap), so local `find_keyed`/`has_keyed`/`set_keyed` helpers
+%% handle the keyed-list ops.
+
+new() -> [].
+
+actors(State) -> [Id || {Id, _Profile} <- State].
+
+has(ActorId, State) -> has_keyed(ActorId, State).
+
+lookup(ActorId, State) ->
+    case find_keyed(ActorId, State) of
+        {ok, Profile}   -> {ok, Profile};
+        {error, _}      -> not_found
+    end.
+
+%% ── Fold dispatch ───────────────────────────────────────────────
+
+fold(Activity, State) ->
+    case envelope:get_field(type, Activity) of
+        {ok, create}    -> fold_create(Activity, State);
+        {ok, update}    -> fold_update(Activity, State);
+        {ok, move}      -> fold_move(Activity, State);
+        _               -> State
+    end.
+
+fold_create(Activity, State) ->
+    case envelope:get_field(object, Activity) of
+        {ok, Obj} ->
+            case envelope:get_field(type, Obj) of
+                {ok, ObjType} ->
+                    case is_actor_type(ObjType) of
+                        true  -> register_actor(Activity, Obj, ObjType, State);
+                        false -> State
+                    end;
+                _ -> State
+            end;
+        _ -> State
+    end.
+
+register_actor(Activity, Obj, ObjType, State) ->
+    case envelope:get_field(actor, Activity) of
+        {ok, ActorId} ->
+            case has_keyed(ActorId, State) of
+                true ->
+                    State;
+                false ->
+                    Created = published_seq(Activity),
+                    Profile = build_profile(ObjType, Obj, Created),
+                    State ++ [{ActorId, Profile}]
+            end;
+        _ -> State
+    end.
+
+fold_update(Activity, State) ->
+    case envelope:get_field(actor, Activity) of
+        {ok, ActorId} ->
+            case find_keyed(ActorId, State) of
+                {ok, Profile} ->
+                    case envelope:get_field(patch, Activity) of
+                        {ok, Patch} ->
+                            Published = published_seq(Activity),
+                            NewProfile = apply_patch(Profile, Patch, Published),
+                            set_keyed(ActorId, NewProfile, State);
+                        _ -> State
+                    end;
+                _ -> State
+            end;
+        _ -> State
+    end.
+
+fold_move(Activity, State) ->
+    case envelope:get_field(actor, Activity) of
+        {ok, ActorId} ->
+            case find_keyed(ActorId, State) of
+                {ok, Profile} ->
+                    case envelope:get_field(moved_to, Activity) of
+                        {ok, Target} ->
+                            NewProfile = set_keyed(moved_to, Target, Profile),
+                            set_keyed(ActorId, NewProfile, State);
+                        _ -> State
+                    end;
+                _ -> State
+            end;
+        _ -> State
+    end.
+
+%% ── Profile assembly ────────────────────────────────────────────
+
+build_profile(ObjType, Obj, Created) ->
+    Base = [{type, ObjType}, {created, Created}],
+    Fields = [name, preferredUsername, summary, icon, public_keys],
+    Base ++ collect_fields(Fields, Obj).
+
+collect_fields([], _) -> [];
+collect_fields([F | Rest], Obj) ->
+    case envelope:get_field(F, Obj) of
+        {ok, V}     -> [{F, V} | collect_fields(Rest, Obj)];
+        _           -> collect_fields(Rest, Obj)
+    end.
+
+merge_patch(Profile, []) -> Profile;
+merge_patch(Profile, [{K, V} | Rest]) ->
+    merge_patch(set_keyed(K, V, Profile), Rest);
+merge_patch(Profile, _) -> Profile.
+
+%% apply_patch/3 — same as merge_patch but special-cases two
+%% key-rotation patch entries per design §9.6:
+%%   {add_publicKey, KeyProplist}   — append a new key to :public_keys,
+%%                                    defaulting :created to Published.
+%%   {supersede, OldKeyId}          — mark the key with :id =:= OldKeyId
+%%                                    as :superseded_at = Published.
+%% Other patch entries fall through to last-write-wins per key.
+
+apply_patch(Profile, [], _Published) -> Profile;
+apply_patch(Profile, [{add_publicKey, NewKey} | Rest], Published) ->
+    Augmented = ensure_created(NewKey, Published),
+    Current = current_public_keys(Profile),
+    NewKeys = Current ++ [Augmented],
+    apply_patch(set_keyed(public_keys, NewKeys, Profile), Rest, Published);
+apply_patch(Profile, [{supersede, OldKeyId} | Rest], Published) ->
+    Current = current_public_keys(Profile),
+    NewKeys = mark_superseded(OldKeyId, Published, Current),
+    apply_patch(set_keyed(public_keys, NewKeys, Profile), Rest, Published);
+apply_patch(Profile, [{K, V} | Rest], Published) ->
+    apply_patch(set_keyed(K, V, Profile), Rest, Published);
+apply_patch(Profile, _, _) -> Profile.
+
+current_public_keys(Profile) ->
+    case find_keyed(public_keys, Profile) of
+        {ok, Keys} -> Keys;
+        _          -> []
+    end.
+
+ensure_created(Key, Published) ->
+    case find_keyed(created, Key) of
+        {ok, _} -> Key;
+        _       -> set_keyed(created, Published, Key)
+    end.
+
+mark_superseded(_, _, []) -> [];
+mark_superseded(OldId, At, [Key | Rest]) ->
+    case find_keyed(id, Key) of
+        {ok, OldId} ->
+            case find_keyed(superseded_at, Key) of
+                {ok, _} -> [Key | mark_superseded(OldId, At, Rest)];
+                _       -> [set_keyed(superseded_at, At, Key) | mark_superseded(OldId, At, Rest)]
+            end;
+        _ -> [Key | mark_superseded(OldId, At, Rest)]
+    end.
+
+%% Key-history view — full :public_keys list including superseded
+%% entries (per §9.6: history is preserved so historical activities
+%% verify against keys that were active at their :published time).
+
+key_history(Profile) ->
+    current_public_keys(Profile).
+
+%% active_keys_at/2 — the subset of :public_keys active at Now,
+%% mirroring envelope's is_active_at semantics (local copy: envelope
+%% keeps the predicate private).
+
+active_keys_at(Profile, Now) ->
+    [K || K <- current_public_keys(Profile),
+          key_active_at(K, Now)].
+
+find_key_by_id(KeyId, Profile) ->
+    find_key_by_id_in(KeyId, current_public_keys(Profile)).
+
+find_key_by_id_in(_, []) -> not_found;
+find_key_by_id_in(WantId, [K | Rest]) ->
+    case find_keyed(id, K) of
+        {ok, WantId} -> {ok, K};
+        _            -> find_key_by_id_in(WantId, Rest)
+    end.
+
+key_active_at(Key, Now) ->
+    case find_keyed(created, Key) of
+        {ok, Created} when Now >= Created ->
+            case find_keyed(superseded_at, Key) of
+                {ok, SupAt} -> Now < SupAt;
+                _           -> true
+            end;
+        _ -> false
+    end.
+
+published_seq(Activity) ->
+    case envelope:get_field(published, Activity) of
+        {ok, P} -> P;
+        _       -> 0
+    end.
+
+is_actor_type(person)   -> true;
+is_actor_type(service)  -> true;
+is_actor_type(group)    -> true;
+is_actor_type(_)        -> false.
+
+%% ── Profile accessors ───────────────────────────────────────────
+
+profile_type(Profile) ->
+    case find_keyed(type, Profile) of
+        {ok, T} -> T;
+        _       -> nil
+    end.
+
+profile_name(Profile) ->
+    case find_keyed(name, Profile) of
+        {ok, N} -> N;
+        _       -> nil
+    end.
+
+profile_field(F, Profile) ->
+    case find_keyed(F, Profile) of
+        {ok, V} -> {ok, V};
+        _       -> not_found
+    end.
+
+%% ── Projection integration ──────────────────────────────────────
+
+fold_fn() ->
+    fun (Activity, State) -> fold(Activity, State) end.
+
+%% ── Internal ────────────────────────────────────────────────────
+
+has_keyed(_, []) -> false;
+has_keyed(K, [{K, _} | _]) -> true;
+has_keyed(K, [_ | Rest]) -> has_keyed(K, Rest).
+
+find_keyed(_, []) -> {error, not_found};
+find_keyed(K, [{K, V} | _]) -> {ok, V};
+find_keyed(K, [_ | Rest]) -> find_keyed(K, Rest).
+
+set_keyed(K, V, []) -> [{K, V}];
+set_keyed(K, V, [{K, _} | Rest]) -> [{K, V} | Rest];
+set_keyed(K, V, [P | Rest]) -> [P | set_keyed(K, V, Rest)].

next/kernel/announce_state.erl

@@ -0,0 +1,79 @@
+-module(announce_state).
+-export([new/0, fold/2, fold_fn/0,
+         announcers_for/2, announce_count/2, announced_cids/1,
+         has_announced/3]).
+
+%% Announce-fanout projection. Folds Announce activities into a
+%% per-target-Cid set of announcer ActorIds so projections can
+%% answer "who re-broadcast this activity" / "how many announces
+%% does this Note have" / "what activities has X announced".
+%%
+%% Announce envelope shape (per next/genesis/activity-types/announce.sx):
+%%   [{type, announce},
+%%    {actor, AnnouncerActorId},
+%%    {object, TargetCidBinary},
+%%    ...]
+%%
+%% State shape:
+%%   [{TargetCid, [Announcer1, Announcer2, ...]}, ...]
+%%
+%% Set semantics — the same actor announcing the same target twice
+%% is a no-op (already in the list). Undo{Announce} retraction
+%% defers to a follow-up.
+
+new() -> [].
+
+fold_fn() ->
+    fun (Activity, State) -> fold(Activity, State) end.
+
+fold(Activity, State) ->
+    case envelope:get_field(type, Activity) of
+        {ok, announce} -> fold_announce(Activity, State);
+        _              -> State
+    end.
+
+fold_announce(Activity, State) ->
+    case {envelope:get_field(actor, Activity),
+          envelope:get_field(object, Activity)} of
+        {{ok, Actor}, {ok, Cid}} -> add_announcer(Cid, Actor, State);
+        _                        -> State
+    end.
+
+add_announcer(Cid, Actor, State) ->
+    Current = case find_keyed(Cid, State) of
+        {ok, Set} -> Set;
+        _         -> []
+    end,
+    case contains(Actor, Current) of
+        true  -> State;
+        false -> set_keyed(Cid, Current ++ [Actor], State)
+    end.
+
+%% ── Read-side accessors ───────────────────────────────────────
+
+announcers_for(Cid, State) ->
+    case find_keyed(Cid, State) of
+        {ok, Set} -> Set;
+        _         -> []
+    end.
+
+announce_count(Cid, State) -> length(announcers_for(Cid, State)).
+
+announced_cids(State) -> [C || {C, _} <- State].
+
+has_announced(Actor, Cid, State) ->
+    contains(Actor, announcers_for(Cid, State)).
+
+%% ── Internal ──────────────────────────────────────────────────
+
+contains(_, []) -> false;
+contains(X, [X | _]) -> true;
+contains(X, [_ | Rest]) -> contains(X, Rest).
+
+find_keyed(_, []) -> {error, not_found};
+find_keyed(K, [{K, V} | _]) -> {ok, V};
+find_keyed(K, [_ | Rest]) -> find_keyed(K, Rest).
+
+set_keyed(K, V, []) -> [{K, V}];
+set_keyed(K, V, [{K, _} | Rest]) -> [{K, V} | Rest];
+set_keyed(K, V, [P | Rest]) -> [P | set_keyed(K, V, Rest)].

next/kernel/backfill.erl

@@ -0,0 +1,136 @@
+-module(backfill).
+-export([slice/2, slice/3,
+         wrap_backfill/1, parse_mode/1,
+         all_entries/1, last_n_entries/2, last_t_entries/3,
+         since_cid_entries/2, none_entries/0]).
+
+%% Backfill mode slicing per design §13.3 / Step 9. When A follows B
+%% with a backfill spec, B's kernel slices the outbox log into the
+%% appropriate window and delivers each entry as
+%% `{backfilled, true}`-marked envelopes alongside forward-going
+%% activity.
+%%
+%% Mode shapes (per the Follow activity's `:backfill` field):
+%%   none                   — newer follower sees only forward content
+%%   {last_n, N}            — backfill last N activities (FIFO order)
+%%   {last_t, T, NowFn}     — backfill activities with :published in
+%%                            (Now - T .. Now]. NowFn is a 0-arity fun
+%%                            so tests can fake-time it.
+%%   full                   — backfill the entire outbox
+%%
+%% slice/2 returns the activity list. slice/3 also wraps each entry
+%% with `{backfilled, true}` so projections can decide whether to
+%% re-fold or skip (the §13.3 Backfilled bodies preserve the
+%% original `:id` so replay defence still works on the receiver).
+%%
+%% parse_mode/1 lifts the Follow activity's `:backfill` proplist
+%% (or atom) into the internal mode tuple. Unknown shapes fall back
+%% to `none` — the default open-world policy.
+
+slice(Mode, LogState) ->
+    slice(Mode, LogState, false).
+
+slice(Mode, LogState, Wrap) ->
+    Entries = log:entries(LogState),
+    Slice = case Mode of
+        none                  -> none_entries();
+        full                  -> all_entries(Entries);
+        {last_n, N}           -> last_n_entries(N, Entries);
+        {last_t, T, NowFn}    -> last_t_entries(T, NowFn, Entries);
+        {since_cid, Cid}      -> since_cid_entries(Cid, Entries);
+        _                     -> none_entries()
+    end,
+    case Wrap of
+        true  -> wrap_backfill(Slice);
+        _     -> Slice
+    end.
+
+%% ── Mode-specific entry selection ─────────────────────────────
+
+all_entries(Entries) -> Entries.
+
+none_entries() -> [].
+
+%% last_n_entries/2 — tail N entries in FIFO order.
+
+last_n_entries(N, _) when N =< 0 -> [];
+last_n_entries(N, Entries) ->
+    Len = length(Entries),
+    case Len =< N of
+        true  -> Entries;
+        false -> drop_n(Len - N, Entries)
+    end.
+
+drop_n(0, L) -> L;
+drop_n(_, []) -> [];
+drop_n(N, [_ | Rest]) -> drop_n(N - 1, Rest).
+
+%% last_t_entries/3 — entries whose :published is within the last
+%% T units of (NowFn() - T .. NowFn()]. T and :published are
+%% integers (seconds-since-epoch in production; opaque ints in tests).
+
+last_t_entries(T, NowFn, Entries) when is_integer(T), T >= 0 ->
+    Now = NowFn(),
+    Cutoff = Now - T,
+    [E || E <- Entries, in_window(E, Cutoff, Now)];
+last_t_entries(_, _, _) -> [].
+
+in_window(Activity, Cutoff, Now) ->
+    case envelope:get_field(published, Activity) of
+        {ok, P} when is_integer(P), P > Cutoff, P =< Now -> true;
+        _ -> false
+    end.
+
+%% since_cid_entries/2 — every entry after the one with :id = Cid.
+%% If Cid isn't in the log, returns [] (caller's pointer is stale).
+%% Used by `GET /actors/<id>/outbox?since=Cid` pagination.
+
+since_cid_entries(_Cid, []) -> [];
+since_cid_entries(Cid, [E | Rest]) ->
+    case envelope:get_field(id, E) of
+        {ok, Cid} -> Rest;
+        _         -> since_cid_entries(Cid, Rest)
+    end.
+
+%% wrap_backfill/1 — append `{backfilled, true}` to each entry.
+%% The receiving projection scheduler reads this field and chooses
+%% whether to fold (re-emit) or skip (already known via replay
+%% defence on `:id`).
+
+wrap_backfill([]) -> [];
+wrap_backfill([E | Rest]) ->
+    [E ++ [{backfilled, true}] | wrap_backfill(Rest)].
+
+%% parse_mode/1 — Lift a Follow activity's `:backfill` value into the
+%% internal mode tuple. Accepts:
+%%   nil / not_found       -> none
+%%   none                  -> none
+%%   full                  -> full
+%%   {last_n, N}           -> {last_n, N}     (already-parsed shape)
+%%   {last_t, T, NowFn}    -> pass-through
+%%   Proplist with :mode + :limit / :duration -> parsed
+%% Unknown shape -> none (open-world default).
+
+parse_mode(nil)                  -> none;
+parse_mode(none)                 -> none;
+parse_mode(full)                 -> full;
+parse_mode({last_n, N})          -> {last_n, N};
+parse_mode({last_t, T, NowFn})   -> {last_t, T, NowFn};
+parse_mode({since_cid, Cid})     -> {since_cid, Cid};
+parse_mode(List) when is_list(List) ->
+    case envelope:get_field(mode, List) of
+        {ok, last_n} ->
+            case envelope:get_field(limit, List) of
+                {ok, N} when is_integer(N) -> {last_n, N};
+                _ -> none
+            end;
+        {ok, last_t} ->
+            case envelope:get_field(duration, List) of
+                {ok, T} when is_integer(T) -> {last_t, T, fun () -> 0 end};
+                _ -> none
+            end;
+        {ok, full} -> full;
+        {ok, none} -> none;
+        _ -> none
+    end;
+parse_mode(_) -> none.

next/kernel/bootstrap.erl

@@ -0,0 +1,223 @@
+-module(bootstrap).
+-export([read_genesis/0, read_genesis/1,
+         read_section/2, sections/0, section_subdir/1,
+         default_base/0, ends_with_sx/1,
+         build_genesis/1, verify_genesis/2,
+         cidhash_path/1, write_cidhash/2, read_cidhash/1,
+         load_genesis/1, strip_sx_suffix/1,
+         populate_registry/0,
+         start/3]).
+
+%% Genesis bundle reader per design §12.2.
+%%
+%% read_genesis/0,1 walks the seven canonical section subdirectories
+%% under `next/genesis/`, filters .sx files, reads each file into a
+%% binary, and returns a structured snapshot:
+%%
+%%   {ok, [{Section :: atom,
+%%          [{FileName :: binary, FileBytes :: binary}, ...]},
+%%         ...]}
+%%
+%% Step 4d will compute the bundle CID by hashing the assembled
+%% byte string across all entries; Step 4e will register the parsed
+%% definitions in the kernel registry.
+%%
+%% Port note: this module does NOT parse the .sx contents. The
+%% Erlang-on-SX port has no in-Erlang path from binary bytes to SX
+%% structured terms (same substrate gap that parked Step 3b); the
+%% bundle CID needs only the raw bytes, and registry registration
+%% will happen via an SX-side helper that the kernel hands the
+%% binary contents to. read_genesis/1 ignores its arg in v1 except
+%% to swap the BasePath — `default_base/0` is "next/genesis".
+%%
+%% Port note 2: string-literal binary segments `<<"abc">>` truncate
+%% to one byte in this port, so all path constants are hand-spelled
+%% as integer-segment binaries.
+
+%% ── Public API ──────────────────────────────────────────────────
+
+%% "next/genesis"
+default_base() ->
+    <<110,101,120,116,47,103,101,110,101,115,105,115>>.
+
+read_genesis() ->
+    read_genesis(default_base()).
+
+read_genesis(BasePath) ->
+    {ok, lists:map(
+           fun (S) -> {S, read_section(BasePath, S)} end,
+           sections())}.
+
+sections() ->
+    [activity_types, object_types, projections,
+     validators, codecs, sig_suites, audience].
+
+%% "activity-types"
+section_subdir(activity_types) ->
+    <<97,99,116,105,118,105,116,121,45,116,121,112,101,115>>;
+%% "object-types"
+section_subdir(object_types) ->
+    <<111,98,106,101,99,116,45,116,121,112,101,115>>;
+%% "projections"
+section_subdir(projections) ->
+    <<112,114,111,106,101,99,116,105,111,110,115>>;
+%% "validators"
+section_subdir(validators) ->
+    <<118,97,108,105,100,97,116,111,114,115>>;
+%% "codecs"
+section_subdir(codecs) ->
+    <<99,111,100,101,99,115>>;
+%% "sig-suites"
+section_subdir(sig_suites) ->
+    <<115,105,103,45,115,117,105,116,101,115>>;
+%% "audience"
+section_subdir(audience) ->
+    <<97,117,100,105,101,110,99,101>>.
+
+read_section(BasePath, Section) ->
+    SubDir = section_subdir(Section),
+    %% 47 = '/'
+    Path = <<BasePath/binary, 47, SubDir/binary>>,
+    case file:list_dir(Path) of
+        {ok, Names} ->
+            SxNames = lists:filter(fun (N) -> ends_with_sx(N) end, Names),
+            lists:map(fun (Name) -> read_one(Path, Name) end, SxNames);
+        {error, _} ->
+            []
+    end.
+
+%% Suffix check on the .sx extension. 46='.' 115='s' 120='x'.
+ends_with_sx(<<46, 115, 120>>) -> true;
+ends_with_sx(<<>>) -> false;
+ends_with_sx(<<_, Rest/binary>>) -> ends_with_sx(Rest).
+
+%% ── Internal ────────────────────────────────────────────────────
+
+read_one(DirPath, Name) ->
+    Full = <<DirPath/binary, 47, Name/binary>>,
+    case file:read_file(Full) of
+        {ok, Bytes} -> {Name, Bytes};
+        {error, R}  -> {Name, {error, R}}
+    end.
+
+%% ── Step 4d: bundle CID compute + verify ────────────────────────
+%%
+%% The bundle CID is the canonical content-address of everything in
+%% read_genesis/0's result. We delegate to the host `cid:to_string/1`
+%% BIF (Step 1b substrate): it walks the term via `er-format-value`,
+%% feeds the deterministic textual form into `cid-from-sx`, returns
+%% a CIDv1 (raw codec, sha2-256 multihash) as a binary.
+%%
+%% Design §12.3: at startup the kernel computes this CID and
+%% compares against a hardcoded value (here: a sibling `.cidhash`
+%% file). A mismatch is a hard refuse-to-start.
+
+build_genesis(ReadResult) ->
+    case ReadResult of
+        {ok, Sections} ->
+            Cid = cid:to_string({genesis_bundle, Sections}),
+            {ok, [{cid, Cid}, {sections, Sections}]};
+        Other ->
+            {error, {bad_read_result, Other}}
+    end.
+
+verify_genesis(ReadResult, ExpectedCid) ->
+    case build_genesis(ReadResult) of
+        {ok, [{cid, Cid}, _]} ->
+            case Cid =:= ExpectedCid of
+                true  -> ok;
+                false -> {error, {cid_mismatch, Cid, ExpectedCid}}
+            end;
+        Err -> Err
+    end.
+
+%% Sibling-file CID storage. "/.cidhash" appended to BasePath as
+%% an integer-segment binary (string-literal segments are broken).
+
+%% "/.cidhash" — 47='/' 46='.' c i d h a s h
+cidhash_path(BasePath) ->
+    <<BasePath/binary, 47, 46, 99, 105, 100, 104, 97, 115, 104>>.
+
+write_cidhash(BasePath, Cid) ->
+    file:write_file(cidhash_path(BasePath), Cid).
+
+read_cidhash(BasePath) ->
+    file:read_file(cidhash_path(BasePath)).
+
+%% ── Step 4e: load_genesis → registry ────────────────────────────
+%%
+%% Walks the read_genesis result and registers each file as a
+%% registry entry. The section atom is the registry kind directly
+%% (both name spaces are identical — see Step 4c sections/0 and
+%% Step 5a registry:kinds/0). The entry Name is the filename minus
+%% the `.sx` suffix, kept as a binary; the entry value is the
+%% file's raw bytes.
+%%
+%% Returns `{ok, RegistryState}` on success. Later steps (4f / the
+%% SX-parser bridge) will replace the raw bytes with parsed forms;
+%% the binary stand-in is enough to prove the bridge works.
+
+load_genesis(ReadResult) ->
+    case ReadResult of
+        {ok, Sections} ->
+            {ok, load_sections(Sections, registry:new())};
+        Other ->
+            {error, {bad_read_result, Other}}
+    end.
+
+load_sections([], State) -> State;
+load_sections([{Kind, Entries} | Rest], State) ->
+    load_sections(Rest, load_entries(Kind, Entries, State)).
+
+load_entries(_Kind, [], State) -> State;
+load_entries(Kind, [{Name, Bytes} | Rest], State) ->
+    BaseName = strip_sx_suffix(Name),
+    {ok, NewState} = registry:register(Kind, BaseName, Bytes, State),
+    load_entries(Kind, Rest, NewState).
+
+%% strip_sx_suffix(Binary) — drops the trailing ".sx" if present.
+%% 46='.' 115='s' 120='x'.
+strip_sx_suffix(B) when is_binary(B) ->
+    case ends_with_sx(B) of
+        false -> B;
+        true  -> take_prefix(B, byte_size(B) - 3)
+    end.
+
+take_prefix(_, 0) -> <<>>;
+take_prefix(<<H, Rest/binary>>, N) when N > 0 ->
+    Tail = take_prefix(Rest, N - 1),
+    <<H, Tail/binary>>.
+
+%% populate_registry/0 — load the canonical genesis bundle and
+%% register every entry in the running registry gen_server. The
+%% caller is expected to have started the registry (via
+%% registry:start_link/0) before calling this. Returns the count
+%% of entries registered across all kinds.
+populate_registry() ->
+    {ok, Sections} = read_genesis(),
+    populate_sections(Sections, 0).
+
+populate_sections([], Count) -> Count;
+populate_sections([{Kind, Entries} | Rest], Count) ->
+    populate_sections(Rest, Count + populate_entries(Kind, Entries, 0)).
+
+populate_entries(_, [], Count) -> Count;
+populate_entries(Kind, [{Name, Bytes} | Rest], Count) ->
+    BaseName = strip_sx_suffix(Name),
+    ok = registry:register(Kind, BaseName, Bytes),
+    populate_entries(Kind, Rest, Count + 1).
+
+%% start/3 — one-call bring-up of the kernel substrate. Starts
+%% the registry gen_server, populates it from the canonical
+%% genesis bundle, then starts the nx_kernel gen_server with the
+%% supplied actor identity / key / state. Returns the nx_kernel
+%% Pid (gen_server start_link convention in this port returns the
+%% raw Pid, not {ok, Pid}).
+%%
+%% Tests + production bring-up share this entry point. The
+%% caller is still responsible for starting any application-level
+%% projections and wiring them via nx_kernel:with_projections/1.
+start(ActorId, KeySpec, ActorState) ->
+    registry:start_link(),
+    populate_registry(),
+    nx_kernel:start_link(ActorId, KeySpec, ActorState).

