fed-sx-m2: Step 2b — actor_state projection fold + 19 tests

next/kernel/actor_state.erl mirrors define_registry's structure: a
2-arity fold_fn that plugs into projection:start_link/3, an
Erlang-fun stand-in for the genesis actor-state.sx projection body.

State shape:
  [{ActorId, Profile}, ...]

Profile is a property list with :type, :name, :preferredUsername,
:summary, :icon, :public_keys, :moved_to, :created. Maps #{} aren't
registered in this substrate, so this matches the kernel bucket /
registry shape convention.

Folding rules per design §9.1-§9.4:
  - Create{Person|Service|Group}: register profile, capturing object
    fields + :published seq as :created. Duplicate Create no-overwrite.
  - Update{Person|Service|Group, patch}: deep-merge :patch into
    profile last-write-wins per key.
  - Move: record :moved_to.
Other activity types and non-actor object Creates pass through.

Local find_keyed/has_keyed/set_keyed helpers (same gap as Step 1a:
no lists:keyfind/keymember in this substrate).

19/19 in next/tests/actor_state_pure.sh covering:
  - new/0/has/2/lookup/2/actors/1 base cases
  - Create for Person/Service/Group all three actor types
  - Profile field capture (name, preferredUsername, public_keys, created)
  - Duplicate Create no-overwrite
  - Two independent actors
  - Update field merge + per-key last-write-wins
  - Update for unknown actor pass-through
  - Move :moved_to
  - Non-actor Creates pass through
  - Activities without :actor pass through
  - fold_fn/0 returns is_function(F, 2)

Conformance 761/761. Step-2-adjacent no-regression gate 106/106
across 6 suites (define_registry_pure, projection_pure,
projection_server, nx_kernel_multi, bootstrap_start, smoke_app_pure).

next/kernel/actor_state.erl

@@ -0,0 +1,178 @@
+-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]).
+
+%% 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} ->
+                            NewProfile = merge_patch(Profile, Patch),
+                            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.
+
+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/tests/actor_state_pure.sh