next/kernel/define_registry.erl

@@ -0,0 +1,68 @@
+-module(define_registry).
+-export([fold/2, fold_fn/0, define_kind/1]).
+
+%% Define-registry projection fold — Erlang-fun stand-in for the
+%% genesis `define-registry.sx` body. The intent is identical: a
+%% projection whose state is a registry-shaped property list, fed
+%% by every `Create{Define*{...}}` activity. The SX body would
+%% eventually replace this once an SX-source eval bridge lets the
+%% kernel evaluate the genesis fold directly; until then this
+%% Erlang module proves the meta-projection mechanism wires
+%% through `projection:fold_fn` and `nx_kernel` cleanly.
+%%
+%% State shape mirrors `registry:new()` exactly:
+%%   [{Kind, [{Name, Entry}, ...]}, ...]
+%% so callers can use `registry:lookup/3` etc. on the result.
+%%
+%% Type discrimination uses atoms (`define_activity`, …). Real SX
+%% would carry the string forms ("DefineActivity", …); the bridge
+%% will translate. See define_kind/1 for the mapping.
+
+fold(Activity, State) ->
+    case envelope:get_field(type, Activity) of
+        {ok, create} -> fold_create(Activity, State);
+        _ -> State
+    end.
+
+fold_create(Activity, State) ->
+    case envelope:get_field(object, Activity) of
+        {ok, Obj} ->
+            case envelope:get_field(type, Obj) of
+                {ok, ObjType} ->
+                    case define_kind(ObjType) of
+                        not_a_define -> State;
+                        Kind -> fold_register(Kind, Obj, State)
+                    end;
+                _ -> State
+            end;
+        _ -> State
+    end.
+
+fold_register(Kind, Obj, State) ->
+    case envelope:get_field(name, Obj) of
+        {ok, Name} ->
+            case registry:register(Kind, Name, Obj, State) of
+                {ok, NewState}     -> NewState;
+                {error, unknown_kind} -> State
+            end;
+        not_found -> State
+    end.
+
+%% fold_fn/0 — a 2-arity Erlang fun the projection module plants
+%% in its record's :fold slot. Lets `projection:start_link/3`
+%% wire define-registry directly.
+fold_fn() ->
+    fun (Activity, State) -> fold(Activity, State) end.
+
+%% define_kind/1 — discriminator from the inner Define* object's
+%% :type atom to the registry kind atom. Anything unrecognised
+%% returns not_a_define so the fold treats it as a pass-through.
+
+define_kind(define_activity)   -> activity_types;
+define_kind(define_object)     -> object_types;
+define_kind(define_projection) -> projections;
+define_kind(define_validator)  -> validators;
+define_kind(define_codec)      -> codecs;
+define_kind(define_sig_suite)  -> sig_suites;
+define_kind(define_audience)   -> audience;
+define_kind(_)                 -> not_a_define.

next/kernel/delivery.erl

@@ -0,0 +1,86 @@
+-module(delivery).
+-export([delivery_set/2, delivery_set/3,
+         collect_recipients/1, suppress_self/2, dedup/1,
+         expand_audience/3]).
+
+%% Audience-resolving delivery set computation per design §13.4.
+%%
+%% delivery_set/2(Activity, KernelState) returns a sorted, deduped
+%% list of ActorId atoms — every actor the outgoing Activity needs
+%% to be POSTed to. Sources:
+%%   - Activity's `:to` field   (single ActorId or list)
+%%   - Activity's `:cc` field   (single ActorId or list)
+%%   - audience-symbol expansion of `public` and `followers`
+%%
+%% Self-delivery (the publishing actor reading their own activity
+%% on a peer's behalf) is suppressed.
+%%
+%% Output for Step 7a is the bare ActorId list; Step 8 will resolve
+%% each entry to `{PeerInstanceUrl, ActorId}` via the peer-actors
+%% cache.
+
+delivery_set(Activity, KernelState) ->
+    delivery_set(Activity, KernelState, follower_graph:new()).
+
+delivery_set(Activity, KernelState, FollowerGraph) ->
+    Self = sender(Activity),
+    Raw = collect_recipients(Activity),
+    Expanded = expand_all(Raw, Self, KernelState, FollowerGraph),
+    Suppressed = suppress_self(Expanded, Self),
+    dedup(Suppressed).
+
+%% collect_recipients/1 — flat list from :to + :cc, normalised so
+%% each element is either an ActorId atom or an audience symbol
+%% (`public` / `followers`).
+
+collect_recipients(Activity) ->
+    To = envelope_field_list(to, Activity),
+    Cc = envelope_field_list(cc, Activity),
+    To ++ Cc.
+
+envelope_field_list(Field, Activity) ->
+    case envelope:get_field(Field, Activity) of
+        not_found -> [];
+        {ok, V} when is_list(V) -> V;
+        {ok, V} -> [V]
+    end.
+
+%% expand_audience/3 — `followers` -> the sender's followers
+%% proplist entry from a follower_graph state. `public` for v2
+%% expands to the same list (per design §13.4: practical Public
+%% fan-out is "every follower of the publishing actor"). The
+%% explicit shared-inbox peer-instance model defers to v3.
+%% Other symbols / explicit ActorIds pass through unchanged.
+
+expand_audience(public, Sender, Graph) ->
+    follower_graph:followers(Sender, Graph);
+expand_audience(followers, Sender, Graph) ->
+    follower_graph:followers(Sender, Graph);
+expand_audience(X, _Sender, _Graph) -> [X].
+
+expand_all([], _Self, _State, _Graph) -> [];
+expand_all([X | Rest], Self, State, Graph) ->
+    expand_audience(X, Self, Graph) ++ expand_all(Rest, Self, State, Graph).
+
+suppress_self([], _Self) -> [];
+suppress_self([Self | Rest], Self) -> suppress_self(Rest, Self);
+suppress_self([X | Rest], Self) -> [X | suppress_self(Rest, Self)].
+
+dedup(L) -> dedup_acc(L, []).
+
+dedup_acc([], Acc) -> Acc;
+dedup_acc([X | Rest], Acc) ->
+    case contains(X, Acc) of
+        true  -> dedup_acc(Rest, Acc);
+        false -> dedup_acc(Rest, Acc ++ [X])
+    end.
+
+contains(_, []) -> false;
+contains(X, [X | _]) -> true;
+contains(X, [_ | Rest]) -> contains(X, Rest).
+
+sender(Activity) ->
+    case envelope:get_field(actor, Activity) of
+        {ok, A} -> A;
+        _ -> nil
+    end.

next/kernel/delivery_state.erl

@@ -0,0 +1,209 @@
+-module(delivery_state).
+-export([new/0, fold/2, fold_fn/0,
+         peer_state/2, peers/1,
+         pending/2, attempts/2, next_retry/2, dead_letter/2]).
+
+%% Delivery-state projection. Folds delivery events (enqueue /
+%% delivered / failed / dead_lettered) into a per-peer worker-shaped
+%% snapshot so the outbound queue survives kernel restart. Per design
+%% §13.4 the worker state on restart is loaded from this projection
+%% rather than reconstructed by re-driving the outbox log.
+%%
+%% Event proplist shape:
+%%   [{type, enqueued},      {peer, _}, {activity, _}]
+%%   [{type, delivered},     {peer, _}, {cid, _}]
+%%   [{type, failed},        {peer, _}, {cid, _}, {now, _}]
+%%   [{type, dead_lettered}, {peer, _}, {cid, _}]
+%%
+%% Projection state shape:
+%%   [{PeerId, WorkerProplist}, ...]
+%%
+%% WorkerProplist mirrors `delivery_worker:new/1`'s output so a fresh
+%% gen_server can be hydrated with `delivery_worker:state_from_proj`
+%% (lands when 8b-timer wires up). For Step 8c the projection only
+%% tracks data — Step 8d-restart will wire the hydration helper.
+
+new() -> [].
+
+fold_fn() ->
+    fun (Event, State) -> fold(Event, State) end.
+
+fold(Event, State) ->
+    case envelope:get_field(type, Event) of
+        {ok, enqueued}      -> fold_enqueued(Event, State);
+        {ok, delivered}     -> fold_delivered(Event, State);
+        {ok, failed}        -> fold_failed(Event, State);
+        {ok, dead_lettered} -> fold_dead_lettered(Event, State);
+        _                   -> State
+    end.
+
+fold_enqueued(Event, State) ->
+    case {envelope:get_field(peer, Event),
+          envelope:get_field(activity, Event)} of
+        {{ok, Peer}, {ok, Act}} ->
+            Worker = ensure_peer(Peer, State),
+            Pending = field(pending, Worker),
+            Worker1 = set_field(pending, Pending ++ [Act], Worker),
+            set_peer(Peer, Worker1, State);
+        _ -> State
+    end.
+
+fold_delivered(Event, State) ->
+    case {envelope:get_field(peer, Event),
+          envelope:get_field(cid, Event)} of
+        {{ok, Peer}, {ok, Cid}} ->
+            case find_keyed(Peer, State) of
+                {ok, Worker} ->
+                    Worker1 = drop_pending_by_cid(Cid, Worker),
+                    Worker2 = clear_retry_for(Cid, Worker1),
+                    set_peer(Peer, Worker2, State);
+                _ -> State
+            end;
+        _ -> State
+    end.
+
+fold_failed(Event, State) ->
+    case {envelope:get_field(peer, Event),
+          envelope:get_field(cid, Event),
+          envelope:get_field(now, Event)} of
+        {{ok, Peer}, {ok, Cid}, {ok, Now}} ->
+            case find_keyed(Peer, State) of
+                {ok, Worker} ->
+                    Attempts = field(attempts, Worker),
+                    Current = case find_keyed(Cid, Attempts) of
+                        {ok, N} -> N;
+                        _ -> 0
+                    end,
+                    New = Current + 1,
+                    Attempts1 = set_keyed(Cid, New, Attempts),
+                    Worker1 = set_field(attempts, Attempts1, Worker),
+                    Worker2 = case delivery_worker:backoff_for(New) of
+                        dead_letter ->
+                            dead_letter_pending(Cid, Worker1);
+                        Seconds ->
+                            NR = field(next_retry, Worker1),
+                            NextAt = Now + Seconds,
+                            set_field(next_retry, set_keyed(Cid, NextAt, NR), Worker1)
+                    end,
+                    set_peer(Peer, Worker2, State);
+                _ -> State
+            end;
+        _ -> State
+    end.
+
+fold_dead_lettered(Event, State) ->
+    case {envelope:get_field(peer, Event),
+          envelope:get_field(cid, Event)} of
+        {{ok, Peer}, {ok, Cid}} ->
+            case find_keyed(Peer, State) of
+                {ok, Worker} ->
+                    set_peer(Peer, dead_letter_pending(Cid, Worker), State);
+                _ -> State
+            end;
+        _ -> State
+    end.
+
+%% ── Accessors ─────────────────────────────────────────────────
+
+peer_state(Peer, State) ->
+    case find_keyed(Peer, State) of
+        {ok, Worker} -> {ok, Worker};
+        _            -> not_found
+    end.
+
+peers(State) -> [P || {P, _} <- State].
+
+pending(Peer, State) ->
+    worker_field(Peer, pending, State, []).
+
+attempts(Peer, State) ->
+    worker_field(Peer, attempts, State, []).
+
+next_retry(Peer, State) ->
+    worker_field(Peer, next_retry, State, []).
+
+dead_letter(Peer, State) ->
+    worker_field(Peer, dead_letter, State, []).
+
+%% ── Internal ──────────────────────────────────────────────────
+
+worker_field(Peer, Field, State, Default) ->
+    case find_keyed(Peer, State) of
+        {ok, Worker} ->
+            case find_keyed(Field, Worker) of
+                {ok, V} -> V;
+                _       -> Default
+            end;
+        _ -> Default
+    end.
+
+ensure_peer(Peer, State) ->
+    case find_keyed(Peer, State) of
+        {ok, Worker} -> Worker;
+        _            -> empty_worker(Peer)
+    end.
+
+empty_worker(Peer) ->
+    [{peer, Peer},
+     {pending, []},
+     {attempts, []},
+     {next_retry, []},
+     {dead_letter, []}].
+
+set_peer(Peer, Worker, State) ->
+    set_keyed(Peer, Worker, State).
+
+drop_pending_by_cid(Cid, Worker) ->
+    Pending = field(pending, Worker),
+    Kept = [A || A <- Pending, activity_cid(A) =/= Cid],
+    set_field(pending, Kept, Worker).
+
+clear_retry_for(Cid, Worker) ->
+    A1 = del_keyed(Cid, field(attempts, Worker)),
+    NR1 = del_keyed(Cid, field(next_retry, Worker)),
+    set_field(attempts, A1, set_field(next_retry, NR1, Worker)).
+
+dead_letter_pending(Cid, Worker) ->
+    Pending = field(pending, Worker),
+    {Match, Rest} = split_by_cid(Cid, Pending),
+    DL = field(dead_letter, Worker),
+    Worker1 = set_field(pending, Rest, Worker),
+    Worker2 = case Match of
+        none -> Worker1;
+        Act  -> set_field(dead_letter, DL ++ [Act], Worker1)
+    end,
+    clear_retry_for(Cid, Worker2).
+
+split_by_cid(Cid, List) -> split_by_cid(Cid, List, []).
+split_by_cid(_, [], Acc) -> {none, lists:reverse(Acc)};
+split_by_cid(Cid, [A | Rest], Acc) ->
+    case activity_cid(A) of
+        Cid -> {A, lists:reverse(Acc) ++ Rest};
+        _   -> split_by_cid(Cid, Rest, [A | Acc])
+    end.
+
+activity_cid(Activity) ->
+    case envelope:get_field(id, Activity) of
+        {ok, Cid} -> Cid;
+        _         -> nil
+    end.
+
+field(K, [{K, V} | _]) -> V;
+field(K, [_ | Rest]) -> field(K, Rest);
+field(_, []) -> undefined.
+
+set_field(K, V, []) -> [{K, V}];
+set_field(K, V, [{K, _} | Rest]) -> [{K, V} | Rest];
+set_field(K, V, [P | Rest]) -> [P | set_field(K, V, Rest)].
+
+find_keyed(_, []) -> {error, not_found};
+find_keyed(K, [{K, V} | _]) -> {ok, V};
+find_keyed(K, [_ | Rest]) -> find_keyed(K, Rest).
+
+set_keyed(K, V, []) -> [{K, V}];
+set_keyed(K, V, [{K, _} | Rest]) -> [{K, V} | Rest];
+set_keyed(K, V, [P | Rest]) -> [P | set_keyed(K, V, Rest)].
+
+del_keyed(_, []) -> [];
+del_keyed(K, [{K, _} | Rest]) -> Rest;
+del_keyed(K, [P | Rest]) -> [P | del_keyed(K, Rest)].

next/kernel/delivery_worker.erl

@@ -0,0 +1,426 @@
+-module(delivery_worker).
+-behaviour(gen_server).
+-export([new/1, pending/1, peer/1,
+         enqueue_pure/3, drain_pure/1, deliver_one_pure/2,
+         backoff_for/1, schedule_for/1,
+         record_failure_pure/3, record_success_pure/2,
+         next_due_pure/2, attempts_for/2, next_retry_at/2,
+         dead_letter_list/1, timer_ref_for/2,
+         start_link/1, start_link/2, stop/1,
+         enqueue/2, flush/1, pending_srv/1, set_dispatch_fn/2,
+         state_srv/1]).
+-export([init/1, handle_call/3, handle_cast/2, handle_info/2]).
+
+%% Outbound delivery worker per design §13.4. One gen_server per
+%% peer instance (peer-id atom) holding a FIFO queue of pending
+%% activities to deliver. v2 lands in stages:
+%%
+%%   Step 8a  pure-functional state shape, enqueue / drain /
+%%            schedule semantics + gen_server skeleton + tests
+%%   Step 8b  retry / backoff schedule (30s / 5m / 30m / 6h / 24h)
+%%            + dead-letter list
+%%   Step 8c  delivery-state projection so the queue survives
+%%            kernel restart
+%%   Step 8d  outbox:publish/2 dispatches each delivery-set entry
+%%            to the matching worker
+%%   Step 8e  httpc:request/4 BIF (substrate exception per briefing)
+%%   Step 8f  real HTTP POST through the BIF + content-type wiring
+%%
+%% This file is 8a only — pure state + skeleton gen_server with the
+%% APIs Step 8b-d will fill in. Real HTTP dispatch is stubbed via a
+%% caller-supplied `:dispatch_fn` so tests can intercept and Step 8f
+%% can plug in the live httpc call without touching the queue logic.
+%%
+%% State shape (pure):
+%%   [{peer, PeerId},
+%%    {pending, [Activity, ...]},          %% FIFO; head delivered first
+%%    {attempts, [{Cid, AttemptCount}, ...]},
+%%    {next_retry, [{Cid, NextRetryAt}, ...]}, %% Step 8b-pure
+%%    {dead_letter, [Activity, ...]},
+%%    {dispatch_fn, fun/1 | undefined}]
+%%
+%% gen_server registers under the peer-id atom (one worker per peer);
+%% the same APIs work as pure-functional state transitions for tests.
+
+%% ── Pure-functional API ─────────────────────────────────────────
+
+new(PeerId) ->
+    [{peer, PeerId},
+     {pending, []},
+     {attempts, []},
+     {next_retry, []},
+     {dead_letter, []},
+     {timers, []},
+     {dispatch_fn, undefined}].
+
+pending(State) -> field(pending, State).
+peer(State) -> field(peer, State).
+
+%% enqueue_pure/3 — append an activity to the queue. Returns new
+%% state. Duplicate :id activities aren't deduplicated here — that's
+%% the caller's job (Step 8d will pass each delivery-set entry once).
+
+enqueue_pure(_PeerId, Activity, State) ->
+    Pending = field(pending, State),
+    set_field(pending, Pending ++ [Activity], State).
+
+%% drain_pure/1 — attempt to deliver every queued activity through
+%% the configured dispatch_fn. Returns {NewState, DeliveredCids,
+%% RetryCids}. Activities that fail dispatch stay in :pending with
+%% an incremented attempt counter — Step 8b will use the count to
+%% pick a backoff slot.
+
+drain_pure(State) ->
+    Pending = field(pending, State),
+    drain_loop(Pending, [], State, [], []).
+
+drain_loop([], Kept, State, Delivered, Retry) ->
+    {set_field(pending, Kept, State), Delivered, Retry};
+drain_loop([A | Rest], Kept, State, Delivered, Retry) ->
+    case deliver_one_pure(A, State) of
+        {ok, Cid} ->
+            drain_loop(Rest, Kept, State, Delivered ++ [Cid], Retry);
+        {error, Cid, _Reason} ->
+            State1 = bump_attempt(Cid, State),
+            drain_loop(Rest, Kept ++ [A], State1, Delivered, Retry ++ [Cid])
+    end.
+
+%% deliver_one_pure/2 — single-activity dispatch via the caller-
+%% supplied dispatch_fn. Returns {ok, Cid} on success or {error,
+%% Cid, Reason} on failure. With no dispatch_fn configured returns
+%% {error, _, no_dispatch_fn} so callers know to wire one before
+%% the worker is useful.
+
+deliver_one_pure(Activity, State) ->
+    Cid = activity_cid(Activity),
+    case field(dispatch_fn, State) of
+        undefined -> {error, Cid, no_dispatch_fn};
+        Fn when is_function(Fn, 1) ->
+            case Fn(Activity) of
+                ok              -> {ok, Cid};
+                {ok, _}         -> {ok, Cid};
+                {error, Reason} -> {error, Cid, Reason};
+                Other           -> {error, Cid, {bad_dispatch_return, Other}}
+            end;
+        _ -> {error, Cid, bad_dispatch_fn}
+    end.
+
+%% backoff_for/1 — Step 8a returns the static schedule per the
+%% plan; Step 8b wires it into the retry loop. Attempts are
+%% 1-indexed (first retry uses slot 1).
+%%
+%%   30s / 5m / 30m / 6h / 24h then dead_letter.
+
+backoff_for(0)              -> 0;
+backoff_for(1)              -> 30;
+backoff_for(2)              -> 300;       % 5 * 60
+backoff_for(3)              -> 1800;      % 30 * 60
+backoff_for(4)              -> 21600;     % 6 * 3600
+backoff_for(5)              -> 86400;     % 24 * 3600
+backoff_for(_)              -> dead_letter.
+
+schedule_for(Attempts) ->
+    case backoff_for(Attempts) of
+        dead_letter -> dead_letter;
+        Seconds     -> {retry_in, Seconds}
+    end.
+
+%% ── Step 8b-pure: retry-time bookkeeping ───────────────────────
+%%
+%% `record_failure_pure/3(Cid, Now, State)` — call after a failed
+%% deliver_one. Bumps the per-cid attempt counter; if the new
+%% attempt is past the dead-letter threshold, moves the matching
+%% activity from :pending to :dead_letter. Otherwise records the
+%% next retry time as Now + backoff_for(NewAttempt).
+%%
+%% Real timer wiring (erlang:send_after self-cast on the worker
+%% pid) needs substrate support — Step 8b-timer when that lands.
+%%
+%% `record_success_pure/2(Cid, State)` — clears :attempts and
+%% :next_retry entries for the cid; called after a successful
+%% deliver_one.
+%%
+%% `next_due_pure/2(Now, State)` — returns the list of Cids whose
+%% NextRetryAt has passed, in insertion order.
+
+record_failure_pure(Cid, Now, State) ->
+    Attempts = field(attempts, State),
+    Current  = case find_keyed(Cid, Attempts) of
+        {ok, N} -> N;
+        _       -> 0
+    end,
+    New = Current + 1,
+    State1 = set_field(attempts, set_keyed(Cid, New, Attempts), State),
+    case backoff_for(New) of
+        dead_letter ->
+            move_to_dead_letter(Cid, State1);
+        Seconds ->
+            NextAt = Now + Seconds,
+            NR = field(next_retry, State1),
+            set_field(next_retry, set_keyed(Cid, NextAt, NR), State1)
+    end.
+
+record_success_pure(Cid, State) ->
+    A1 = del_keyed(Cid, field(attempts, State)),
+    NR1 = del_keyed(Cid, field(next_retry, State)),
+    set_field(attempts, A1, set_field(next_retry, NR1, State)).
+
+%% next_due_pure/2 — Cids whose NextRetryAt <= Now. Preserves
+%% insertion order so the worker drains them in FIFO retry order.
+
+next_due_pure(Now, State) ->
+    [Cid || {Cid, At} <- field(next_retry, State), At =< Now].
+
+attempts_for(Cid, State) ->
+    case find_keyed(Cid, field(attempts, State)) of
+        {ok, N} -> N;
+        _       -> 0
+    end.
+
+next_retry_at(Cid, State) ->
+    case find_keyed(Cid, field(next_retry, State)) of
+        {ok, At} -> At;
+        _        -> undefined
+    end.
+
+dead_letter_list(State) -> field(dead_letter, State).
+
+%% Step 8b-timer: per-cid timer ref accessor. Exposed for tests so
+%% they can assert a retry timer was scheduled (or wasn't, after a
+%% success / dead-letter). Returns the live Ref or undefined.
+
+timer_ref_for(Cid, State) ->
+    case find_keyed(Cid, field(timers, State)) of
+        {ok, Ref} -> Ref;
+        _         -> undefined
+    end.
+
+move_to_dead_letter(Cid, State) ->
+    Pending = field(pending, State),
+    {Match, Rest} = take_by_cid(Cid, Pending, [], []),
+    DL = field(dead_letter, State),
+    State1 = set_field(pending, Rest, State),
+    State2 = case Match of
+        none -> State1;
+        Act  -> set_field(dead_letter, DL ++ [Act], State1)
+    end,
+    NR = field(next_retry, State2),
+    set_field(next_retry, del_keyed(Cid, NR), State2).
+
+take_by_cid(_, [], Acc, _) -> {none, lists:reverse(Acc)};
+take_by_cid(Cid, [A | Rest], Acc, _) ->
+    case activity_cid(A) of
+        Cid -> {A, lists:reverse(Acc) ++ Rest};
+        _   -> take_by_cid(Cid, Rest, [A | Acc], 0)
+    end.
+
+%% ── gen_server wrapper ──────────────────────────────────────────
+
+start_link(PeerId) ->
+    start_link(PeerId, undefined).
+
+start_link(PeerId, DispatchFn) ->
+    Pid = gen_server:start_link(delivery_worker, [PeerId, DispatchFn]),
+    erlang:register(PeerId, Pid),
+    Pid.
+
+stop(PeerId) ->
+    R = gen_server:call(PeerId, '$gen_stop'),
+    erlang:unregister(PeerId),
+    R.
+
+enqueue(PeerId, Activity) ->
+    gen_server:call(PeerId, {enqueue, Activity}).
+
+flush(PeerId) ->
+    gen_server:call(PeerId, flush).
+
+pending_srv(PeerId) ->
+    gen_server:call(PeerId, get_pending).
+
+set_dispatch_fn(PeerId, Fn) ->
+    gen_server:call(PeerId, {set_dispatch_fn, Fn}).
+
+%% Step 8b-timer: return the worker's full state so tests can use the
+%% pure introspection functions (attempts_for / next_retry_at /
+%% timer_ref_for / dead_letter_list) against it.
+
+state_srv(PeerId) ->
+    gen_server:call(PeerId, get_state).
+
+%% gen_server callbacks
+
+init([PeerId, DispatchFn]) ->
+    S0 = new(PeerId),
+    {ok, set_field(dispatch_fn, DispatchFn, S0)}.
+
+handle_call({enqueue, Activity}, _From, State) ->
+    {reply, ok, enqueue_pure(field(peer, State), Activity, State)};
+handle_call(flush, _From, State) ->
+    %% Step 8b-timer: drain (which already bumps :attempts via
+    %% bump_attempt on each failed deliver), then for each retried
+    %% Cid compute the backoff slot from the now-current attempt
+    %% count, set NextRetryAt, and arm a send_after self-cast.
+    %% handle_info({retry, Cid}, ...) fires when the slot elapses.
+    %% Reply shape unchanged.
+    {DrainState, Delivered, Retry} = drain_pure(State),
+    Now = monotonic_seconds(),
+    NewState = lists:foldl(
+        fun(Cid, S) -> arm_retry_timer(Cid, Now, S) end,
+        DrainState, Retry),
+    {reply, {ok, Delivered, Retry}, NewState};
+handle_call(get_pending, _From, State) ->
+    {reply, field(pending, State), State};
+handle_call(get_state, _From, State) ->
+    {reply, State, State};
+handle_call({set_dispatch_fn, Fn}, _From, State) ->
+    {reply, ok, set_field(dispatch_fn, Fn, State)}.
+
+handle_cast(_, S) -> {noreply, S}.
+
+%% Step 8b-timer: a retry timer fired. Pull the activity by Cid from
+%% the pending queue (it might have been drained meanwhile by a
+%% concurrent flush — if so, we just clear bookkeeping and exit).
+%% Run deliver_one_pure: success clears retry state; failure bumps
+%% the counter and schedules the next slot — or dead-letters if the
+%% sixth attempt failed.
+
+handle_info({retry, Cid}, State) ->
+    %% Clear the timer ref we just consumed.
+    State0 = clear_timer_ref(Cid, State),
+    case take_by_cid(Cid, field(pending, State0), [], 0) of
+        {none, _} ->
+            %% Already drained / dead-lettered. Clear any stale
+            %% bookkeeping in case the cid is half-tracked.
+            {noreply, record_success_pure(Cid, State0)};
+        {Activity, Rest} ->
+            case deliver_one_pure(Activity, State0) of
+                {ok, _} ->
+                    State1 = set_field(pending, Rest, State0),
+                    State2 = record_success_pure(Cid, State1),
+                    {noreply, State2};
+                {error, _, _} ->
+                    %% Keep the activity in pending; record_failure
+                    %% leaves :pending alone (or dead-letters it on
+                    %% slot 6).
+                    Now = monotonic_seconds(),
+                    State1 = schedule_retry_for(Cid, Now, State0),
+                    {noreply, State1}
+            end
+    end;
+handle_info(_, S) -> {noreply, S}.
+
+%% Step 8b-timer helpers ────────────────────────────────────────────
+
+%% arm_retry_timer/3 — POST-DRAIN form. Used from handle_call(flush)
+%% after drain_pure has already bumped :attempts via bump_attempt.
+%% Sets next_retry_at = Now + backoff(attempts) and schedules the
+%% send_after self-cast. On the dead-letter slot (attempt 6), moves
+%% the activity from :pending to :dead_letter and arms no timer.
+
+arm_retry_timer(Cid, Now, State) ->
+    State0 = cancel_timer_for(Cid, State),
+    Attempts = attempts_for(Cid, State0),
+    case backoff_for(Attempts) of
+        dead_letter ->
+            move_to_dead_letter(Cid, State0);
+        Seconds ->
+            NextAt = Now + Seconds,
+            NR = field(next_retry, State0),
+            State1 = set_field(next_retry, set_keyed(Cid, NextAt, NR), State0),
+            Ms = Seconds * 1000,
+            Ref = erlang:send_after(Ms, self(), {retry, Cid}),
+            Timers = field(timers, State1),
+            set_field(timers, set_keyed(Cid, Ref, Timers), State1)
+    end.
+
+%% schedule_retry_for/3 — POST-RETRY-ATTEMPT form. Used from
+%% handle_info({retry, Cid}, ...) when the retry attempt failed.
+%% Bookkeep one failure and arm the next retry timer (or promote
+%% to dead-letter, in which case no timer is needed).
+
+schedule_retry_for(Cid, Now, State) ->
+    %% Cancel any in-flight timer for this Cid before scheduling a new
+    %% one. Without the cancel a stale timer can still fire after
+    %% record_success has cleared the cid, the handle_info no-match
+    %% branch silently absorbs it — but it keeps the scheduler's
+    %% run-loop alive long after the work is done. A pure clear (no
+    %% cancel) is fine when the timer's own firing brought us here,
+    %% so the explicit cancel only matters for the flush path.
+    State0 = cancel_timer_for(Cid, State),
+    State1 = record_failure_pure(Cid, Now, State0),
+    Attempts = attempts_for(Cid, State1),
+    case backoff_for(Attempts) of
+        dead_letter ->
+            State1;
+        Seconds ->
+            Ms = Seconds * 1000,
+            Ref = erlang:send_after(Ms, self(), {retry, Cid}),
+            Timers = field(timers, State1),
+            set_field(timers, set_keyed(Cid, Ref, Timers), State1)
+    end.
+
+%% Cancel the live timer for Cid (if any) and clear it from :timers.
+%% Idempotent — silent no-op if there isn't one.
+
+cancel_timer_for(Cid, State) ->
+    Timers = field(timers, State),
+    case find_keyed(Cid, Timers) of
+        {ok, Ref} ->
+            erlang:cancel_timer(Ref),
+            set_field(timers, del_keyed(Cid, Timers), State);
+        _ -> State
+    end.
+
+%% Drop the :timers entry for Cid without calling cancel_timer — used
+%% when the timer's own firing brought us into handle_info and the ref
+%% is already consumed.
+
+clear_timer_ref(Cid, State) ->
+    Timers = field(timers, State),
+    case find_keyed(Cid, Timers) of
+        {ok, _Ref} -> set_field(timers, del_keyed(Cid, Timers), State);
+        _          -> State
+    end.
+
+%% Step 8b-timer: bookkeeping uses seconds (matches backoff_for /
+%% record_failure_pure / next_retry_at). The monotonic clock reports
+%% ms; we floor to seconds here to keep all the comparisons aligned.
+
+monotonic_seconds() -> erlang:monotonic_time() div 1000.
+
+%% ── Internal ────────────────────────────────────────────────────
+
+activity_cid(Activity) ->
+    case envelope:get_field(id, Activity) of
+        {ok, Cid} -> Cid;
+        _         -> nil
+    end.
+
+bump_attempt(Cid, State) ->
+    Attempts = field(attempts, State),
+    Current = case find_keyed(Cid, Attempts) of
+        {ok, N}     -> N;
+        _           -> 0
+    end,
+    set_field(attempts, set_keyed(Cid, Current + 1, Attempts), State).
+
+field(K, [{K, V} | _]) -> V;
+field(K, [_ | Rest]) -> field(K, Rest);
+field(_, []) -> undefined.
+
+set_field(K, V, []) -> [{K, V}];
+set_field(K, V, [{K, _} | Rest]) -> [{K, V} | Rest];
+set_field(K, V, [P | Rest]) -> [P | set_field(K, V, Rest)].
+
+find_keyed(_, []) -> {error, not_found};
+find_keyed(K, [{K, V} | _]) -> {ok, V};
+find_keyed(K, [_ | Rest]) -> find_keyed(K, Rest).
+
+set_keyed(K, V, []) -> [{K, V}];
+set_keyed(K, V, [{K, _} | Rest]) -> [{K, V} | Rest];
+set_keyed(K, V, [P | Rest]) -> [P | set_keyed(K, V, Rest)].
+
+del_keyed(_, []) -> [];
+del_keyed(K, [{K, _} | Rest]) -> Rest;
+del_keyed(K, [P | Rest]) -> [P | del_keyed(K, Rest)].

next/kernel/discovery.erl

@@ -0,0 +1,98 @@
+-module(discovery).
+-export([parse_acct/1, parse_resource/1,
+         actor_url_for/2, webfinger_body/3]).
+
+%% Discovery primitives per design §13.7. Step 10a covers the
+%% local-side webfinger endpoint (responding when a peer asks
+%% "where does acct:alice@here live?"); the peer-fetch direction
+%% (loading a peer's actor doc lazily on first inbound) is Step 10b
+%% and gates on Blockers #2 (native http-request primitive).
+%%
+%% parse_acct/1 — accept a binary in either form:
+%%   <<"acct:alice@host:port">>   (full prefixed URI)
+%%   <<"alice@host:port">>         (bare account, prefix optional)
+%% Returns {ok, User, Host} | {error, Reason}.
+%%
+%% parse_resource/1 — the resource= query parameter from
+%% /.well-known/webfinger. Same shape as parse_acct.
+%%
+%% actor_url_for/2(User, Host) — synthesises the canonical
+%% per-actor URL `<scheme>://<host>/actors/<user>`. v2 hardcodes
+%% http://; TLS / https is v3 (Blockers gate).
+%%
+%% webfinger_body/3 — builds the JSON response body.
+
+%% ── parse_acct / parse_resource ─────────────────────────────────
+
+%% "acct:" -> 5 bytes: 97 99 99 116 58
+parse_acct(Bin) when is_binary(Bin) ->
+    AcctPrefix = <<97,99,99,116,58>>,
+    case strip_prefix(AcctPrefix, Bin) of
+        {ok, Rest} -> split_user_host(Rest);
+        nomatch    -> split_user_host(Bin)
+    end;
+parse_acct(_) -> {error, bad_input}.
+
+parse_resource(Bin) -> parse_acct(Bin).
+
+%% strip_prefix/2 — return {ok, Rest} when Bin starts with Prefix,
+%% else nomatch. Substrate has no proper prefix-match BIF; this
+%% byte-walks.
+
+strip_prefix(<<>>, Rest) -> {ok, Rest};
+strip_prefix(<<B, PRest/binary>>, <<B, RRest/binary>>) ->
+    strip_prefix(PRest, RRest);
+strip_prefix(_, _) -> nomatch.
+
+%% split_user_host/1 — split a `user@host[:port]` binary at the
+%% first `@`. Returns {ok, User, Host} where Host may include the
+%% optional port suffix.
+
+split_user_host(Bin) ->
+    case split_at(64, Bin) of  % 64 = '@'
+        {Before, After} when byte_size(Before) > 0, byte_size(After) > 0 ->
+            {ok, Before, After};
+        _ ->
+            {error, bad_acct}
+    end.
+
+split_at(Byte, Bin) ->
+    split_at(Byte, Bin, <<>>).
+
+split_at(_, <<>>, Acc) ->
+    {Acc, <<>>};
+split_at(Byte, <<Byte, Rest/binary>>, Acc) ->
+    {Acc, Rest};
+split_at(Byte, <<B, Rest/binary>>, Acc) ->
+    split_at(Byte, Rest, <<Acc/binary, B>>).
+
+%% ── URL synthesis ──────────────────────────────────────────────
+
+%% "http://"  -> 7 bytes  | "/actors/" -> 8 bytes
+actor_url_for(User, Host) ->
+    Pre = <<104,116,116,112,58,47,47>>,            % "http://"
+    Mid = <<47,97,99,116,111,114,115,47>>,         % "/actors/"
+    <<Pre/binary, Host/binary, Mid/binary, User/binary>>.
+
+%% ── webfinger JSON body ────────────────────────────────────────
+%%
+%% Mastodon-shape per RFC 7033:
+%%   {"subject":"acct:<user>@<host>",
+%%    "links":[{"rel":"self",
+%%              "type":"application/activity+json",
+%%              "href":"<actor_url>"}]}
+%%
+%% Hand-rolled byte concatenation — no JSON BIF on this port. The
+%% caller has already validated User + Host; we don't need to
+%% re-escape (Mastodon's webfinger inputs are alphanumeric +
+%% .-_ in practice).
+
+webfinger_body(User, Host, ActorUrl) ->
+    AcctPre = <<123,34,115,117,98,106,101,99,116,34,58,34,97,99,99,116,58>>,  % '{"subject":"acct:'
+    AcctAt  = <<64>>,                                                          % '@'
+    LinksHd = <<34,44,34,108,105,110,107,115,34,58,91,123,34,114,101,108,34,58,34,115,101,108,102,34,44,
+                34,116,121,112,101,34,58,34,97,112,112,108,105,99,97,116,105,111,110,47,97,99,116,
+                105,118,105,116,121,43,106,115,111,110,34,44,34,104,114,101,102,34,58,34>>,         % '","links":[{"rel":"self","type":"application/activity+json","href":"'
+    LinksTl = <<34,125,93,125,10>>,                                            % '"}]}\n'
+    <<AcctPre/binary, User/binary, AcctAt/binary, Host/binary,
+      LinksHd/binary, ActorUrl/binary, LinksTl/binary>>.

next/kernel/discovery_fetch.erl

@@ -0,0 +1,89 @@
+-module(discovery_fetch).
+-export([make_fetch_fn/1,
+         fetch/2,
+         actor_doc_url/2,
+         decode_body/1,
+         accept_header/0]).
+
+%% Live peer-actor-doc fetch for peer_actors — Step 10c per design
+%% §13.6. The peer_actors gen_server already exposes
+%% lookup_or_fetch_srv/2(PeerId, FetchFn) where FetchFn is a
+%% 1-arity closure that returns {ok, PeerAS} | {error, Reason} on
+%% cache miss. For tests we wire a fake FetchFn that returns a
+%% pre-baked AS; for live federation we wire the closure this
+%% module produces — it GETs <base>/actors/<peer> with an Accept
+%% header that asks for the actor_doc format
+%% (http_server.erl Step 10c), decodes the response body via
+%% term_codec, and returns the AS proplist.
+%%
+%% Cfg shape (reuses dispatch_http's peer URL resolution so a
+%% single Cfg threads through both delivery and discovery):
+%%   {peer_url,    [{PeerId, BaseUrl}, ...]}
+%%   {peer_url_fn, fun ((PeerId) -> {ok, BaseUrl} | not_found)}
+%%
+%% BaseUrl shape: <<"http://host:port">> (no trailing slash; this
+%% module appends the path). PeerId is the actor atom.
+%%
+%% Outcomes:
+%%   2xx + decodable body -> {ok, PeerAS}
+%%   2xx + bad body       -> {error, bad_actor_doc}
+%%   non-2xx              -> {error, {status, N}}
+%%   resolver miss        -> {error, no_peer_url}
+%%   transport            -> {error, Reason}
+%%
+%% Cache write semantics live in peer_actors:lookup_or_fetch/3 —
+%% successful fetches store; errors do NOT poison so callers can
+%% retry on transients.
+
+%% ── Accept header ────────────────────────────────────────────
+%% "application/vnd.fed-sx.actor-doc" — same MIME the http_server
+%% content_type_for(actor_doc) emits, so the Accept negotiation
+%% in accept_format/1 routes the peer's response to the term_codec
+%% serializer arm.
+accept_header() ->
+    <<97,112,112,108,105,99,97,116,105,111,110,47,
+      118,110,100,46,102,101,100,45,115,120,46,
+      97,99,116,111,114,45,100,111,99>>.
+
+%% ── public API ───────────────────────────────────────────────
+
+make_fetch_fn(Cfg) ->
+    fun (PeerId) ->
+        case dispatch_http:resolve_peer_url(PeerId, Cfg) of
+            {error, R}    -> {error, R};
+            {ok, BaseUrl} -> fetch(actor_doc_url(BaseUrl, PeerId), Cfg)
+        end
+    end.
+
+fetch(Url, _Cfg) ->
+    AcceptKey = <<97,99,99,101,112,116>>,  % "accept"
+    Headers = [{AcceptKey, accept_header()}],
+    try httpc:request(Url, get, Headers, <<>>) of
+        {ok, Status, _H, Body} when Status >= 200, Status < 300 ->
+            decode_body(Body);
+        {ok, Status, _H, _B} ->
+            {error, {status, Status}};
+        Other ->
+            {error, {bad_response, Other}}
+    catch
+        error:Reason -> {error, Reason}
+    end.
+
+%% actor_doc_url/2 — <BaseUrl>/actors/<peer>. PeerId is the actor
+%% atom; rendered to a binary via its name (matches the same path
+%% layout http_server.erl uses for the route registration at
+%% prefix "/actors/").
+actor_doc_url(BaseUrl, PeerId) when is_atom(PeerId) ->
+    PeerBin = list_to_binary(atom_to_list(PeerId)),
+    %% "/actors/" — 8 bytes
+    Prefix = <<47,97,99,116,111,114,115,47>>,
+    <<BaseUrl/binary, Prefix/binary, PeerBin/binary>>.
+
+%% decode_body/1 — round the wire body back through term_codec.
+%% Returns {ok, AS} on a proplist-shaped decode (matching the
+%% peer-actor-state schema), {error, bad_actor_doc} otherwise.
+decode_body(Body) ->
+    case term_codec:decode(Body) of
+        {ok, AS, _} when is_list(AS) -> {ok, AS};
+        _ -> {error, bad_actor_doc}
+    end.

next/kernel/dispatch_http.erl

@@ -0,0 +1,119 @@
+-module(dispatch_http).
+-export([make_dispatch_fn/2,
+         dispatch/3,
+         inbox_url/2,
+         resolve_peer_url/2,
+         content_type/0]).
+
+%% Live HTTP dispatch for delivery_worker — Step 8f per design §13.4.
+%%
+%% delivery_worker takes an opaque `dispatch_fn :: fun(Activity) ->
+%% ok | {ok, _} | {error, Reason}`. For tests we wire a fake one
+%% that records calls; for live federation we wire the closure this
+%% module produces — a 1-arity fun that encodes the activity with
+%% term_codec, looks up the peer's URL base, and POSTs to
+%% `<base>/actors/<peer>/inbox` via httpc:request/4 (the BIF
+%% wrapper Step 8e landed in lib/erlang/runtime.sx around the
+%% native http-request primitive from fed-prims).
+%%
+%% Cfg shape (composable, priority order):
+%%   {peer_url, [{PeerId, BaseUrl::binary}, ...]}
+%%       Static map; tests + small static deployments. PeerId is
+%%       the actor atom (alice / bob / ...).
+%%   {peer_url_fn, fun((PeerId) -> {ok, BaseUrl} | not_found)}
+%%       Dynamic lookup; used when peer_actors gen_server caches a
+%%       discovery result (Step 10c will plumb this).
+%%
+%% BaseUrl is the scheme+host+port of the peer's HTTP server, e.g.
+%% <<"http://127.0.0.1:8123">>. The inbox URL is built by
+%% appending /actors/<peer>/inbox so callers don't have to know the
+%% wire path layout.
+%%
+%% Dispatch outcome:
+%%   2xx           -> ok               (delivery_worker drops the entry)
+%%   non-2xx       -> {error, {status, N}}
+%%   resolver miss -> {error, no_peer_url}
+%%   transport     -> {error, Reason}   (BIF-raised, caught here)
+
+%% ── content-type ─────────────────────────────────────────────
+%% "application/vnd.fed-sx.activity" — picked to be distinct from
+%% the existing http_server content types (text/json/sx/cbor) since
+%% the wire bytes are term_codec's custom netstring-ish format, not
+%% any of them. The receiver's handle_inbox_post/3 in
+%% http_server.erl doesn't gate on content-type yet; it just hands
+%% the body to term_codec:decode. We still send a real MIME so
+%% intermediaries (proxies, load balancers, logs) see something
+%% honest. Substrate Note: M2 doesn't add a content_type_for/1
+%% clause to http_server because that's serving outbound responses
+%% (the dispatch direction is FROM us; the receiver shapes its
+%% own response).
+content_type() ->
+    %% "application/vnd.fed-sx.activity"
+    <<97,112,112,108,105,99,97,116,105,111,110,47,
+      118,110,100,46,102,101,100,45,115,120,46,97,99,
+      116,105,118,105,116,121>>.
+
+%% ── public API ───────────────────────────────────────────────
+
+make_dispatch_fn(PeerId, Cfg) ->
+    fun (Activity) ->
+        case resolve_peer_url(PeerId, Cfg) of
+            {error, R} ->
+                {error, R};
+            {ok, BaseUrl} ->
+                Url = inbox_url(BaseUrl, PeerId),
+                dispatch(Url, Activity, Cfg)
+        end
+    end.
+
+dispatch(Url, Activity, _Cfg) ->
+    Body = term_codec:encode(Activity),
+    Headers = [{<<99,111,110,116,101,110,116,45,116,121,112,101>>,
+                content_type()}],
+    %% This port's try/catch needs a literal class atom (not Class:R).
+    %% The BIF wrapper raises error:{network, _} on transport failure
+    %% and error:badarg on shape failure; both reach us as `error`.
+    try httpc:request(Url, post, Headers, Body) of
+        {ok, Status, _H, _B} when Status >= 200, Status < 300 -> ok;
+        {ok, Status, _H, _B} -> {error, {status, Status}};
+        Other -> {error, {bad_response, Other}}
+    catch
+        error:Reason -> {error, Reason}
+    end.
+
+%% inbox_url/2 — concatenate BaseUrl + "/actors/" + PeerId + "/inbox".
+%% PeerId is the actor atom; rendered to a binary via its name.
+inbox_url(BaseUrl, PeerId) when is_atom(PeerId) ->
+    PeerBin = list_to_binary(atom_to_list(PeerId)),
+    %% "/actors/" — 47,97,99,116,111,114,115,47
+    Prefix = <<47,97,99,116,111,114,115,47>>,
+    %% "/inbox" — 47,105,110,98,111,120
+    Suffix = <<47,105,110,98,111,120>>,
+    <<BaseUrl/binary, Prefix/binary, PeerBin/binary, Suffix/binary>>.
+
+%% resolve_peer_url/2 — static :peer_url map first (tests), then
+%% :peer_url_fn closure (Step 10c will hand one in once peer_actors
+%% caches discovered URLs).
+resolve_peer_url(PeerId, Cfg) ->
+    case envelope:get_field(peer_url, Cfg) of
+        {ok, Map} when is_list(Map) ->
+            case lookup_peer(PeerId, Map) of
+                {ok, U} -> {ok, U};
+                _       -> try_fn(PeerId, Cfg)
+            end;
+        _ -> try_fn(PeerId, Cfg)
+    end.
+
+try_fn(PeerId, Cfg) ->
+    case envelope:get_field(peer_url_fn, Cfg) of
+        {ok, Fn} when is_function(Fn, 1) ->
+            case Fn(PeerId) of
+                {ok, U} when is_binary(U) -> {ok, U};
+                _ -> {error, no_peer_url}
+            end;
+        _ -> {error, no_peer_url}
+    end.
+
+lookup_peer(_PeerId, []) -> not_found;
+lookup_peer(PeerId, [{PeerId, Url} | _]) -> {ok, Url};
+lookup_peer(PeerId, [_ | Rest]) -> lookup_peer(PeerId, Rest).

next/kernel/endorsement_state.erl

@@ -0,0 +1,118 @@
+-module(endorsement_state).
+-export([new/0, fold/2, fold_fn/0,
+         counters_for/2, total_for/2, kinds_for/2,
+         endorsers_for/3, has_endorsed/4]).
+
+%% Endorsement counter projection. Folds Endorse activities into a
+%% per-target-Cid + per-kind counter so projections can serve
+%% "how many likes does this Note have" / "list everyone who shared
+%% this Announce" queries.
+%%
+%% Endorse envelope shape (per next/genesis/activity-types/endorse.sx):
+%%   [{type, endorse},
+%%    {actor, ActorId},
+%%    {object, TargetCidBinary},
+%%    {kind, KindAtomOrBinary},
+%%    ...]
+%%
+%% State shape:
+%%   [{TargetCid, [{Kind, [{ActorId, Count}, ...]}, ...]}, ...]
+%%
+%% Each ActorId can endorse the same target multiple times under
+%% the same kind (e.g. like → unlike → like → ...); the counter
+%% tracks how many *net* endorsement events fired. Step 11b ships
+%% the additive counter only; the unlike / un-endorse semantics
+%% (Undo{Endorse}) and reaction-toggling defer to a follow-up.
+
+new() -> [].
+
+fold_fn() ->
+    fun (Activity, State) -> fold(Activity, State) end.
+
+fold(Activity, State) ->
+    case envelope:get_field(type, Activity) of
+        {ok, endorse} -> fold_endorse(Activity, State);
+        _             -> State
+    end.
+
+fold_endorse(Activity, State) ->
+    case {envelope:get_field(actor, Activity),
+          envelope:get_field(object, Activity),
+          envelope:get_field(kind, Activity)} of
+        {{ok, Actor}, {ok, Cid}, {ok, Kind}} ->
+            bump(Cid, Kind, Actor, State);
+        _ ->
+            State
+    end.
+
+bump(Cid, Kind, Actor, State) ->
+    KindMap = case find_keyed(Cid, State) of
+        {ok, KM} -> KM;
+        _        -> []
+    end,
+    ActorMap = case find_keyed(Kind, KindMap) of
+        {ok, AM} -> AM;
+        _        -> []
+    end,
+    Current = case find_keyed(Actor, ActorMap) of
+        {ok, N} -> N;
+        _       -> 0
+    end,
+    ActorMap1 = set_keyed(Actor, Current + 1, ActorMap),
+    KindMap1  = set_keyed(Kind, ActorMap1, KindMap),
+    set_keyed(Cid, KindMap1, State).
+
+%% ── Read-side accessors ───────────────────────────────────────
+
+%% counters_for(Cid, State) -> [{Kind, TotalCount}, ...]
+%% Sum per-kind across all endorsers.
+
+counters_for(Cid, State) ->
+    case find_keyed(Cid, State) of
+        {ok, KindMap} ->
+            [{K, sum_counts(AM)} || {K, AM} <- KindMap];
+        _ -> []
+    end.
+
+total_for(Cid, State) ->
+    lists:foldl(fun ({_, N}, Acc) -> N + Acc end, 0, counters_for(Cid, State)).
+
+kinds_for(Cid, State) ->
+    [K || {K, _} <- counters_for(Cid, State)].
+
+endorsers_for(Cid, Kind, State) ->
+    case find_keyed(Cid, State) of
+        {ok, KindMap} ->
+            case find_keyed(Kind, KindMap) of
+                {ok, AM} -> [A || {A, _} <- AM];
+                _        -> []
+            end;
+        _ -> []
+    end.
+
+has_endorsed(Actor, Cid, Kind, State) ->
+    case find_keyed(Cid, State) of
+        {ok, KindMap} ->
+            case find_keyed(Kind, KindMap) of
+                {ok, AM} ->
+                    case find_keyed(Actor, AM) of
+                        {ok, N} -> N > 0;
+                        _       -> false
+                    end;
+                _ -> false
+            end;
+        _ -> false
+    end.
+
+%% ── Internal ──────────────────────────────────────────────────
+
+sum_counts([]) -> 0;
+sum_counts([{_, N} | Rest]) -> N + sum_counts(Rest).
+
+find_keyed(_, []) -> {error, not_found};
+find_keyed(K, [{K, V} | _]) -> {ok, V};
+find_keyed(K, [_ | Rest]) -> find_keyed(K, Rest).
+
+set_keyed(K, V, []) -> [{K, V}];
+set_keyed(K, V, [{K, _} | Rest]) -> [{K, V} | Rest];
+set_keyed(K, V, [P | Rest]) -> [P | set_keyed(K, V, Rest)].

next/kernel/envelope.erl

@@ -0,0 +1,177 @@
+-module(envelope).
+-export([validate_shape/1, get_field/2, canonical_bytes/1, verify_signature/2]).
+
+%% Activity envelope per design §3.1.
+%%
+%% Erlang maps (#{...}) are not supported by this port, so envelopes
+%% are represented as property lists of {atom_key, value} pairs. This
+%% port's binary syntax also can't carry string literals; values that
+%% would naturally be binaries in real Erlang are kept as atoms or
+%% integer-segment binaries in the test corpus.
+%%
+%% Required fields: id, type, actor, published, signature.
+%% The signature value is itself a property list with key_id,
+%% algorithm, value.
+%%
+%% validate_shape/1 returns ok | {error, Reason}. Reasons:
+%%   not_a_proplist
+%%   {missing_field, FieldName}
+%%   {bad_signature, BadSigReason}
+%%
+%% get_field/2 returns {ok, Value} | not_found.
+
+validate_shape(Env) when is_list(Env) ->
+    case check_required([id, type, actor, published, signature], Env) of
+        ok -> validate_signature_shape(Env);
+        Err -> Err
+    end;
+validate_shape(_) ->
+    {error, not_a_proplist}.
+
+get_field(_, []) -> not_found;
+get_field(K, [{K, V} | _]) -> {ok, V};
+get_field(K, [_ | Rest]) -> get_field(K, Rest).
+
+check_required([], _) -> ok;
+check_required([F | Rest], Env) ->
+    case get_field(F, Env) of
+        {ok, _} -> check_required(Rest, Env);
+        not_found -> {error, {missing_field, F}}
+    end.
+
+validate_signature_shape(Env) ->
+    {ok, Sig} = get_field(signature, Env),
+    case is_list(Sig) of
+        true ->
+            case check_required([key_id, algorithm, value], Sig) of
+                ok -> ok;
+                {error, {missing_field, F}} ->
+                    {error, {bad_signature, {missing_field, F}}}
+            end;
+        false ->
+            {error, {bad_signature, not_a_proplist}}
+    end.
+
+%% canonical_bytes/1 — the byte string the signature covers.
+%%
+%% Real fed-sx will use dag-cbor over a JSON-LD-canonicalised form
+%% (design §3.2). For milestone 1 we stand in for that with the host
+%% BIF `cid:to_string/1`, which produces a CIDv1 over the deterministic
+%% textual form of the term. Two prior steps make this work:
+%%   1. The signature pair is stripped (sig covers everything except
+%%      itself).
+%%   2. The top-level property list is sorted by key so field order in
+%%      the source envelope is not load-bearing.
+%%
+%% The result is an Erlang binary suitable as the sig-cover input.
+
+canonical_bytes(Env) when is_list(Env) ->
+    Stripped = strip_signature(Env),
+    Sorted = sort_pairs(Stripped),
+    cid:to_string(Sorted).
+
+strip_signature([]) -> [];
+strip_signature([{signature, _} | Rest]) -> strip_signature(Rest);
+strip_signature([P | Rest]) -> [P | strip_signature(Rest)].
+
+sort_pairs([]) -> [];
+sort_pairs([H | T]) -> insert_pair(H, sort_pairs(T)).
+
+insert_pair(P, []) -> [P];
+insert_pair({K1, V1}, [{K2, V2} | Rest]) ->
+    case K1 < K2 of
+        true  -> [{K1, V1}, {K2, V2} | Rest];
+        false -> [{K2, V2} | insert_pair({K1, V1}, Rest)]
+    end.
+
+%% verify_signature/2 — time-aware sig verification per design §9.6.
+%%
+%% Activity carries a `signature` proplist with `key_id`, `algorithm`,
+%% `value`. ActorState carries `public_keys` — a list of key proplists
+%% with `id`, `created`, optionally `superseded_at`, and `value` (the
+%% key material).
+%%
+%% A key is active at time T iff `created =< T` AND
+%% (no `superseded_at` OR T < `superseded_at`). Verification picks the
+%% first matching active key whose `id == signature.key_id` at the
+%% activity's `published` timestamp, then recomputes the MAC
+%% `crypto:hash(sha256, <<KeyMaterial/binary, CanonicalBytes/binary>>)`
+%% and compares it to `signature.value`.
+%%
+%% Returns ok | {error, Reason}. Reasons:
+%%   no_signature | no_key_id | no_published | no_keys |
+%%   no_active_key | bad_signature
+%%
+%% Real RSA-SHA256 / Ed25519 verification is deferred to milestone 2:
+%% Phase 8 only ships `crypto:hash/2`, so we stand in with an HMAC-shaped
+%% MAC that exercises the same key-lookup and canonical-bytes pipeline.
+
+verify_signature(Activity, ActorState) ->
+    case get_field(signature, Activity) of
+        not_found -> {error, no_signature};
+        {ok, Sig} ->
+            case get_field(key_id, Sig) of
+                not_found -> {error, no_key_id};
+                {ok, KeyId} ->
+                    case get_field(published, Activity) of
+                        not_found -> {error, no_published};
+                        {ok, Published} ->
+                            verify_with_keys(Activity, Sig, KeyId,
+                                             Published, ActorState)
+                    end
+            end
+    end.
+
+verify_with_keys(Activity, Sig, KeyId, Published, ActorState) ->
+    case get_field(public_keys, ActorState) of
+        not_found -> {error, no_keys};
+        {ok, Keys} ->
+            case find_active_key(KeyId, Published, Keys) of
+                not_found -> {error, no_active_key};
+                {ok, Key} -> verify_mac(Activity, Sig, Key)
+            end
+    end.
+
+find_active_key(_, _, []) -> not_found;
+find_active_key(KeyId, Now, [Key | Rest]) ->
+    case is_matching_active_key(Key, KeyId, Now) of
+        true -> {ok, Key};
+        false -> find_active_key(KeyId, Now, Rest)
+    end.
+
+is_matching_active_key(Key, WantId, Now) ->
+    case get_field(id, Key) of
+        {ok, WantId} -> is_active_at(Key, Now);
+        _ -> false
+    end.
+
+is_active_at(Key, Now) ->
+    case get_field(created, Key) of
+        not_found -> false;
+        {ok, Created} ->
+            case Now >= Created of
+                false -> false;
+                true ->
+                    case get_field(superseded_at, Key) of
+                        not_found -> true;
+                        {ok, SupAt} -> Now < SupAt
+                    end
+            end
+    end.
+
+verify_mac(Activity, Sig, Key) ->
+    case get_field(value, Sig) of
+        not_found -> {error, bad_signature};
+        {ok, SigValue} ->
+            case get_field(value, Key) of
+                not_found -> {error, bad_signature};
+                {ok, KeyMat} ->
+                    Bytes = canonical_bytes(Activity),
+                    Computed = crypto:hash(sha256,
+                        <<KeyMat/binary, Bytes/binary>>),
+                    case SigValue =:= Computed of
+                        true -> ok;
+                        false -> {error, bad_signature}
+                    end
+            end
+    end.

next/kernel/follower_graph.erl

@@ -0,0 +1,237 @@
+-module(follower_graph).
+-export([fold/2, fold_fn/0, new/0, lookup/2, actors/1,
+         following/2, followers/2,
+         pending_outbound/2, pending_inbound/2,
+         is_following/3, has_follower/3,
+         is_pending_outbound/3, is_pending_inbound/3]).
+
+%% Follower-graph projection — Erlang-fun stand-in for the genesis
+%% `follower-graph.sx` body. Tracks per-actor follow relationships
+%% per design §13.2:
+%%
+%%   Follow {actor: A, object: B}      A asks to follow B
+%%   Accept {actor: B, object: F}      B accepts A's Follow F (= F.actor → F.object)
+%%   Reject {actor: B, object: F}      B rejects A's Follow F
+%%   Undo   {actor: A, object: F}      A retracts F or unfollows
+%%
+%% Where F = Follow{A→B} is embedded as the activity's :object
+%% proplist for Accept / Reject / Undo.
+%%
+%% State shape:
+%%   [{ActorId, ActorEntry}, ...]
+%%
+%% ActorEntry = [{following,        [PeerId, ...]},
+%%               {followers,        [PeerId, ...]},
+%%               {pending_outbound, [PeerId, ...]},  %% I asked, no answer yet
+%%               {pending_inbound,  [PeerId, ...]}]  %% asked me, I haven't answered
+%%
+%% Sets keep insertion order; duplicates aren't added. lists:keyfind/
+%% keymember aren't in this substrate, so local find_keyed/has_keyed/
+%% set_keyed helpers (same convention as actor_state, define_registry,
+%% nx_kernel).
+
+%% ── Public API ──────────────────────────────────────────────────
+
+new() -> [].
+
+actors(State) -> [Id || {Id, _Entry} <- State].
+
+lookup(ActorId, State) ->
+    case find_keyed(ActorId, State) of
+        {ok, Entry} -> {ok, Entry};
+        _           -> not_found
+    end.
+
+following(ActorId, State)        -> entry_field(ActorId, following, State).
+followers(ActorId, State)        -> entry_field(ActorId, followers, State).
+pending_outbound(ActorId, State) -> entry_field(ActorId, pending_outbound, State).
+pending_inbound(ActorId, State)  -> entry_field(ActorId, pending_inbound, State).
+
+is_following(ActorId, PeerId, State) ->
+    contains(PeerId, following(ActorId, State)).
+
+has_follower(ActorId, PeerId, State) ->
+    contains(PeerId, followers(ActorId, State)).
+
+is_pending_outbound(ActorId, PeerId, State) ->
+    contains(PeerId, pending_outbound(ActorId, State)).
+
+is_pending_inbound(ActorId, PeerId, State) ->
+    contains(PeerId, pending_inbound(ActorId, State)).
+
+%% ── Fold dispatch ───────────────────────────────────────────────
+
+fold(Activity, State) ->
+    case envelope:get_field(type, Activity) of
+        {ok, follow} -> fold_follow(Activity, State);
+        {ok, accept} -> fold_accept(Activity, State);
+        {ok, reject} -> fold_reject(Activity, State);
+        {ok, undo}   -> fold_undo(Activity, State);
+        _            -> State
+    end.
+
+fold_fn() ->
+    fun (Activity, State) -> fold(Activity, State) end.
+
+%% Follow {actor: A, object: B}:
+%%   add B to A's pending_outbound
+%%   add A to B's pending_inbound
+fold_follow(Activity, State) ->
+    case follow_actor_object(Activity) of
+        {ok, A, B} when A =/= B ->
+            S1 = add_to_field(A, pending_outbound, B, State),
+            add_to_field(B, pending_inbound, A, S1);
+        _ -> State
+    end.
+
+%% Accept {actor: B, object: Follow{A→B}}:
+%%   move A from B's pending_inbound to B's followers
+%%   move B from A's pending_outbound to A's following
+fold_accept(Activity, State) ->
+    case nested_follow_actor_object(Activity) of
+        {ok, B, A, OrigA, OrigB} when B =:= OrigB, A =:= OrigA, A =/= B ->
+            S1 = move_field(B, pending_inbound, followers, A, State),
+            move_field(A, pending_outbound, following, B, S1);
+        _ -> State
+    end.
+
+%% Reject {actor: B, object: Follow{A→B}}:
+%%   drop A from B's pending_inbound
+%%   drop B from A's pending_outbound
+fold_reject(Activity, State) ->
+    case nested_follow_actor_object(Activity) of
+        {ok, B, A, OrigA, OrigB} when B =:= OrigB, A =:= OrigA, A =/= B ->
+            S1 = drop_from_field(B, pending_inbound, A, State),
+            drop_from_field(A, pending_outbound, B, S1);
+        _ -> State
+    end.
+
+%% Undo {actor: X, object: Follow{A→B}}:
+%%   Only the original Follow's actor (A) can Undo it.
+%%   Drops A↔B from every list on either side.
+fold_undo(Activity, State) ->
+    case nested_follow_actor_object(Activity) of
+        {ok, X, OrigA, OrigA, OrigB} when X =:= OrigA, OrigA =/= OrigB ->
+            S1 = drop_from_field(OrigA, following,        OrigB, State),
+            S2 = drop_from_field(OrigA, pending_outbound, OrigB, S1),
+            S3 = drop_from_field(OrigB, followers,        OrigA, S2),
+            drop_from_field(OrigB, pending_inbound, OrigA, S3);
+        _ -> State
+    end.
+
+%% ── Extraction helpers ─────────────────────────────────────────
+
+follow_actor_object(Activity) ->
+    case envelope:get_field(actor, Activity) of
+        {ok, A} ->
+            case envelope:get_field(object, Activity) of
+                {ok, B} when is_atom(B) -> {ok, A, B};
+                _ -> not_follow
+            end;
+        _ -> not_follow
+    end.
+
+%% nested_follow_actor_object/1 — pull (Actor, FollowActor, FollowObject)
+%% out of an envelope whose :object is itself a Follow proplist.
+%% Returns {ok, OuterActor, InferredPeer, InnerActor, InnerObject}.
+nested_follow_actor_object(Activity) ->
+    case envelope:get_field(actor, Activity) of
+        {ok, Outer} ->
+            case envelope:get_field(object, Activity) of
+                {ok, Inner} when is_list(Inner) ->
+                    case nested_is_follow(Inner) of
+                        true  ->
+                            case {envelope:get_field(actor, Inner),
+                                  envelope:get_field(object, Inner)} of
+                                {{ok, IA}, {ok, IO}} when is_atom(IO) ->
+                                    {ok, Outer, peer_from_inner(Outer, IA, IO), IA, IO};
+                                _ -> not_a_follow_wrapper
+                            end;
+                        false -> not_a_follow_wrapper
+                    end;
+                _ -> not_a_follow_wrapper
+            end;
+        _ -> not_a_follow_wrapper
+    end.
+
+nested_is_follow(Inner) ->
+    case envelope:get_field(type, Inner) of
+        {ok, follow} -> true;
+        _ -> false
+    end.
+
+%% peer_from_inner — for an Accept/Reject by B of Follow{A→B},
+%% Outer = B; the "peer" we move state for is A. For an Undo by A,
+%% Outer = A; the peer is B. Picking the inner actor/object that
+%% isn't Outer gives us the right pair-mate.
+peer_from_inner(Outer, IA, _IO) when Outer =:= IA -> IA;
+peer_from_inner(_Outer, IA, _IO) -> IA.
+
+%% ── Entry / field accessors ────────────────────────────────────
+
+entry_field(ActorId, Field, State) ->
+    case find_keyed(ActorId, State) of
+        {ok, Entry} ->
+            case find_keyed(Field, Entry) of
+                {ok, Val} -> Val;
+                _ -> []
+            end;
+        _ -> []
+    end.
+
+empty_entry() ->
+    [{following, []},
+     {followers, []},
+     {pending_outbound, []},
+     {pending_inbound, []}].
+
+ensure_entry(ActorId, State) ->
+    case find_keyed(ActorId, State) of
+        {ok, _} -> State;
+        _       -> State ++ [{ActorId, empty_entry()}]
+    end.
+
+add_to_field(ActorId, Field, PeerId, State) ->
+    S1 = ensure_entry(ActorId, State),
+    {ok, Entry} = find_keyed(ActorId, S1),
+    Current = entry_field(ActorId, Field, S1),
+    NewList = case contains(PeerId, Current) of
+        true  -> Current;
+        false -> Current ++ [PeerId]
+    end,
+    NewEntry = set_keyed(Field, NewList, Entry),
+    set_keyed(ActorId, NewEntry, S1).
+
+drop_from_field(ActorId, Field, PeerId, State) ->
+    case find_keyed(ActorId, State) of
+        {ok, Entry} ->
+            Current = entry_field(ActorId, Field, State),
+            NewList = remove_member(PeerId, Current),
+            NewEntry = set_keyed(Field, NewList, Entry),
+            set_keyed(ActorId, NewEntry, State);
+        _ -> State
+    end.
+
+move_field(ActorId, FromField, ToField, PeerId, State) ->
+    S1 = drop_from_field(ActorId, FromField, PeerId, State),
+    add_to_field(ActorId, ToField, PeerId, S1).
+
+%% ── List helpers ───────────────────────────────────────────────
+
+contains(_, []) -> false;
+contains(X, [X | _]) -> true;
+contains(X, [_ | Rest]) -> contains(X, Rest).
+
+remove_member(_, []) -> [];
+remove_member(X, [X | Rest]) -> remove_member(X, Rest);
+remove_member(X, [Y | Rest]) -> [Y | remove_member(X, Rest)].
+
+%% ── Keyed-list helpers ─────────────────────────────────────────
+
+find_keyed(_, []) -> {error, not_found};
+find_keyed(K, [{K, V} | _]) -> {ok, V};
+find_keyed(K, [_ | Rest]) -> find_keyed(K, Rest).
+
+set_keyed(K, V, []) -> [{K, V}];
+set_keyed(K, V, [{K, _} | Rest]) -> [{K, V} | Rest];
+set_keyed(K, V, [P | Rest]) -> [P | set_keyed(K, V, Rest)].

next/kernel/log.erl

@@ -0,0 +1,362 @@
+-module(log).
+-export([open/2, open_disk/2, open_disk/3,
+         append/2, tip/1, replay/3, entries/1,
+         segments/1]).
+
+%% Per-actor activity log — the canonical record of everything an
+%% actor has emitted, in chronological order. Per design §15.2 this
+%% lives on disk as numbered segment files; v1 started with an
+%% in-memory backend (Step 3a) so the API + seq-number machinery
+%% could be locked down before on-disk persistence (Step 3b) and
+%% segment rotation (Step 3c.a — this revision).
+%%
+%% On-disk layout:
+%%   <BasePath>/<ActorId>-NNNNNN.log
+%%
+%% NNNNNN is a 6-digit zero-padded segment index (000000..999999) so
+%% file:list_dir's alphabetical ordering coincides with numeric. Each
+%% segment file is the concat of length-prefixed frames; each frame
+%% is `<<Len:32/big>>` + `term_codec:encode(Activity)`.
+%%
+%% In-memory state (a property list):
+%%   [{actor, ActorId},
+%%    {base, BasePath},          %% binary | charlist
+%%    {seq, NextSeq},            %% next seq the log will assign
+%%    {entries, [Activity, ...]}, %% flat, append order, oldest first
+%%    {persisted, true|false},   %% does append write through?
+%%    {seg_size, MaxBytes},      %% rotate when active segment > this
+%%    {seg_lens, [N0, N1, ...]}]  %% entry count per segment in order
+%%
+%% `seg_lens` is the sole bookkeeping needed to compute (a) which
+%% segment any given seq lives in, and (b) which slice of `entries`
+%% is the active segment's contents to rewrite on append. The last
+%% element is the active segment's length.
+
+%% In-memory only — atoms accepted as BasePath for back-compat with
+%% Step 3a tests that just want the API surface.
+open(ActorId, BasePath) ->
+    {ok, [{actor, ActorId}, {base, BasePath},
+          {seq, 0}, {entries, []},
+          {persisted, false}]}.
+
+%% Disk-backed; default segment size = effectively unlimited (no
+%% rotation). Use open_disk/3 with {segment_size, N} to enable.
+open_disk(ActorId, BasePath) ->
+    open_disk(ActorId, BasePath, [{segment_size, 1073741824}]). %% 1 GiB
+
+open_disk(ActorId, BasePath, Opts) ->
+    SegSize = proplist_get(segment_size, Opts, 1073741824),
+    case load_all_segments(ActorId, BasePath) of
+        {ok, SegEntries} ->
+            %% SegEntries :: [[Entry, ...]] in segment-index order
+            %% (empty list when no segments exist on disk).
+            Lens0 = [length(S) || S <- SegEntries],
+            %% Always have at least one active segment, even if empty.
+            Lens = case Lens0 of
+                       [] -> [0];
+                       _ -> Lens0
+                   end,
+            Flat = flatten_segs(SegEntries),
+            State = [{actor, ActorId}, {base, BasePath},
+                     {seq, length(Flat)},
+                     {entries, Flat},
+                     {persisted, true},
+                     {seg_size, SegSize},
+                     {seg_lens, Lens}],
+            {ok, State};
+        {error, _} = E ->
+            E
+    end.
+
+append(LogState, Activity) ->
+    Seq = field(seq, LogState),
+    Entries = field(entries, LogState),
+    case lookup(persisted, LogState) of
+        true ->
+            SegLens = field(seg_lens, LogState),
+            SegSize = field(seg_size, LogState),
+            {NewSegLens, ActiveIdx, ActiveEntries} =
+                place_append(Entries, Activity, SegLens, SegSize),
+            Path = segment_path(field(actor, LogState),
+                                field(base, LogState),
+                                ActiveIdx),
+            ok = write_segment(Path, ActiveEntries),
+            NewState = replace_field(seq, Seq + 1,
+                       replace_field(entries, Entries ++ [Activity],
+                       replace_field(seg_lens, NewSegLens, LogState))),
+            {ok, NewState, Seq};
+        _ ->
+            NewState = replace_field(seq, Seq + 1,
+                       replace_field(entries, Entries ++ [Activity],
+                                     LogState)),
+            {ok, NewState, Seq}
+    end.
+
+tip(LogState) ->
+    field(seq, LogState).
+
+replay(LogState, InitAcc, Fun) ->
+    Entries = field(entries, LogState),
+    replay_loop(Entries, 0, InitAcc, Fun).
+
+entries(LogState) ->
+    field(entries, LogState).
+
+%% Debug accessor: returns the in-memory seg_lens (count per segment
+%% in index order). Used by rotation tests to assert that rotation
+%% happened.
+segments(LogState) ->
+    case lookup(seg_lens, LogState) of
+        undefined -> [];
+        L -> L
+    end.
+
+%% --- internals ---
+
+replay_loop([], _, Acc, _) -> Acc;
+replay_loop([Act | Rest], Seq, Acc, Fun) ->
+    replay_loop(Rest, Seq + 1, Fun(Act, Seq, Acc), Fun).
+
+%% place_append/4 decides whether the new Activity extends the current
+%% active segment or opens a fresh one, returning the resulting
+%% seg_lens, the active segment's index, and the active segment's
+%% complete entry list (the slice that needs to be (re)written to
+%% disk).
+%%
+%% Rotation rule: if the active segment already on disk is at or past
+%% the size threshold (encoded_size(OldActive) >= SegSize) AND it
+%% already holds at least one entry, the new Activity opens a new
+%% segment. A single entry larger than the threshold therefore lives
+%% on its own — we never recurse rotating a one-entry segment.
+%%
+%% This is decided BEFORE the append (looking at the pre-append size),
+%% so each segment file is written exactly once per append cycle.
+place_append(OldEntries, Activity, SegLens, SegSize) ->
+    {Pre, Last} = split_last(SegLens),
+    PreCount = sum(Pre),
+    OldActive = drop(PreCount, OldEntries),
+    OldActiveSize = encoded_size(OldActive),
+    case (OldActiveSize >= SegSize) andalso (Last >= 1) of
+        true ->
+            %% Rotate: new entry starts a brand-new segment.
+            NewSegLens = SegLens ++ [1],
+            NewActiveIdx = length(SegLens),
+            {NewSegLens, NewActiveIdx, [Activity]};
+        false ->
+            %% Stay: extend current active.
+            NewSegLens = Pre ++ [Last + 1],
+            NewActiveIdx = length(Pre),
+            {NewSegLens, NewActiveIdx, OldActive ++ [Activity]}
+    end.
+
+split_last([X]) -> {[], X};
+split_last([H | T]) ->
+    {Tl, Last} = split_last(T),
+    {[H | Tl], Last}.
+
+sum(L) -> sum_(L, 0).
+sum_([], A) -> A;
+sum_([H | T], A) -> sum_(T, A + H).
+
+drop(0, L) -> L;
+drop(_, []) -> [];
+drop(N, [_ | T]) -> drop(N - 1, T).
+
+%% flatten_segs/1 — concat a list of segments (each itself a list of
+%% entries) into a single flat list, preserving order. Used by
+%% open_disk to assemble the on-disk activity history from per-
+%% segment loads. Implemented locally because lists:append/1 isn't
+%% registered in this port — only lists:append/2.
+flatten_segs([]) -> [];
+flatten_segs([Seg | Rest]) -> Seg ++ flatten_segs(Rest).
+
+encoded_size(Entries) ->
+    byte_size(list_to_binary(
+        [frame(term_codec:encode(E)) || E <- Entries])).
+
+%% Try to read every segment file under BasePath matching the actor.
+%% Returns {ok, [[Entry, ...]]} where the outer list is in segment-
+%% index order. Empty when no segments exist.
+load_all_segments(ActorId, BasePath) ->
+    %% list_dir returns {ok, [Binary]} of entry names in sorted order
+    %% per fed-prims contract.
+    BaseChars = base_chars(BasePath),
+    case file:list_dir(BaseChars) of
+        {ok, Names} ->
+            %% Erlang string literals are NOT charlists in this port,
+            %% so build prefix/suffix as explicit char-code lists.
+            Prefix = atom_to_list(ActorId) ++ [$-],
+            Suffix = [$., $l, $o, $g],
+            Indices = collect_segment_indices(Names, Prefix, Suffix),
+            read_segments_in_order(Indices, ActorId, BasePath, []);
+        {error, enoent} ->
+            {ok, []};
+        {error, R} ->
+            {error, {read, R}}
+    end.
+
+collect_segment_indices([], _, _) -> [];
+collect_segment_indices([Name | Rest], Prefix, Suffix) ->
+    case parse_segment_name(Name, Prefix, Suffix) of
+        {ok, N} ->
+            [N | collect_segment_indices(Rest, Prefix, Suffix)];
+        not_ours ->
+            collect_segment_indices(Rest, Prefix, Suffix)
+    end.
+
+parse_segment_name(NameBin, Prefix, Suffix) when is_binary(NameBin) ->
+    parse_segment_name(binary_to_list(NameBin), Prefix, Suffix);
+parse_segment_name(Name, Prefix, Suffix) ->
+    case strip_prefix(Name, Prefix) of
+        {ok, Rest} ->
+            case strip_suffix(Rest, Suffix) of
+                {ok, NumStr} ->
+                    case is_all_digits(NumStr) of
+                        true -> {ok, list_to_integer(NumStr)};
+                        false -> not_ours
+                    end;
+                not_ours -> not_ours
+            end;
+        not_ours -> not_ours
+    end.
+
+strip_prefix(Str, []) -> {ok, Str};
+strip_prefix([C | Rest], [P | PRest]) ->
+    case C =:= P of
+        true -> strip_prefix(Rest, PRest);
+        false -> not_ours
+    end;
+strip_prefix(_, _) -> not_ours.
+
+strip_suffix(Str, Suffix) ->
+    SL = length(Str),
+    XL = length(Suffix),
+    case SL >= XL of
+        true ->
+            Head = take_n_pl(SL - XL, Str),
+            Tail = drop(SL - XL, Str),
+            case Tail =:= Suffix of
+                true -> {ok, Head};
+                false -> not_ours
+            end;
+        false -> not_ours
+    end.
+
+take_n_pl(0, _) -> [];
+take_n_pl(_, []) -> [];
+take_n_pl(N, [H | T]) -> [H | take_n_pl(N - 1, T)].
+
+is_all_digits([]) -> false;
+is_all_digits(Chars) -> all_digits(Chars).
+
+all_digits([]) -> true;
+all_digits([C | Rest]) when C >= $0, C =< $9 -> all_digits(Rest);
+all_digits(_) -> false.
+
+%% read_segments_in_order/4 — fed-prims sorts list_dir alphabetically;
+%% with 6-digit zero-padded names that coincides with numeric order.
+%% But we also accept legacy unpadded names, so sort by index to be
+%% defensive.
+read_segments_in_order(Indices, ActorId, BasePath, Acc) ->
+    Sorted = isort(Indices),
+    read_each(Sorted, ActorId, BasePath, Acc).
+
+read_each([], _, _, Acc) ->
+    {ok, lists:reverse(Acc)};
+read_each([Idx | Rest], ActorId, BasePath, Acc) ->
+    Path = segment_path(ActorId, BasePath, Idx),
+    case try_read_segment(Path) of
+        {ok, Entries} ->
+            read_each(Rest, ActorId, BasePath, [Entries | Acc]);
+        {error, _} = E -> E
+    end.
+
+%% Tiny insertion sort over a small list of integers.
+isort([]) -> [];
+isort([H | T]) -> insert(H, isort(T)).
+insert(X, []) -> [X];
+insert(X, [Y | Rest]) when X =< Y -> [X, Y | Rest];
+insert(X, [Y | Rest]) -> [Y | insert(X, Rest)].
+
+%% segment_path/3 — charlist path to the Idx'th segment file.
+segment_path(ActorId, BasePath, Idx) ->
+    base_chars(BasePath) ++ [$/] ++ atom_to_list(ActorId)
+        ++ [$-] ++ pad_int(Idx, 6) ++ [$., $l, $o, $g].
+
+base_chars(B) when is_binary(B) -> binary_to_list(B);
+base_chars(L) when is_list(L) -> L.
+
+%% Zero-pad an integer to Width digits as a charlist.
+pad_int(N, Width) ->
+    Cs = integer_to_list(N),
+    pad_left(Cs, Width).
+
+pad_left(Cs, Width) ->
+    case length(Cs) >= Width of
+        true -> Cs;
+        false -> pad_left([$0 | Cs], Width)
+    end.
+
+write_segment(Path, Entries) ->
+    Frames = [frame(term_codec:encode(E)) || E <- Entries],
+    file:write_file(Path, list_to_binary(Frames)).
+
+%% frame/1 — prepend 4-byte big-endian length to Payload.
+frame(Payload) when is_binary(Payload) ->
+    L = byte_size(Payload),
+    B3 = (L div 16777216) rem 256,
+    B2 = (L div 65536) rem 256,
+    B1 = (L div 256) rem 256,
+    B0 = L rem 256,
+    [B3, B2, B1, B0, Payload].
+
+try_read_segment(Path) ->
+    case file:read_file(Path) of
+        {ok, Bin} ->
+            try {ok, decode_frames(binary_to_list(Bin), [])}
+            catch
+                throw:Reason -> {error, {corrupt, Reason}};
+                error:Reason -> {error, {corrupt, Reason}}
+            end;
+        {error, enoent} ->
+            {ok, []};
+        {error, R} ->
+            {error, {read, R}}
+    end.
+
+decode_frames([], Acc) ->
+    lists:reverse(Acc);
+decode_frames([B3, B2, B1, B0 | Rest], Acc) ->
+    Len = B3 * 16777216 + B2 * 65536 + B1 * 256 + B0,
+    {Payload, Rest2} = take_n(Len, Rest),
+    case term_codec:decode(list_to_binary(Payload)) of
+        {ok, Term, _} -> decode_frames(Rest2, [Term | Acc]);
+        {error, R} -> throw({decode, R})
+    end;
+decode_frames(_, _) ->
+    throw(truncated_header).
+
+take_n(0, R) -> {[], R};
+take_n(N, [H | T]) ->
+    {Hs, Tl} = take_n(N - 1, T),
+    {[H | Hs], Tl};
+take_n(_, []) ->
+    throw(truncated_body).
+
+%% --- proplist helpers ---
+
+field(K, [{K, V} | _]) -> V;
+field(K, [_ | Rest]) -> field(K, Rest);
+field(_, []) -> erlang:error(badkey).
+
+lookup(K, [{K, V} | _]) -> V;
+lookup(K, [_ | Rest]) -> lookup(K, Rest);
+lookup(_, []) -> undefined.
+
+replace_field(K, V, []) -> [{K, V}];
+replace_field(K, V, [{K, _} | Rest]) -> [{K, V} | Rest];
+replace_field(K, V, [P | Rest]) -> [P | replace_field(K, V, Rest)].
+
+proplist_get(K, [{K, V} | _], _) -> V;
+proplist_get(K, [_ | Rest], Default) -> proplist_get(K, Rest, Default);
+proplist_get(_, [], Default) -> Default.

next/kernel/log_server.erl

@@ -0,0 +1,85 @@
+-module(log_server).
+-behaviour(gen_server).
+-export([start_link/2, start_link/3,
+         append/2, tip/1, entries/1, replay/3,
+         segments/1, stop/1]).
+-export([init/1, handle_call/3, handle_cast/2, handle_info/2]).
+
+%% Step 3c.b — gen_server in front of `log` that owns a single
+%% per-actor disk-backed log state and serialises concurrent
+%% appenders through `gen_server:call`.
+%%
+%% Architecture: the pure `log` module from Step 3c.a remains the
+%% canonical substrate (open_disk, append, tip, replay, entries,
+%% segments). This wrapper owns one log state per process; every
+%% public op (append/tip/entries/replay/segments) routes through
+%% gen_server:call so that the on-disk segment writer sees one
+%% append at a time, regardless of how many writer processes are
+%% pushing concurrently.
+%%
+%% Port notes carried from Step 5b's registry_server:
+%%   * `gen_server:start_link/2` returns the raw Pid, not `{ok,Pid}`.
+%%   * Spawned processes don't survive across separate
+%%     `erlang-eval-ast` invocations — every concurrency test has
+%%     to start the server, spin writers, join them, and assert all
+%%     within one eval expression.
+%%
+%% API takes the server Pid (not a registered name) so multiple
+%% per-actor servers can coexist without colliding on the registry.
+
+%% --- public API ---
+
+start_link(ActorId, BasePath) ->
+    gen_server:start_link(log_server, [ActorId, BasePath, []]).
+
+start_link(ActorId, BasePath, Opts) ->
+    gen_server:start_link(log_server, [ActorId, BasePath, Opts]).
+
+append(Pid, Activity) ->
+    gen_server:call(Pid, {append, Activity}).
+
+tip(Pid) ->
+    gen_server:call(Pid, tip).
+
+entries(Pid) ->
+    gen_server:call(Pid, entries).
+
+replay(Pid, InitAcc, Fun) ->
+    %% The fold runs server-side so the state stays consistent
+    %% with concurrent writers; the caller's Fun is closed over
+    %% the message and shipped opaque through gen_server:call.
+    gen_server:call(Pid, {replay, InitAcc, Fun}).
+
+segments(Pid) ->
+    gen_server:call(Pid, segments).
+
+stop(Pid) ->
+    gen_server:call(Pid, '$gen_stop').
+
+%% --- gen_server callbacks ---
+
+init([ActorId, BasePath, Opts]) ->
+    case Opts of
+        [] ->
+            {ok, LogState} = log:open_disk(ActorId, BasePath),
+            {ok, LogState};
+        _ ->
+            {ok, LogState} = log:open_disk(ActorId, BasePath, Opts),
+            {ok, LogState}
+    end.
+
+handle_call({append, Activity}, _From, State) ->
+    {ok, NewState, Seq} = log:append(State, Activity),
+    {reply, {ok, Seq}, NewState};
+handle_call(tip, _From, State) ->
+    {reply, log:tip(State), State};
+handle_call(entries, _From, State) ->
+    {reply, log:entries(State), State};
+handle_call({replay, InitAcc, Fun}, _From, State) ->
+    {reply, log:replay(State, InitAcc, Fun), State};
+handle_call(segments, _From, State) ->
+    {reply, log:segments(State), State}.
+
+handle_cast(_, S) -> {noreply, S}.
+
+handle_info(_, S) -> {noreply, S}.

next/kernel/nx_cid.erl

@@ -0,0 +1,24 @@
+-module(nx_cid).
+-export([from_sx/1, to_string/1, from_string/1, equals/2]).
+
+%% The kernel-side CID wrapper. The host BIF `cid:to_string/1` already
+%% produces a canonical CIDv1 (raw codec, sha2-256 multihash) over the
+%% deterministic textual form of any term (er-format-value); we expose
+%% it under the kernel namespace and add the equality + round-trip
+%% helpers the rest of the kernel needs.
+%%
+%% Naming note: the BIF module is `cid`, so we use `nx_cid` to avoid
+%% shadowing. Plans/fed-sx-milestone-1.md §Step 1 spells the file as
+%% `cid.erl`; the briefing flags Erlang snippets as illustrative.
+
+from_sx(V) ->
+    cid:to_string(V).
+
+to_string(Cid) ->
+    Cid.
+
+from_string(S) ->
+    S.
+
+equals(A, B) ->
+    A =:= B.

next/kernel/nx_kernel.erl

@@ -0,0 +1,451 @@
+-module(nx_kernel).
+-behaviour(gen_server).
+
+%% Pure-functional API
+-export([new/0, new/3,
+         add_actor/4, has_actor/2, actors/1, actor_count/1,
+         publish/2, publish/3,
+         bootstrap_actor/4,
+         actor_id/1, log_state/1, log_tip/1,
+         key_spec/1, actor_state/1, projections/1, next_published/1,
+         actor_log_state/2, actor_log_tip/2,
+         actor_inbox_state/2, actor_inbox_tip/2,
+         append_to_actor_inbox/3,
+         actor_key_spec/2, actor_state/2, actor_projections/2,
+         actor_next_published/2, actor_bucket/2,
+         with_projections/2, with_actor_projections/3,
+         next_actor_seq/1]).
+
+%% gen_server API
+-export([start_link/3, publish/1, query/0, log_tip/0,
+         with_projections/1, stop/0,
+         add_actor/3, publish_to/2, log_tip_for/1, log_state_for/1,
+         inbox_tip_for/1, inbox_state_for/1, append_inbox/2,
+         actors/0, state_for/1, bucket_for/1,
+         with_projections_for/2,
+         bootstrap_actor/3]).
+-export([init/1, handle_call/3, handle_cast/2, handle_info/2]).
+
+%% Kernel orchestrator — the long-lived runtime state held by the
+%% running fed-sx instance. Step 1 (m2) refactor: state is now
+%% per-actor bucketed so one kernel hosts any number of actors.
+%%
+%% New state shape (property list):
+%%   [{actors, [{ActorId, ActorBucket}, ...]},
+%%    {next_actor_seq, NextN}]
+%%
+%% ActorBucket = [{key_spec, KS},
+%%                {actor_state, AS},
+%%                {log, L},
+%%                {projections, [Name]},
+%%                {next_published, NextSeq}]
+%%
+%% Legacy single-actor accessors (actor_id/1, key_spec/1, etc.)
+%% continue to read from the first registered actor — keeps every
+%% pre-m2 test passing through bootstrap:start/3.
+%%
+%% next_actor_seq is a monotonic counter handed out to add_actor for
+%% future use (e.g. per-actor URL paths in Step 4). It's not yet
+%% read by the rest of the kernel.
+
+%% ── Pure-functional API ──────────────────────────────────────────
+
+new() ->
+    [{actors, []}, {next_actor_seq, 1}].
+
+new(ActorId, KeySpec, ActorStateProplist) ->
+    {ok, S} = add_actor(ActorId, KeySpec, ActorStateProplist, new()),
+    S.
+
+add_actor(ActorId, KeySpec, AS, State) ->
+    Actors = field(actors, State),
+    case has_keyed(ActorId, Actors) of
+        true ->
+            {error, already_present};
+        false ->
+            {ok, L0} = log:open(ActorId, base_stub()),
+            {ok, I0} = log:open(ActorId, inbox_base_stub()),
+            Bucket = [{key_spec, KeySpec},
+                      {actor_state, AS},
+                      {log, L0},
+                      {actor_inbox, I0},
+                      {projections, []},
+                      {next_published, 1}],
+            Seq = field(next_actor_seq, State),
+            State1 = set(actors, Actors ++ [{ActorId, Bucket}], State),
+            State2 = set(next_actor_seq, Seq + 1, State1),
+            {ok, State2}
+    end.
+
+has_actor(ActorId, State) ->
+    has_keyed(ActorId, field(actors, State)).
+
+actors(State) ->
+    [Id || {Id, _Bucket} <- field(actors, State)].
+
+actor_count(State) ->
+    length(field(actors, State)).
+
+next_actor_seq(State) ->
+    field(next_actor_seq, State).
+
+actor_bucket(ActorId, State) ->
+    find_keyed(ActorId, field(actors, State)).
+
+%% publish/3 — per-actor publish.
+publish(ActorId, Request, State) ->
+    case actor_bucket(ActorId, State) of
+        {error, no_actor} ->
+            {error, no_actor, State};
+        {ok, Bucket} ->
+            P = field(next_published, Bucket),
+            Ctx = [{actor_id,    ActorId},
+                   {published,   P},
+                   {key_spec,    field(key_spec, Bucket)},
+                   {actor_state, field(actor_state, Bucket)},
+                   {log,         field(log, Bucket)},
+                   {projections, field(projections, Bucket)}],
+            case outbox:publish(Request, Ctx) of
+                {ok, Result, NewLog} ->
+                    B1 = set(log, NewLog, Bucket),
+                    B2 = set(next_published, P + 1, B1),
+                    NewState = set_bucket(ActorId, B2, State),
+                    {ok, Result, NewState};
+                {error, Reason, _} ->
+                    {error, Reason, State}
+            end
+    end.
+
+%% publish/2 — legacy single-actor publish; routes to first actor.
+publish(Request, State) ->
+    case actors(State) of
+        [] -> {error, no_actor, State};
+        [First | _] -> publish(First, Request, State)
+    end.
+
+%% bootstrap_actor/4 — register an actor bucket and immediately
+%% publish a Create{Person|Service|Group} as that actor's first
+%% activity. Profile carries the object fields plus :public_keys.
+%% Returns {ok, Result, NewState} where Result has the published
+%% Create's CID, or {error, Reason, State} on validation halt.
+
+bootstrap_actor(ActorId, Profile, KeySpec, State) ->
+    PublicKeys = case field(public_keys, Profile) of
+        nil -> [];
+        KS  -> KS
+    end,
+    AS = [{public_keys, PublicKeys}],
+    case add_actor(ActorId, KeySpec, AS, State) of
+        {ok, State1} ->
+            ActorType = case field(type, Profile) of
+                nil -> person;
+                T   -> T
+            end,
+            Object = [{type, ActorType}] ++ collect_profile_fields(
+                [name, preferredUsername, summary, icon, public_keys],
+                Profile),
+            Request = [{type, create}, {object, Object}],
+            publish(ActorId, Request, State1);
+        {error, Reason} ->
+            {error, Reason, State}
+    end.
+
+collect_profile_fields([], _) -> [];
+collect_profile_fields([F | Rest], Profile) ->
+    case field(F, Profile) of
+        nil -> collect_profile_fields(Rest, Profile);
+        V   -> [{F, V} | collect_profile_fields(Rest, Profile)]
+    end.
+
+with_actor_projections(ActorId, Names, State) ->
+    case actor_bucket(ActorId, State) of
+        {error, no_actor} ->
+            {error, no_actor};
+        {ok, Bucket} ->
+            B1 = set(projections, Names, Bucket),
+            {ok, set_bucket(ActorId, B1, State)}
+    end.
+
+with_projections(Names, State) ->
+    case actors(State) of
+        [] -> State;
+        [First | _] ->
+            {ok, NewState} = with_actor_projections(First, Names, State),
+            NewState
+    end.
+
+%% Per-actor accessors
+
+actor_log_state(ActorId, State) ->
+    case actor_bucket(ActorId, State) of
+        {ok, B}     -> {ok, field(log, B)};
+        {error, _}  -> {error, no_actor}
+    end.
+
+actor_log_tip(ActorId, State) ->
+    case actor_log_state(ActorId, State) of
+        {ok, L}     -> log:tip(L);
+        {error, _}  -> nil
+    end.
+
+actor_inbox_state(ActorId, State) ->
+    case actor_bucket(ActorId, State) of
+        {ok, B}     -> {ok, field(actor_inbox, B)};
+        {error, _}  -> {error, no_actor}
+    end.
+
+actor_inbox_tip(ActorId, State) ->
+    case actor_inbox_state(ActorId, State) of
+        {ok, I}     -> log:tip(I);
+        {error, _}  -> nil
+    end.
+
+%% append_to_actor_inbox/3 — pure-functional inbox append. Mirrors
+%% publish/3's bucket-update shape; the activity is already signed
+%% + validated by the time it lands here (Step 5's pipeline handles
+%% sig verify + replay before this call).
+
+append_to_actor_inbox(ActorId, Activity, State) ->
+    case actor_bucket(ActorId, State) of
+        {error, no_actor} ->
+            {error, no_actor, State};
+        {ok, Bucket} ->
+            Inbox = field(actor_inbox, Bucket),
+            {ok, NewInbox, _Seq} = log:append(Inbox, Activity),
+            B1 = set(actor_inbox, NewInbox, Bucket),
+            {ok, log:tip(NewInbox), set_bucket(ActorId, B1, State)}
+    end.
+
+actor_key_spec(ActorId, State) ->
+    case actor_bucket(ActorId, State) of
+        {ok, B}     -> {ok, field(key_spec, B)};
+        {error, _}  -> {error, no_actor}
+    end.
+
+actor_state(ActorId, State) when is_list(State), is_atom(ActorId) ->
+    case actor_bucket(ActorId, State) of
+        {ok, B}     -> {ok, field(actor_state, B)};
+        {error, _}  -> {error, no_actor}
+    end.
+
+actor_projections(ActorId, State) ->
+    case actor_bucket(ActorId, State) of
+        {ok, B}     -> {ok, field(projections, B)};
+        {error, _}  -> {error, no_actor}
+    end.
+
+actor_next_published(ActorId, State) ->
+    case actor_bucket(ActorId, State) of
+        {ok, B}     -> {ok, field(next_published, B)};
+        {error, _}  -> {error, no_actor}
+    end.
+
+%% Legacy single-actor accessors — read from first bucket. Keeps
+%% every M1 test (smoke_app_pure, bootstrap_start, http_publish,
+%% nx_kernel_server, http_post_format) passing.
+
+actor_id(State) ->
+    case field(actors, State) of
+        []                        -> nil;
+        [{First, _Bucket} | _]    -> First
+    end.
+
+key_spec(State) ->
+    bucket_field(key_spec, State).
+
+actor_state(State) ->
+    bucket_field(actor_state, State).
+
+log_state(State) ->
+    bucket_field(log, State).
+
+log_tip(State) ->
+    log:tip(log_state(State)).
+
+projections(State) ->
+    case bucket_field(projections, State) of
+        nil -> [];
+        Ps  -> Ps
+    end.
+
+next_published(State) ->
+    bucket_field(next_published, State).
+
+%% ── Internal helpers ──────────────────────────────────────────────
+
+base_stub() ->
+    <<98,97,115,101,95,115,116,117,98>>.
+
+%% "inbox_base_stub" — distinct path stub so the in-memory log
+%% module's open/2 returns a fresh log state for the per-actor
+%% inbox bucket. Disk paths will namespace on this once Step 3b
+%% on-disk persistence is reactivated for inbox buckets.
+inbox_base_stub() ->
+    <<105,110,98,111,120,95,115,116,117,98>>.
+
+bucket_field(Key, State) ->
+    case field(actors, State) of
+        []                        -> nil;
+        [{_First, Bucket} | _]    -> field(Key, Bucket)
+    end.
+
+set_bucket(ActorId, NewBucket, State) ->
+    Actors = field(actors, State),
+    NewActors = set_keyed(ActorId, NewBucket, Actors),
+    set(actors, NewActors, State).
+
+set_keyed(K, V, [{K, _} | Rest]) -> [{K, V} | Rest];
+set_keyed(K, V, [P | Rest]) -> [P | set_keyed(K, V, Rest)];
+set_keyed(_, _, []) -> [].
+
+has_keyed(_, []) -> false;
+has_keyed(K, [{K, _} | _]) -> true;
+has_keyed(K, [_ | Rest]) -> has_keyed(K, Rest).
+
+find_keyed(_, []) -> {error, no_actor};
+find_keyed(K, [{K, V} | _]) -> {ok, V};
+find_keyed(K, [_ | Rest]) -> find_keyed(K, Rest).
+
+field(K, [{K, V} | _]) -> V;
+field(K, [_ | Rest]) -> field(K, Rest);
+field(_, []) -> nil.
+
+set(K, V, []) -> [{K, V}];
+set(K, V, [{K, _} | Rest]) -> [{K, V} | Rest];
+set(K, V, [P | Rest]) -> [P | set(K, V, Rest)].
+
+%% ── gen_server wrapper ──────────────────────────────────────────
+%%
+%% Mirrors the registry / projection gen_server patterns from
+%% Steps 5b and 7b. Same port quirks: raw Pid return, no `?MODULE`
+%% macro, spawned processes don't persist across separate
+%% erlang-eval-ast calls — tests inline start_link with operations.
+%%
+%% Step 1b (m2) adds multi-actor gen_server calls:
+%% add_actor/3, publish_to/2, log_tip_for/1, actors/0, state_for/1,
+%% with_projections_for/2 — all delegating to the pure-functional
+%% bucket APIs. Existing single-actor calls (publish/1, log_tip/0,
+%% with_projections/1) continue to route through bucket 0.
+
+start_link(ActorId, KeySpec, ActorStateProplist) ->
+    Pid = gen_server:start_link(nx_kernel,
+            [ActorId, KeySpec, ActorStateProplist]),
+    erlang:register(nx_kernel, Pid),
+    Pid.
+
+stop() ->
+    R = gen_server:call(nx_kernel, '$gen_stop'),
+    erlang:unregister(nx_kernel),
+    R.
+
+publish(Request) ->
+    gen_server:call(nx_kernel, {publish, Request}).
+
+query() ->
+    gen_server:call(nx_kernel, get_state).
+
+log_tip() ->
+    gen_server:call(nx_kernel, get_log_tip).
+
+with_projections(Names) ->
+    gen_server:call(nx_kernel, {set_projections, Names}).
+
+%% Step 1b — multi-actor gen_server calls.
+
+add_actor(ActorId, KeySpec, AS) ->
+    gen_server:call(nx_kernel, {add_actor, ActorId, KeySpec, AS}).
+
+publish_to(ActorId, Request) ->
+    gen_server:call(nx_kernel, {publish_to, ActorId, Request}).
+
+log_tip_for(ActorId) ->
+    gen_server:call(nx_kernel, {log_tip_for, ActorId}).
+
+log_state_for(ActorId) ->
+    gen_server:call(nx_kernel, {log_state_for, ActorId}).
+
+inbox_tip_for(ActorId) ->
+    gen_server:call(nx_kernel, {inbox_tip_for, ActorId}).
+
+inbox_state_for(ActorId) ->
+    gen_server:call(nx_kernel, {inbox_state_for, ActorId}).
+
+append_inbox(ActorId, Activity) ->
+    gen_server:call(nx_kernel, {append_inbox, ActorId, Activity}).
+
+actors() ->
+    gen_server:call(nx_kernel, get_actors).
+
+state_for(ActorId) ->
+    gen_server:call(nx_kernel, {state_for, ActorId}).
+
+bucket_for(ActorId) ->
+    gen_server:call(nx_kernel, {bucket_for, ActorId}).
+
+with_projections_for(ActorId, Names) ->
+    gen_server:call(nx_kernel, {set_projections_for, ActorId, Names}).
+
+bootstrap_actor(ActorId, Profile, KeySpec) ->
+    gen_server:call(nx_kernel, {bootstrap_actor, ActorId, Profile, KeySpec}).
+
+%% gen_server callbacks
+
+init([ActorId, KeySpec, AS]) ->
+    {ok, new(ActorId, KeySpec, AS)}.
+
+handle_call({publish, Request}, _From, State) ->
+    case publish(Request, State) of
+        {ok, Result, NewState} ->
+            {reply, {ok, Result}, NewState};
+        {error, Reason, SameState} ->
+            {reply, {error, Reason}, SameState}
+    end;
+handle_call(get_state, _From, State) ->
+    {reply, State, State};
+handle_call(get_log_tip, _From, State) ->
+    {reply, log_tip(State), State};
+handle_call({set_projections, Names}, _From, State) ->
+    {reply, ok, with_projections(Names, State)};
+handle_call({add_actor, ActorId, KeySpec, AS}, _From, State) ->
+    case add_actor(ActorId, KeySpec, AS, State) of
+        {ok, NewState}      -> {reply, ok, NewState};
+        {error, Reason}     -> {reply, {error, Reason}, State}
+    end;
+handle_call({publish_to, ActorId, Request}, _From, State) ->
+    case publish(ActorId, Request, State) of
+        {ok, Result, NewState}      -> {reply, {ok, Result}, NewState};
+        {error, Reason, SameState}  -> {reply, {error, Reason}, SameState}
+    end;
+handle_call({log_tip_for, ActorId}, _From, State) ->
+    {reply, actor_log_tip(ActorId, State), State};
+handle_call({log_state_for, ActorId}, _From, State) ->
+    {reply, actor_log_state(ActorId, State), State};
+handle_call({inbox_tip_for, ActorId}, _From, State) ->
+    {reply, actor_inbox_tip(ActorId, State), State};
+handle_call({inbox_state_for, ActorId}, _From, State) ->
+    {reply, actor_inbox_state(ActorId, State), State};
+handle_call({append_inbox, ActorId, Activity}, _From, State) ->
+    case append_to_actor_inbox(ActorId, Activity, State) of
+        {ok, Tip, NewState}     -> {reply, {ok, Tip}, NewState};
+        {error, Reason, Same}   -> {reply, {error, Reason}, Same}
+    end;
+handle_call(get_actors, _From, State) ->
+    {reply, actors(State), State};
+handle_call({state_for, ActorId}, _From, State) ->
+    {reply, actor_state(ActorId, State), State};
+handle_call({bucket_for, ActorId}, _From, State) ->
+    {reply, actor_bucket(ActorId, State), State};
+handle_call({set_projections_for, ActorId, Names}, _From, State) ->
+    case with_actor_projections(ActorId, Names, State) of
+        {ok, NewState}      -> {reply, ok, NewState};
+        {error, Reason}     -> {reply, {error, Reason}, State}
+    end;
+handle_call({bootstrap_actor, ActorId, Profile, KeySpec}, _From, State) ->
+    case bootstrap_actor(ActorId, Profile, KeySpec, State) of
+        {ok, Result, NewState}      -> {reply, {ok, Result}, NewState};
+        {error, Reason, SameState}  -> {reply, {error, Reason}, SameState}
+    end.
+
+handle_cast(_, S) -> {noreply, S}.
+
+handle_info(_, S) -> {noreply, S}.

next/kernel/outbox.erl

@@ -0,0 +1,188 @@
+-module(outbox).
+-export([construct/4, sign/2, cid_of/1, publish/2]).
+
+%% Outbox envelope construction + signing per design §3.1.
+%%
+%% construct/4 builds an unsigned activity envelope from caller-supplied
+%% (Type, ActorId, Published, Object). The envelope's `:id` field is
+%% derived from the host `cid:to_string` BIF over a skeleton tag, so
+%% recipients can address the activity by its content hash. The
+%% returned property list is the canonical key-sorted form that
+%% `envelope:canonical_bytes/1` operates on.
+%%
+%% sign/2 takes the unsigned envelope plus a KeySpec proplist that
+%% mirrors a `public_keys` entry: `[{key_id, _}, {algorithm, _},
+%% {value, KeyMaterial}]`. It computes the v1 HMAC stand-in
+%% `crypto:hash(sha256, <<KeyMaterial/binary, CanonicalBytes/binary>>)`
+%% — the same scheme `envelope:verify_signature/2` checks — and
+%% appends a `:signature` pair.
+%%
+%% Real Ed25519 / RSA signing arrives in milestone 2 once
+%% `crypto:sign_ed25519/2` BIFs land; the API shape doesn't change.
+
+%% construct/4 — Type and ActorId are atoms; Published is an
+%% integer timestamp the caller supplies (no clock BIF in this
+%% port; the HTTP layer / outbox:publish caller injects it).
+%% Object can be any term, including a property list of inner
+%% fields.
+construct(Type, ActorId, Published, Object) ->
+    Skeleton = [{actor, ActorId},
+                {object, Object},
+                {published, Published},
+                {type, Type}],
+    Id = cid:to_string({activity_envelope, Skeleton}),
+    [{actor, ActorId},
+     {id, Id},
+     {object, Object},
+     {published, Published},
+     {type, Type}].
+
+%% sign/2 — KeySpec carries key_id, algorithm, value (key material).
+sign(Envelope, KeySpec) ->
+    {ok, KeyId} = envelope:get_field(key_id, KeySpec),
+    {ok, Alg}   = envelope:get_field(algorithm, KeySpec),
+    {ok, KM}    = envelope:get_field(value, KeySpec),
+    CB = envelope:canonical_bytes(Envelope),
+    SigValue = crypto:hash(sha256, <<KM/binary, CB/binary>>),
+    Sig = [{algorithm, Alg}, {key_id, KeyId}, {value, SigValue}],
+    Envelope ++ [{signature, Sig}].
+
+%% cid_of/1 — extract the :id field from a constructed envelope.
+%% Convenience for callers that don't want to thread the CID
+%% separately when both the envelope and its ID matter.
+cid_of(Envelope) ->
+    {ok, Id} = envelope:get_field(id, Envelope),
+    Id.
+
+%% publish/2 — the outbound activity pipeline orchestrator.
+%%
+%% Request shape:   [{type, T}, {object, O}]
+%% Context shape:   [{actor_id, A}, {published, P}, {key_spec, KS},
+%%                   {actor_state, AS}, {log, L}]
+%%
+%% Returns:
+%%   {ok, [{cid, Cid}, {activity, Signed}], NewLog}   — happy path
+%%   {error, Reason, LogState}                         — validation halted
+%%
+%% Stages run in order: envelope shape, signature, replay. The
+%% replay check uses the log state pre-append, so if the caller
+%% publishes the same Request twice with the same Published
+%% timestamp the second call halts with {error, replay, _}.
+%%
+%% Projection-scheduler dispatch (the async fold the design calls
+%% for) is deferred to Step 7 — once the projection gen_server
+%% exists, this function will broadcast `Signed` to it.
+
+publish(Request, Context) ->
+    Type      = envelope_field(type, Request),
+    Object    = envelope_field(object, Request),
+    ActorId   = envelope_field(actor_id, Context),
+    Published = envelope_field(published, Context),
+    KeySpec   = envelope_field(key_spec, Context),
+    ActorState = envelope_field(actor_state, Context),
+    LogState   = envelope_field(log, Context),
+    Unsigned = construct(Type, ActorId, Published, Object),
+    Signed = sign(Unsigned, KeySpec),
+    Stages = [
+        fun (A) -> pipeline:stage_envelope(A) end,
+        pipeline:stage_signature(ActorState),
+        pipeline:stage_replay(LogState)
+    ],
+    case pipeline:run_stages(Signed, Stages) of
+        ok ->
+            {ok, NewLog, _Seq} = log:append(LogState, Signed),
+            broadcast(Signed, envelope_field(projections, Context)),
+            DeliverySet = compute_delivery_set(Request, Signed, Context),
+            dispatch_deliveries(Signed, DeliverySet, Context),
+            Result = [{cid, cid_of(Signed)},
+                      {activity, Signed},
+                      {delivery_set, DeliverySet}],
+            {ok, Result, NewLog};
+        {error, Reason} ->
+            {error, Reason, LogState}
+    end.
+
+%% dispatch_deliveries/3 — Step 8d. For each ActorId in the
+%% delivery_set, enqueue the signed activity onto the matching
+%% delivery_worker if the worker is registered under that atom.
+%% Missing workers are silently skipped — lazy creation belongs
+%% to the kernel manager (later in Step 8). The Context
+%% `:dispatch_deliveries` field gates the call so existing
+%% outbox callers that don't yet care about delivery (e.g. all of
+%% M1's tests) stay back-compat.
+%%
+%% No-op when:
+%%   - :dispatch_deliveries is absent or not the atom true
+%%   - delivery_set is []
+%%   - the per-peer worker isn't registered (whereis returns undefined)
+
+dispatch_deliveries(Activity, DeliverySet, Context) ->
+    case envelope_field(dispatch_deliveries, Context) of
+        true -> enqueue_each(Activity, DeliverySet);
+        _    -> ok
+    end.
+
+enqueue_each(_Activity, []) -> ok;
+enqueue_each(Activity, [PeerId | Rest]) when is_atom(PeerId) ->
+    case erlang:whereis(PeerId) of
+        undefined -> enqueue_each(Activity, Rest);
+        _         ->
+            delivery_worker:enqueue(PeerId, Activity),
+            enqueue_each(Activity, Rest)
+    end;
+enqueue_each(Activity, [_ | Rest]) ->
+    enqueue_each(Activity, Rest).
+
+%% compute_delivery_set/3 — Step 7c. Pulls the audience-resolved
+%% recipient list off the Request's `:to` / `:cc` fields (the
+%% envelope itself doesn't carry them — construct/4 only takes
+%% type / actor / published / object). Context's optional
+%% `:follower_graph` field carries a follower_graph state for
+%% `public` / `followers` audience expansion; absent -> empty graph,
+%% so explicit `:to` / `:cc` lists still resolve. Synthesises a
+%% recipient-shaped envelope from Request + Signed so the existing
+%% delivery:delivery_set/3 (which reads `:actor`, `:to`, `:cc`) can
+%% process it as-is.
+%%
+%% Step 8's delivery-queue worker reads `{delivery_set, [ActorId, ...]}`
+%% off the publish result and routes one HTTP POST per entry.
+
+compute_delivery_set(Request, Signed, Context) ->
+    Graph = case envelope_field(follower_graph, Context) of
+        nil -> follower_graph:new();
+        G   -> G
+    end,
+    Recipients = recipients_envelope(Request, Signed),
+    delivery:delivery_set(Recipients, [], Graph).
+
+recipients_envelope(Request, Signed) ->
+    Base = case envelope:get_field(actor, Signed) of
+        {ok, A} -> [{actor, A}];
+        _       -> []
+    end,
+    To = case envelope:get_field(to, Request) of
+        {ok, T} -> [{to, T}];
+        _       -> []
+    end,
+    Cc = case envelope:get_field(cc, Request) of
+        {ok, C} -> [{cc, C}];
+        _       -> []
+    end,
+    Base ++ To ++ Cc.
+
+%% broadcast/2 — fire-and-forget cast to each named projection.
+%% Missing/nil/empty list is a no-op; the publish API does not
+%% require projections to exist. Activity is the post-sign Signed
+%% envelope (same value that landed in the log).
+broadcast(_Activity, nil) -> ok;
+broadcast(_Activity, []) -> ok;
+broadcast(Activity, [Name | Rest]) ->
+    projection:async_fold(Name, Activity),
+    broadcast(Activity, Rest).
+
+envelope_field(K, PL) ->
+    case envelope:get_field(K, PL) of
+        {ok, V}   -> V;
+        not_found -> nil
+    end.
+

next/kernel/peer_actors.erl

@@ -0,0 +1,140 @@
+-module(peer_actors).
+-export([new/0, lookup/2, store/3, evict/2, peers/1,
+         lookup_or_fetch/3,
+         start_link/0, start_link/1, stop/0,
+         lookup_srv/1, store_srv/2, lookup_or_fetch_srv/2,
+         peers_srv/0, evict_srv/1]).
+-export([init/1, handle_call/3, handle_cast/2, handle_info/2]).
+-behaviour(gen_server).
+
+%% Peer-actors cache. On first inbound from a new peer, the
+%% federation layer needs the peer's `:public_keys` (and eventually
+%% other actor-doc fields) to verify the inbound signature. Fetching
+%% the peer's actor doc on every inbound would be wasteful, so we
+%% cache the peer-AS keyed by ActorId atom. Per design §13.6 stale-
+%% key invalidation defers to v3 — for v2 entries are TTL-free.
+%%
+%% State shape (pure-functional):
+%%   [{PeerActorId, PeerActorState}, ...]
+%%
+%% PeerActorState is the same shape that envelope:verify_signature/2
+%% reads — a proplist with :public_keys (a list of key proplists).
+%%
+%% lookup_or_fetch/3 is the load-bearing entry point: a miss invokes
+%% the caller-supplied FetchFn (1-arity, takes PeerActorId, returns
+%% {ok, PeerAS} | {error, Reason}). The cache stores successful
+%% fetches; errors do NOT poison the cache so the caller can retry.
+%%
+%% gen_server wrapper exposes the same API for the http inbox
+%% handler. Tests inline start_link with operations (same port quirks
+%% as registry / projection / nx_kernel).
+
+%% ── Pure-functional API ─────────────────────────────────────────
+
+new() -> [].
+
+lookup(PeerId, State) ->
+    case find_keyed(PeerId, State) of
+        {ok, PeerAS} -> {ok, PeerAS};
+        {error, _}   -> not_found
+    end.
+
+store(PeerId, PeerAS, State) ->
+    set_keyed(PeerId, PeerAS, State).
+
+evict(PeerId, State) ->
+    delete_keyed(PeerId, State).
+
+peers(State) -> [Id || {Id, _AS} <- State].
+
+%% lookup_or_fetch/3 — cache hit returns {ok, PeerAS, State}
+%% unchanged. Cache miss calls FetchFn; success path stores and
+%% returns {ok, PeerAS, NewState}; failure returns {error, Reason,
+%% State} so the caller knows the cache state and can retry on
+%% transient errors.
+
+lookup_or_fetch(PeerId, FetchFn, State) ->
+    case find_keyed(PeerId, State) of
+        {ok, PeerAS} -> {ok, PeerAS, State};
+        {error, _}   ->
+            case FetchFn(PeerId) of
+                {ok, PeerAS}    -> {ok, PeerAS, store(PeerId, PeerAS, State)};
+                {error, Reason} -> {error, Reason, State};
+                Other           -> {error, {bad_fetch_return, Other}, State}
+            end
+    end.
+
+%% ── gen_server wrapper ──────────────────────────────────────────
+%%
+%% Mirrors registry / projection / nx_kernel patterns. Registered
+%% name `peer_actors` so callers (http_server inbox handler) can
+%% find it without threading the Pid through Cfg.
+
+start_link() ->
+    start_link([]).
+
+start_link(InitialState) ->
+    Pid = gen_server:start_link(peer_actors, [InitialState]),
+    erlang:register(peer_actors, Pid),
+    Pid.
+
+stop() ->
+    R = gen_server:call(peer_actors, '$gen_stop'),
+    erlang:unregister(peer_actors),
+    R.
+
+lookup_srv(PeerId) ->
+    gen_server:call(peer_actors, {lookup, PeerId}).
+
+store_srv(PeerId, PeerAS) ->
+    gen_server:call(peer_actors, {store, PeerId, PeerAS}).
+
+%% lookup_or_fetch_srv/2 — same shape as the pure form. FetchFn must
+%% be a 1-arity fun. Reply is {ok, PeerAS} on hit-or-fetched,
+%% {error, Reason} on fetch failure.
+
+lookup_or_fetch_srv(PeerId, FetchFn) ->
+    gen_server:call(peer_actors, {lookup_or_fetch, PeerId, FetchFn}).
+
+peers_srv() ->
+    gen_server:call(peer_actors, get_peers).
+
+evict_srv(PeerId) ->
+    gen_server:call(peer_actors, {evict, PeerId}).
+
+%% gen_server callbacks
+
+init([InitialState]) ->
+    {ok, InitialState}.
+
+handle_call({lookup, PeerId}, _From, State) ->
+    {reply, lookup(PeerId, State), State};
+handle_call({store, PeerId, PeerAS}, _From, State) ->
+    {reply, ok, store(PeerId, PeerAS, State)};
+handle_call({lookup_or_fetch, PeerId, FetchFn}, _From, State) ->
+    case lookup_or_fetch(PeerId, FetchFn, State) of
+        {ok, PeerAS, NewState}      -> {reply, {ok, PeerAS}, NewState};
+        {error, Reason, SameState}  -> {reply, {error, Reason}, SameState}
+    end;
+handle_call(get_peers, _From, State) ->
+    {reply, peers(State), State};
+handle_call({evict, PeerId}, _From, State) ->
+    {reply, ok, evict(PeerId, State)}.
+
+handle_cast(_, S) -> {noreply, S}.
+
+handle_info(_, S) -> {noreply, S}.
+
+%% ── Internal helpers ────────────────────────────────────────────
+
+find_keyed(_, []) -> {error, not_found};
+find_keyed(K, [{K, V} | _]) -> {ok, V};
+find_keyed(K, [_ | Rest]) -> find_keyed(K, Rest).
+
+set_keyed(K, V, []) -> [{K, V}];
+set_keyed(K, V, [{K, _} | Rest]) -> [{K, V} | Rest];
+set_keyed(K, V, [P | Rest]) -> [P | set_keyed(K, V, Rest)].
+
+delete_keyed(_, []) -> [];
+delete_keyed(K, [{K, _} | Rest]) -> Rest;
+delete_keyed(K, [P | Rest]) -> [P | delete_keyed(K, Rest)].

next/kernel/pipeline.erl

@@ -0,0 +1,167 @@
+-module(pipeline).
+-export([run_stages/2,
+         validate_inbound/1, validate_inbound/3,
+         validate_outbound/1,
+         inbound_stages/0, inbound_stages/2, outbound_stages/0,
+         stage_envelope/1,
+         stage_signature/1, stage_signature/2,
+         stage_replay/1, stage_replay/2,
+         stage_schema/1, stage_schema/2]).
+
+%% Validation pipeline per design §14.
+%%
+%% A stage is a 1-arity fun `(Activity) -> ok | {error, Reason}`.
+%% The driver folds the activity through the stage list, halting
+%% on the first error. The pure-functional driver itself takes a
+%% stage list directly so tests can inject ad-hoc stage sequences
+%% without depending on the bundled inbound/outbound lists.
+%%
+%% Inbound pipeline (full set per design §14): envelope, signature,
+%% replay, audience, activity_schema, object_schema, content_validators,
+%% capabilities, trust. Outbound is a subset (no replay, no trust;
+%% auth handled at the HTTP layer).
+%%
+%% This sub-deliverable (6a) wires only the driver and the empty
+%% stage lists. Concrete stages land in 6b-6c.
+
+run_stages(_Activity, []) -> ok;
+run_stages(Activity, [Stage | Rest]) ->
+    Result = Stage(Activity),
+    case Result of
+        ok         -> run_stages(Activity, Rest);
+        {error, _} -> Result
+    end.
+
+validate_inbound(Activity) ->
+    run_stages(Activity, inbound_stages()).
+
+%% validate_inbound/3 — Step 5b federation inbound pipeline.
+%%
+%% Activity:      the signed envelope as received from the peer.
+%% PeerActorState: the peer's actor-state proplist carrying
+%%                 :public_keys for signature verification. Caller
+%%                 resolves this — for v2 it's either pre-populated
+%%                 from a peer-actors cache (Step 5c) or known from
+%%                 a two-instance test fixture.
+%% InboxLog:      the receiving actor's :actor_inbox log state.
+%%                Used by stage_replay to reject duplicate :id.
+%%
+%% Stages (per design §13.2 + §14):
+%%   stage_envelope                 — shape check
+%%   stage_signature(PeerAS)        — peer sig verify
+%%   stage_replay(InboxLog)         — replay defence against
+%%                                    receiving actor's inbox
+%%
+%% Returns ok | {error, Reason}. The driver halts on first failure.
+%% Audience / schema / capabilities / trust stages defer to v3.
+
+validate_inbound(Activity, PeerActorState, InboxLog) ->
+    run_stages(Activity, inbound_stages(PeerActorState, InboxLog)).
+
+validate_outbound(Activity) ->
+    run_stages(Activity, outbound_stages()).
+
+inbound_stages() ->
+    [fun (A) -> stage_envelope(A) end].
+
+%% inbound_stages/2 — the full ordered stage list for federation
+%% inbound (envelope -> peer sig -> replay against inbox).
+
+inbound_stages(PeerActorState, InboxLog) ->
+    [fun (A) -> stage_envelope(A) end,
+     stage_signature(PeerActorState),
+     stage_replay(InboxLog)].
+
+outbound_stages() ->
+    [fun (A) -> stage_envelope(A) end].
+
+%% ── Concrete stages ─────────────────────────────────────────────
+
+%% stage_envelope/1 — wrap envelope:validate_shape/1. The pipeline
+%% driver expects ok | {error, R}; validate_shape returns exactly
+%% that, so delegation is direct.
+stage_envelope(Activity) ->
+    envelope:validate_shape(Activity).
+
+%% stage_signature/2 — direct (Activity, ActorState) check. Wraps
+%% envelope:verify_signature/2 from Step 2c. Useful for tests and
+%% for callers that already have ActorState in scope.
+stage_signature(Activity, ActorState) ->
+    envelope:verify_signature(Activity, ActorState).
+
+%% stage_signature/1 — factory: takes the ActorState and returns a
+%% 1-arity stage fun the pipeline driver can fold. This is how
+%% signature checking gets composed into a stage list at runtime
+%% (the static `inbound_stages/0` list omits it precisely because
+%% ActorState isn't available at static-list build time).
+stage_signature(ActorState) ->
+    fun (Activity) -> envelope:verify_signature(Activity, ActorState) end.
+
+%% stage_replay/2 — checks the in-memory log for an existing
+%% activity with the same :id. Returns ok if the activity is new,
+%% `{error, replay}` if the log already carries it, `{error, no_id}`
+%% if the activity has no :id field. The check is linear scan of
+%% log entries; the projection scheduler (Step 7) will eventually
+%% maintain a CID index that turns this into O(1).
+stage_replay(Activity, LogState) ->
+    case envelope:get_field(id, Activity) of
+        not_found -> {error, no_id};
+        {ok, Id} ->
+            case log_has_id(Id, log:entries(LogState)) of
+                true  -> {error, replay};
+                false -> ok
+            end
+    end.
+
+stage_replay(LogState) ->
+    fun (Activity) -> stage_replay(Activity, LogState) end.
+
+log_has_id(_, []) -> false;
+log_has_id(Id, [Act | Rest]) ->
+    case envelope:get_field(id, Act) of
+        {ok, Id} -> true;
+        _        -> log_has_id(Id, Rest)
+    end.
+
+%% stage_schema/2 — validates the activity's :object against the
+%% schema registered for its :type. SchemaLookup is a caller-
+%% supplied fun (Type) -> {ok, SchemaFn} | not_found; SchemaFn is
+%% itself a fun (Object) -> bool. Returns:
+%%   ok                          when the schema accepts the object
+%%   {error, no_type}            when the activity has no :type
+%%   {error, schema_mismatch}    when SchemaFn returned false
+%%
+%% Open-world default: an unregistered Type returns ok so the
+%% pipeline doesn't block activities the kernel hasn't yet learned
+%% about. Tightening to strict-world happens later in milestone 2.
+%%
+%% Activities with no :object skip the schema check (some verbs
+%% legitimately carry no object).
+%%
+%% The Erlang-fun shape is the substrate-friendly stand-in for the
+%% SX-source :schema bodies stored in the genesis bundle. Once an
+%% SX-source eval bridge exists, the same stage shape will dispatch
+%% through it instead — no API change.
+stage_schema(Activity, SchemaLookup) ->
+    case envelope:get_field(type, Activity) of
+        not_found -> {error, no_type};
+        {ok, Type} ->
+            case SchemaLookup(Type) of
+                not_found -> ok;
+                {ok, SchemaFn} ->
+                    check_object_schema(Activity, SchemaFn)
+            end
+    end.
+
+check_object_schema(Activity, SchemaFn) ->
+    case envelope:get_field(object, Activity) of
+        not_found -> ok;
+        {ok, Obj} ->
+            case SchemaFn(Obj) of
+                true -> ok;
+                false -> {error, schema_mismatch}
+            end
+    end.
+
+stage_schema(SchemaLookup) ->
+    fun (Activity) -> stage_schema(Activity, SchemaLookup) end.

next/kernel/projection.erl

@@ -0,0 +1,97 @@
+-module(projection).
+-behaviour(gen_server).
+-export([new/2, new/3, fold_activity/2, replay/2,
+         name/1, state/1, fold_fn/1]).
+-export([start_link/3, async_fold/2, query/1, stop/1]).
+-export([init/1, handle_call/3, handle_cast/2, handle_info/2]).
+
+%% Pure-functional projection driver per design §10.
+%%
+%% A projection is a property list:
+%%   [{name, atom}, {state, term}, {fold, fun}]
+%%
+%% The fold function is `fun (Activity, State) -> NewState`. v1
+%% uses Erlang funs as the fold body — the genesis bundle's SX
+%% `:fold` bodies are stored as binaries; an SX-source eval
+%% bridge will plug them into the same projection record once
+%% it lands (Step 7d). For now, callers supply Erlang funs
+%% directly when constructing a projection.
+%%
+%% `replay/2` is the cold-start primitive: fold an activity
+%% list (e.g. `log:entries/1`) through the projection from its
+%% initial state.
+
+new(Name, InitialState) ->
+    new(Name, InitialState, fun (_Activity, S) -> S end).
+
+new(Name, InitialState, FoldFn) ->
+    [{name, Name}, {state, InitialState}, {fold, FoldFn}].
+
+fold_activity(Proj, Activity) ->
+    Fn  = fold_fn(Proj),
+    S0  = state(Proj),
+    S1  = Fn(Activity, S0),
+    set_field(state, S1, Proj).
+
+replay(Proj, Activities) ->
+    fold_each(Proj, Activities).
+
+fold_each(Proj, []) -> Proj;
+fold_each(Proj, [A | Rest]) ->
+    fold_each(fold_activity(Proj, A), Rest).
+
+%% Accessors
+
+name(Proj)    -> field(name, Proj).
+state(Proj)   -> field(state, Proj).
+fold_fn(Proj) -> field(fold, Proj).
+
+%% Internal
+
+field(K, [{K, V} | _]) -> V;
+field(K, [_ | Rest]) -> field(K, Rest);
+field(_, []) -> erlang:error(badkey).
+
+set_field(K, V, [{K, _} | Rest]) -> [{K, V} | Rest];
+set_field(K, V, [P | Rest]) -> [P | set_field(K, V, Rest)];
+set_field(K, V, []) -> [{K, V}].
+
+%% ── Step 7b: gen_server wrapper ─────────────────────────────────
+%%
+%% Each projection runs in its own gen_server, registered under the
+%% projection's Name atom. `async_fold/2` casts an activity into the
+%% process; `query/1` synchronously fetches the current state.
+%%
+%% Port notes (mirroring Step 5b on the registry): `gen_server:start_link`
+%% returns the raw Pid; `?MODULE` macro is unsupported; spawned
+%% processes don't survive across separate `erlang-eval-ast` calls
+%% so tests must inline start_link with their operations.
+
+start_link(Name, InitialState, FoldFn) ->
+    Pid = gen_server:start_link(projection, [Name, InitialState, FoldFn]),
+    erlang:register(Name, Pid),
+    Pid.
+
+async_fold(Name, Activity) ->
+    gen_server:cast(Name, {fold, Activity}).
+
+query(Name) ->
+    gen_server:call(Name, get_state).
+
+stop(Name) ->
+    R = gen_server:call(Name, '$gen_stop'),
+    erlang:unregister(Name),
+    R.
+
+%% gen_server callbacks
+
+init([Name, InitialState, FoldFn]) ->
+    {ok, new(Name, InitialState, FoldFn)}.
+
+handle_call(get_state, _From, Proj) ->
+    {reply, state(Proj), Proj}.
+
+handle_cast({fold, Activity}, Proj) ->
+    {noreply, fold_activity(Proj, Activity)}.
+
+handle_info(_, Proj) -> {noreply, Proj}.

next/kernel/registry.erl

@@ -0,0 +1,120 @@
+-module(registry).
+-behaviour(gen_server).
+-export([new/0, kinds/0, register/4, lookup/3, list/2]).
+-export([start_link/0, register/3, lookup/2, list/1, stop/0]).
+-export([init/1, handle_call/3, handle_cast/2, handle_info/2]).
+
+%% Pure-functional registry for the seven bootstrap kinds.
+%%
+%% State is a property list keyed by kind atom; each kind's value
+%% is itself a property list of {Name, Entry} pairs. Entry is
+%% opaque — typically a proplist with :cid, :schema, :semantics,
+%% :supersedes fields, but the registry doesn't enforce that here.
+%%
+%% A gen_server wrapper (Step 5b) will own the global registry
+%% process; the pure functions in this module remain the canonical
+%% API and are usable for tests and for offline projection-replay.
+%%
+%% Return shapes:
+%%   new/0            -> State
+%%   kinds/0          -> [Atom, ...]
+%%   register/4       -> {ok, NewState} | {error, unknown_kind}
+%%   lookup/3         -> {ok, Entry} | not_found | {error, unknown_kind}
+%%   list/2           -> [{Name, Entry}, ...] | {error, unknown_kind}
+
+new() -> [].
+
+kinds() ->
+    [activity_types, object_types, projections,
+     validators, codecs, sig_suites, audience].
+
+register(Kind, Name, Entry, State) ->
+    case is_valid_kind(Kind) of
+        false -> {error, unknown_kind};
+        true ->
+            Entries = kind_entries(Kind, State),
+            Updated = put_pair(Name, Entry, Entries),
+            {ok, set_kind_entries(Kind, Updated, State)}
+    end.
+
+lookup(Kind, Name, State) ->
+    case is_valid_kind(Kind) of
+        false -> {error, unknown_kind};
+        true ->
+            find_pair(Name, kind_entries(Kind, State))
+    end.
+
+list(Kind, State) ->
+    case is_valid_kind(Kind) of
+        false -> {error, unknown_kind};
+        true  -> kind_entries(Kind, State)
+    end.
+
+%% ── Internal ────────────────────────────────────────────────────
+
+is_valid_kind(K) -> lists:member(K, kinds()).
+
+kind_entries(Kind, State) ->
+    case find_pair(Kind, State) of
+        not_found -> [];
+        {ok, V}   -> V
+    end.
+
+set_kind_entries(Kind, Entries, State) ->
+    put_pair(Kind, Entries, State).
+
+put_pair(K, V, []) -> [{K, V}];
+put_pair(K, V, [{K, _} | Rest]) -> [{K, V} | Rest];
+put_pair(K, V, [P | Rest]) -> [P | put_pair(K, V, Rest)].
+
+find_pair(_, []) -> not_found;
+find_pair(K, [{K, V} | _]) -> {ok, V};
+find_pair(K, [_ | Rest]) -> find_pair(K, Rest).
+
+%% ── Step 5b: gen_server wrapper ─────────────────────────────────
+%%
+%% The named process owns the registry state; concurrent readers
+%% and writers serialize through gen_server:call. The pure /3 and
+%% /4 functions remain available for offline projection-replay and
+%% for tests that don't need a process at all.
+%%
+%% Port notes: gen_server:start_link returns the raw Pid (not
+%% `{ok, Pid}` as in OTP). `?MODULE` macro is unsupported here, so
+%% the registered name is the literal `registry` atom in every call.
+
+start_link() ->
+    Pid = gen_server:start_link(registry, []),
+    erlang:register(registry, Pid),
+    Pid.
+
+stop() ->
+    R = gen_server:call(registry, '$gen_stop'),
+    erlang:unregister(registry),
+    R.
+
+register(Kind, Name, Entry) ->
+    gen_server:call(registry, {register, Kind, Name, Entry}).
+
+lookup(Kind, Name) ->
+    gen_server:call(registry, {lookup, Kind, Name}).
+
+list(Kind) ->
+    gen_server:call(registry, {list, Kind}).
+
+%% gen_server callbacks
+
+init(_) -> {ok, new()}.
+
+handle_call({register, Kind, Name, Entry}, _From, State) ->
+    case register(Kind, Name, Entry, State) of
+        {ok, NewState} -> {reply, ok, NewState};
+        {error, R}     -> {reply, {error, R}, State}
+    end;
+handle_call({lookup, Kind, Name}, _From, State) ->
+    {reply, lookup(Kind, Name, State), State};
+handle_call({list, Kind}, _From, State) ->
+    {reply, list(Kind, State), State}.
+
+handle_cast(_, S) -> {noreply, S}.
+
+handle_info(_, S) -> {noreply, S}.

next/kernel/sandbox.erl

@@ -0,0 +1,41 @@
+-module(sandbox).
+-export([eval_pure/2, eval_pure/3]).
+
+%% Sandboxed evaluation of an Erlang fun.
+%%
+%% eval_pure/2(Fun, Arg)            -> {ok, Result} | {error, Reason}
+%% eval_pure/3(Fun, Arg1, Arg2)     -> {ok, Result} | {error, Reason}
+%%
+%% The 3-arity variant matches the (Activity, State) -> NewState
+%% shape of projection folds. The projection scheduler can wrap
+%% every fold call in `sandbox:eval_pure(Fun, Act, State)` to
+%% ensure a misbehaving fold body can't crash the projection
+%% gen_server.
+%%
+%% v1 sandboxing is just the try/catch envelope: no gas budget,
+%% no IO denial, no environment stripping. Real sandboxing lands
+%% with SX-source eval (the fold body would then be an SX form
+%% evaluated under the spec/harness platform). The API shape is
+%% stable — callers don't need to change when that arrives.
+
+%% Port note: this Erlang implementation catches by explicit
+%% class names (throw, error, exit) rather than the open
+%% `Class:Reason` pattern. The wrappers below enumerate the three.
+
+eval_pure(Fun, Arg) ->
+    try Fun(Arg) of
+        Result -> {ok, Result}
+    catch
+        throw:Reason -> {error, {throw, Reason}};
+        error:Reason -> {error, {error, Reason}};
+        exit:Reason  -> {error, {exit, Reason}}
+    end.
+
+eval_pure(Fun, Arg1, Arg2) ->
+    try Fun(Arg1, Arg2) of
+        Result -> {ok, Result}
+    catch
+        throw:Reason -> {error, {throw, Reason}};
+        error:Reason -> {error, {error, Reason}};
+        exit:Reason  -> {error, {exit, Reason}}
+    end.

next/kernel/term_codec.erl

@@ -0,0 +1,105 @@
+-module(term_codec).
+-export([encode/1, decode/1]).
+
+%% Erlang-side term <-> binary codec, built on the substrate fixes from
+%% commits 24e3bf53 (binary_to_list / list_to_binary), 3d80bd8c ($X char
+%% literals), 4852cca9 (atom_to_list / integer_to_list charlists).
+%%
+%% Wire format (netstring-ish; all length headers ASCII decimal):
+%%
+%%   atom        $a Len $: NameBytes
+%%   integer     $i Len $: DecimalBytes   (negative ints carry leading $-)
+%%   binary      $b Len $: RawBytes
+%%   tuple       $t Count $: Enc1 Enc2 ... Encn
+%%   list        $l Count $: Enc1 Enc2 ... Encn      (proper list)
+%%   nil         $l $0 $:                            (empty list)
+%%
+%% Each Enc is itself one of these forms — recursive. The format is
+%% byte-clean: binary bodies may contain any byte (newlines, NULs, etc.),
+%% so callers can frame entries with a 4-byte big-endian length prefix
+%% (Step 3b on-disk segment writer's job).
+
+%% encode/1: term -> binary
+encode(T) when is_atom(T) ->
+    Cs = atom_to_list(T),
+    list_to_binary([$a, integer_to_list(length(Cs)), $:, Cs]);
+encode(T) when is_integer(T) ->
+    Cs = integer_to_list(T),
+    list_to_binary([$i, integer_to_list(length(Cs)), $:, Cs]);
+encode(T) when is_binary(T) ->
+    list_to_binary([$b, integer_to_list(byte_size(T)), $:, T]);
+encode(T) when is_tuple(T) ->
+    L = tuple_to_list(T),
+    list_to_binary([$t, integer_to_list(length(L)), $:,
+                    [encode(E) || E <- L]]);
+encode([]) ->
+    list_to_binary([$l, $0, $:]);
+encode(T) when is_list(T) ->
+    list_to_binary([$l, integer_to_list(length(T)), $:,
+                    [encode(E) || E <- T]]).
+
+%% decode/1: binary -> {ok, Term, RestBinary} | {error, badform}
+%% On success returns the remaining unconsumed bytes so callers can
+%% stream-decode multiple frames from one buffer.
+decode(B) when is_binary(B) ->
+    decode_chars(binary_to_list(B)).
+
+decode_chars([$a | Rest]) ->
+    {Len, Rest1} = read_len(Rest, 0),
+    Rest2 = strip_colon(Rest1),
+    {NameChars, Rest3} = split_at(Len, Rest2),
+    {ok, list_to_atom(NameChars), list_to_binary(Rest3)};
+decode_chars([$i | Rest]) ->
+    {Len, Rest1} = read_len(Rest, 0),
+    Rest2 = strip_colon(Rest1),
+    {NumChars, Rest3} = split_at(Len, Rest2),
+    {ok, list_to_integer(NumChars), list_to_binary(Rest3)};
+decode_chars([$b | Rest]) ->
+    {Len, Rest1} = read_len(Rest, 0),
+    Rest2 = strip_colon(Rest1),
+    {Bytes, Rest3} = split_at(Len, Rest2),
+    {ok, list_to_binary(Bytes), list_to_binary(Rest3)};
+decode_chars([$t | Rest]) ->
+    {N, Rest1} = read_len(Rest, 0),
+    Rest2 = strip_colon(Rest1),
+    {Elems, Rest3} = decode_n(N, Rest2, []),
+    {ok, list_to_tuple(Elems), list_to_binary(Rest3)};
+decode_chars([$l | Rest]) ->
+    {N, Rest1} = read_len(Rest, 0),
+    Rest2 = strip_colon(Rest1),
+    {Elems, Rest3} = decode_n(N, Rest2, []),
+    {ok, Elems, list_to_binary(Rest3)};
+decode_chars(_) ->
+    {error, badform}.
+
+read_len([C | Rest], Acc) when C >= $0, C =< $9 ->
+    read_len(Rest, Acc * 10 + C - $0);
+read_len([$- | Rest], 0) ->
+    %% Leading minus for negative integer-body lengths is invalid for
+    %% lengths, but appears inside integer-body bytes (handled in
+    %% the body, not here — read_len only consumes digits before $:).
+    {0, [$- | Rest]};
+read_len(Rest, Acc) ->
+    {Acc, Rest}.
+
+strip_colon([$: | Rest]) -> Rest;
+strip_colon(Other) -> erlang:error({badform, Other}).
+
+split_at(0, Rest) -> {[], Rest};
+split_at(N, [H | T]) ->
+    {Hs, Tl} = split_at(N - 1, T),
+    {[H | Hs], Tl};
+split_at(_, []) ->
+    erlang:error({badform, short}).
+
+decode_n(0, Rest, Acc) ->
+    {lists:reverse(Acc), Rest};
+decode_n(N, Bytes, Acc) ->
+    {Term, Rest} = decode_one(Bytes),
+    decode_n(N - 1, Rest, [Term | Acc]).
+
+decode_one(Bytes) ->
+    case decode_chars(Bytes) of
+        {ok, Term, RestBin} -> {Term, binary_to_list(RestBin)};
+        {error, R} -> erlang:error({badform, R})
+    end.

next/tests/actor_lifecycle.sh

@@ -0,0 +1,164 @@
+#!/usr/bin/env bash
+# next/tests/actor_lifecycle.sh — m2 Step 2c end-to-end test.
+#
+# Ties Step 2a artefacts (genesis Person/Service/Group SX files),
+# Step 2b projection (actor_state.erl), and Step 2c bootstrap
+# (nx_kernel:bootstrap_actor/4) together. Profiles bootstrap as
+# Create{Person|Service|Group} activities; the actor_state projection
+# folds them into the per-actor profile registry.
+
+set -uo pipefail
+cd "$(git rev-parse --show-toplevel)"
+
+SX_SERVER="${SX_SERVER:-hosts/ocaml/_build/default/bin/sx_server.exe}"
+if [ ! -x "$SX_SERVER" ]; then
+  SX_SERVER="/root/rose-ash/hosts/ocaml/_build/default/bin/sx_server.exe"
+fi
+if [ ! -x "$SX_SERVER" ]; then
+  echo "ERROR: sx_server.exe not found." >&2
+  exit 1
+fi
+
+VERBOSE="${1:-}"
+PASS=0; FAIL=0; ERRORS=""
+TMPFILE=$(mktemp); trap "rm -f $TMPFILE" EXIT
+
+# Two actors share signing-key bytes (each in its own AS). The
+# profile's :public_keys list is what gets wrapped in the Create
+# object; the kernel-side AS proplist (built by bootstrap_actor/4
+# from :public_keys) is what envelope:verify_signature reads.
+ALICE_KM='AliceK = <<1,2,3,4>>, AliceKey = [{id, k1}, {created, 0}, {value, AliceK}], AlicePks = [AliceKey], AliceKS = [{key_id, k1}, {algorithm, ed25519}, {value, AliceK}],'
+BOB_KM='BobK = <<5,6,7,8>>, BobKey = [{id, k1}, {created, 0}, {value, BobK}], BobPks = [BobKey], BobKS = [{key_id, k1}, {algorithm, ed25519}, {value, BobK}],'
+ALICE_PROFILE='AliceProfile = [{type, person}, {name, alice_n}, {preferredUsername, alice_local}, {public_keys, AlicePks}],'
+BOB_PROFILE='BobProfile = [{type, service}, {name, bobbot_n}, {preferredUsername, bobbot_local}, {public_keys, BobPks}],'
+
+# actor_state projection wiring — fold_fn from actor_state:fold_fn/0,
+# initial state = actor_state:new().
+PROJ_SETUP='projection:start_link(actors, actor_state:new(), actor_state:fold_fn()),'
+
+cat > "$TMPFILE" <<EPOCHS
+(epoch 1)
+(load "lib/erlang/tokenizer.sx")
+(load "lib/erlang/parser.sx")
+(load "lib/erlang/parser-core.sx")
+(load "lib/erlang/parser-expr.sx")
+(load "lib/erlang/parser-module.sx")
+(load "lib/erlang/transpile.sx")
+(load "lib/erlang/runtime.sx")
+(load "lib/erlang/vm/dispatcher.sx")
+(epoch 2)
+(eval "(er-load-gen-server!)")
+(epoch 3)
+(eval "(get (erlang-load-module (file-read \"next/kernel/envelope.erl\")) :name)")
+(epoch 4)
+(eval "(get (erlang-load-module (file-read \"next/kernel/log.erl\")) :name)")
+(epoch 5)
+(eval "(get (erlang-load-module (file-read \"next/kernel/pipeline.erl\")) :name)")
+(epoch 6)
+(eval "(get (erlang-load-module (file-read \"next/kernel/outbox.erl\")) :name)")
+(epoch 7)
+(eval "(get (erlang-load-module (file-read \"next/kernel/projection.erl\")) :name)")
+(epoch 8)
+(eval "(get (erlang-load-module (file-read \"next/kernel/actor_state.erl\")) :name)")
+(epoch 9)
+(eval "(get (erlang-load-module (file-read \"next/kernel/nx_kernel.erl\")) :name)")
+
+;; Pure: bootstrap_actor/4 on a fresh kernel publishes Create and
+;; returns {ok, Result, S}.
+(epoch 10)
+(eval "(get (erlang-eval-ast \"${ALICE_KM} ${BOB_KM} ${ALICE_PROFILE} ${BOB_PROFILE} case nx_kernel:bootstrap_actor(alice, AliceProfile, AliceKS, nx_kernel:new()) of {ok, _, _} -> ok; _ -> bad end\") :name)")
+
+;; Pure: after bootstrap, log_tip = 1, has_actor true
+(epoch 11)
+(eval "(get (erlang-eval-ast \"${ALICE_KM} ${BOB_KM} ${ALICE_PROFILE} ${BOB_PROFILE} {ok, _, S} = nx_kernel:bootstrap_actor(alice, AliceProfile, AliceKS, nx_kernel:new()), nx_kernel:has_actor(alice, S) andalso nx_kernel:actor_log_tip(alice, S) =:= 1\") :name)")
+
+;; Pure: log entry is a Create with object's type = person
+(epoch 12)
+(eval "(get (erlang-eval-ast \"${ALICE_KM} ${BOB_KM} ${ALICE_PROFILE} ${BOB_PROFILE} {ok, _, S} = nx_kernel:bootstrap_actor(alice, AliceProfile, AliceKS, nx_kernel:new()), {ok, L} = nx_kernel:actor_log_state(alice, S), [E] = log:entries(L), {ok, create} = envelope:get_field(type, E), {ok, Obj} = envelope:get_field(object, E), envelope:get_field(type, Obj) =:= {ok, person}\") :name)")
+
+;; Pure: bootstrap into existing kernel with another actor
+(epoch 13)
+(eval "(get (erlang-eval-ast \"${ALICE_KM} ${BOB_KM} ${ALICE_PROFILE} ${BOB_PROFILE} {ok, _, S1} = nx_kernel:bootstrap_actor(alice, AliceProfile, AliceKS, nx_kernel:new()), {ok, _, S2} = nx_kernel:bootstrap_actor(bobbot, BobProfile, BobKS, S1), nx_kernel:actors(S2) =:= [alice, bobbot]\") :name)")
+
+;; Pure: two actors have independent log_tips
+(epoch 14)
+(eval "(get (erlang-eval-ast \"${ALICE_KM} ${BOB_KM} ${ALICE_PROFILE} ${BOB_PROFILE} {ok, _, S1} = nx_kernel:bootstrap_actor(alice, AliceProfile, AliceKS, nx_kernel:new()), {ok, _, S2} = nx_kernel:bootstrap_actor(bobbot, BobProfile, BobKS, S1), {nx_kernel:actor_log_tip(alice, S2), nx_kernel:actor_log_tip(bobbot, S2)} =:= {1, 1}\") :name)")
+
+;; Pure: duplicate bootstrap_actor returns already_present
+(epoch 15)
+(eval "(get (erlang-eval-ast \"${ALICE_KM} ${BOB_KM} ${ALICE_PROFILE} ${BOB_PROFILE} {ok, _, S1} = nx_kernel:bootstrap_actor(alice, AliceProfile, AliceKS, nx_kernel:new()), case nx_kernel:bootstrap_actor(alice, AliceProfile, AliceKS, S1) of {error, already_present, _} -> ok; _ -> bad end\") :name)")
+
+;; gen_server: bootstrap_actor/3 publishes + actor_state projection captures profile
+(epoch 16)
+(eval "(get (erlang-eval-ast \"${ALICE_KM} ${BOB_KM} ${ALICE_PROFILE} ${BOB_PROFILE} nx_kernel:start_link(seed, AliceKS, [{public_keys, AlicePks}]), ${PROJ_SETUP} nx_kernel:with_projections_for(seed, [actors]), {ok, _} = nx_kernel:bootstrap_actor(alice, AliceProfile, AliceKS), nx_kernel:has_actor(seed, nx_kernel:query()) andalso nx_kernel:has_actor(alice, nx_kernel:query())\") :name)")
+
+;; gen_server: actor_state projection captures the bootstrapped Person profile
+(epoch 17)
+(eval "(get (erlang-eval-ast \"${ALICE_KM} ${BOB_KM} ${ALICE_PROFILE} ${BOB_PROFILE} nx_kernel:start_link(seed, AliceKS, [{public_keys, AlicePks}]), ${PROJ_SETUP} nx_kernel:with_projections_for(alice_pre, [actors]), nx_kernel:add_actor(alice_pre, AliceKS, [{public_keys, AlicePks}]), nx_kernel:with_projections_for(alice_pre, [actors]), {ok, _} = nx_kernel:publish_to(alice_pre, [{type, create}, {object, [{type, person}, {name, alice_n}, {preferredUsername, alice_local}, {public_keys, AlicePks}]}]), {ok, Profile} = actor_state:lookup(alice_pre, projection:query(actors)), actor_state:profile_type(Profile) =:= person andalso actor_state:profile_name(Profile) =:= alice_n\") :name)")
+
+;; gen_server: Service profile lands as service in actor_state
+(epoch 18)
+(eval "(get (erlang-eval-ast \"${ALICE_KM} ${BOB_KM} ${ALICE_PROFILE} ${BOB_PROFILE} nx_kernel:start_link(seed, BobKS, [{public_keys, BobPks}]), ${PROJ_SETUP} nx_kernel:add_actor(bobbot, BobKS, [{public_keys, BobPks}]), nx_kernel:with_projections_for(bobbot, [actors]), {ok, _} = nx_kernel:publish_to(bobbot, [{type, create}, {object, [{type, service}, {name, bobbot_n}, {public_keys, BobPks}]}]), {ok, Profile} = actor_state:lookup(bobbot, projection:query(actors)), actor_state:profile_type(Profile) =:= service\") :name)")
+
+;; gen_server: Group profile lands as group in actor_state
+(epoch 19)
+(eval "(get (erlang-eval-ast \"${ALICE_KM} nx_kernel:start_link(seed, AliceKS, [{public_keys, AlicePks}]), ${PROJ_SETUP} nx_kernel:add_actor(wg1, AliceKS, [{public_keys, AlicePks}]), nx_kernel:with_projections_for(wg1, [actors]), {ok, _} = nx_kernel:publish_to(wg1, [{type, create}, {object, [{type, group}, {name, working_group_n}, {public_keys, AlicePks}]}]), {ok, Profile} = actor_state:lookup(wg1, projection:query(actors)), actor_state:profile_type(Profile) =:= group\") :name)")
+
+;; Sanity: profile captures :preferredUsername + :public_keys from the Create object
+(epoch 20)
+(eval "(get (erlang-eval-ast \"${ALICE_KM} ${BOB_KM} ${ALICE_PROFILE} ${BOB_PROFILE} nx_kernel:start_link(seed, AliceKS, [{public_keys, AlicePks}]), ${PROJ_SETUP} nx_kernel:add_actor(alice, AliceKS, [{public_keys, AlicePks}]), nx_kernel:with_projections_for(alice, [actors]), {ok, _} = nx_kernel:publish_to(alice, [{type, create}, {object, [{type, person}, {name, alice_n}, {preferredUsername, alice_local}, {public_keys, AlicePks}]}]), {ok, Profile} = actor_state:lookup(alice, projection:query(actors)), actor_state:profile_field(preferredUsername, Profile) =:= {ok, alice_local} andalso actor_state:profile_field(public_keys, Profile) =:= {ok, AlicePks}\") :name)")
+
+;; Pure: profile defaults to person when :type missing
+(epoch 21)
+(eval "(get (erlang-eval-ast \"${ALICE_KM} TypelessProfile = [{name, alice_n}, {public_keys, AlicePks}], {ok, _, S} = nx_kernel:bootstrap_actor(alice, TypelessProfile, AliceKS, nx_kernel:new()), {ok, L} = nx_kernel:actor_log_state(alice, S), [E] = log:entries(L), {ok, Obj} = envelope:get_field(object, E), envelope:get_field(type, Obj) =:= {ok, person}\") :name)")
+
+;; Pure: empty profile :public_keys defaults to []
+(epoch 22)
+(eval "(get (erlang-eval-ast \"${ALICE_KM} EmptyProfile = [{type, person}, {name, alice_n}], case nx_kernel:bootstrap_actor(alice, EmptyProfile, AliceKS, nx_kernel:new()) of {ok, _, _} -> ok; {error, _, _} -> ok end\") :name)")
+EPOCHS
+
+OUTPUT=$(timeout 240 "$SX_SERVER" < "$TMPFILE" 2>/dev/null)
+
+check() {
+  local epoch="$1" desc="$2" expected="$3"
+  local actual
+  actual=$(echo "$OUTPUT" | awk -v e="$epoch" '
+    $0 ~ "^\\(ok-len " e " " { getline; print; exit }
+    $0 ~ "^\\(ok " e " "     { print; exit }
+    $0 ~ "^\\(error " e " "  { print; exit }
+  ')
+  [ -z "$actual" ] && actual="<no output for epoch $epoch>"
+  if echo "$actual" | grep -qF -- "$expected"; then
+    PASS=$((PASS+1))
+    [ "$VERBOSE" = "-v" ] && echo "  ok $desc"
+  else
+    FAIL=$((FAIL+1))
+    ERRORS+="  FAIL [$desc] (epoch $epoch) expected: $expected | actual: $actual
+"
+  fi
+}
+
+check  2  "gen_server loaded"                "gen_server"
+check  9  "nx_kernel loaded"                  "nx_kernel"
+check 10  "bootstrap_actor/4 -> {ok, _, _}"   "ok"
+check 11  "bootstrap_actor advances log_tip"  "true"
+check 12  "log entry is Create{Person}"       "true"
+check 13  "two actors live in one kernel"     "true"
+check 14  "independent log_tips after boot"   "true"
+check 15  "duplicate boot -> already_present" "ok"
+check 16  "gen_server bootstrap_actor/3"      "true"
+check 17  "actor_state captures Person"       "true"
+check 18  "actor_state captures Service"      "true"
+check 19  "actor_state captures Group"        "true"
+check 20  "profile carries preferredUsername" "true"
+check 21  "typeless profile defaults Person"  "true"
+check 22  "empty public_keys handled"         "ok"
+
+TOTAL=$((PASS+FAIL))
+if [ $FAIL -eq 0 ]; then
+  echo "ok $PASS/$TOTAL next/tests/actor_lifecycle.sh passed"
+else
+  echo "FAIL $PASS/$TOTAL passed, $FAIL failed:"
+  echo "$ERRORS"
+fi
+[ $FAIL -eq 0 ]