@@ -0,0 +1,163 @@
+#!/usr/bin/env bash
+# next/tests/actor_state_pure.sh — m2 Step 2b test.
+#
+# Exercises the Erlang-fun stand-in for the actor-state projection
+# fold. Activities flow:
+#   Create{Person|Service|Group} -> profile registered
+#   Update{Person|Service|Group, patch} -> patch deep-merged
+#   Move -> :moved_to recorded
+# Non-actor object Creates pass through.
+
+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 $TMPFILE" EXIT
+
+cat > "$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 "(get (erlang-load-module (file-read \"next/kernel/envelope.erl\")) :name)")
+(epoch 3)
+(eval "(get (erlang-load-module (file-read \"next/kernel/actor_state.erl\")) :name)")
+
+;; new/0 returns []
+(epoch 10)
+(eval "(get (erlang-eval-ast \"actor_state:new() =:= []\") :name)")
+
+;; has/2 false on empty
+(epoch 11)
+(eval "(get (erlang-eval-ast \"actor_state:has(alice, actor_state:new()) =:= false\") :name)")
+
+;; lookup/2 not_found on empty
+(epoch 12)
+(eval "(get (erlang-eval-ast \"actor_state:lookup(alice, actor_state:new()) =:= not_found\") :name)")
+
+;; actors/1 returns [] on empty
+(epoch 13)
+(eval "(get (erlang-eval-ast \"actor_state:actors(actor_state:new()) =:= []\") :name)")
+
+;; Create{Person} registers profile
+(epoch 14)
+(eval "(get (erlang-eval-ast \"Obj = [{type, person}, {name, alice_name}, {preferredUsername, alice_local}], Act = [{actor, alice}, {type, create}, {object, Obj}, {published, 1}], S = actor_state:fold(Act, actor_state:new()), actor_state:has(alice, S)\") :name)")
+
+;; Profile carries :type, :name, :preferredUsername, :created
+(epoch 15)
+(eval "(get (erlang-eval-ast \"Obj = [{type, person}, {name, alice_name}, {preferredUsername, alice_local}], Act = [{actor, alice}, {type, create}, {object, Obj}, {published, 7}], S = actor_state:fold(Act, actor_state:new()), {ok, P} = actor_state:lookup(alice, S), {actor_state:profile_type(P), actor_state:profile_name(P), actor_state:profile_field(preferredUsername, P), actor_state:profile_field(created, P)} =:= {person, alice_name, {ok, alice_local}, {ok, 7}}\") :name)")
+
+;; Create{Service} also registers
+(epoch 16)
+(eval "(get (erlang-eval-ast \"Obj = [{type, service}, {name, feedbot}], Act = [{actor, feed1}, {type, create}, {object, Obj}, {published, 1}], S = actor_state:fold(Act, actor_state:new()), {ok, P} = actor_state:lookup(feed1, S), actor_state:profile_type(P) =:= service\") :name)")
+
+;; Create{Group} also registers
+(epoch 17)
+(eval "(get (erlang-eval-ast \"Obj = [{type, group}, {name, working_group}], Act = [{actor, wg1}, {type, create}, {object, Obj}, {published, 1}], S = actor_state:fold(Act, actor_state:new()), {ok, P} = actor_state:lookup(wg1, S), actor_state:profile_type(P) =:= group\") :name)")
+
+;; Create{Note} is pass-through (non-actor object)
+(epoch 18)
+(eval "(get (erlang-eval-ast \"Obj = [{type, note}, {content, hi}], Act = [{actor, alice}, {type, create}, {object, Obj}, {published, 1}], actor_state:fold(Act, actor_state:new()) =:= []\") :name)")
+
+;; Duplicate Create doesn't overwrite an existing profile
+(epoch 19)
+(eval "(get (erlang-eval-ast \"O1 = [{type, person}, {name, alice_v1}], O2 = [{type, person}, {name, alice_v2}], A1 = [{actor, alice}, {type, create}, {object, O1}, {published, 1}], A2 = [{actor, alice}, {type, create}, {object, O2}, {published, 2}], S1 = actor_state:fold(A1, actor_state:new()), S2 = actor_state:fold(A2, S1), {ok, P} = actor_state:lookup(alice, S2), actor_state:profile_name(P) =:= alice_v1\") :name)")
+
+;; Two distinct actors live side by side
+(epoch 20)
+(eval "(get (erlang-eval-ast \"PO = [{type, person}, {name, alice_n}], SO = [{type, service}, {name, bobbot_n}], A1 = [{actor, alice}, {type, create}, {object, PO}, {published, 1}], A2 = [{actor, bobbot}, {type, create}, {object, SO}, {published, 2}], S = actor_state:fold(A2, actor_state:fold(A1, actor_state:new())), actor_state:actors(S) =:= [alice, bobbot]\") :name)")
+
+;; Update merges patch
+(epoch 21)
+(eval "(get (erlang-eval-ast \"PO = [{type, person}, {name, alice_n}], A1 = [{actor, alice}, {type, create}, {object, PO}, {published, 1}], A2 = [{actor, alice}, {type, update}, {patch, [{summary, new_bio}]}, {published, 2}], S = actor_state:fold(A2, actor_state:fold(A1, actor_state:new())), {ok, P} = actor_state:lookup(alice, S), actor_state:profile_field(summary, P) =:= {ok, new_bio}\") :name)")
+
+;; Update overwrites individual fields (last-write-wins per key)
+(epoch 22)
+(eval "(get (erlang-eval-ast \"PO = [{type, person}, {name, alice_v1}], A1 = [{actor, alice}, {type, create}, {object, PO}, {published, 1}], A2 = [{actor, alice}, {type, update}, {patch, [{name, alice_v2}]}, {published, 2}], S = actor_state:fold(A2, actor_state:fold(A1, actor_state:new())), {ok, P} = actor_state:lookup(alice, S), actor_state:profile_name(P) =:= alice_v2\") :name)")
+
+;; Update for unknown actor is pass-through
+(epoch 23)
+(eval "(get (erlang-eval-ast \"A = [{actor, ghost}, {type, update}, {patch, [{summary, x}]}, {published, 1}], actor_state:fold(A, actor_state:new()) =:= []\") :name)")
+
+;; Move records :moved_to
+(epoch 24)
+(eval "(get (erlang-eval-ast \"PO = [{type, person}, {name, alice_n}], A1 = [{actor, alice}, {type, create}, {object, PO}, {published, 1}], A2 = [{actor, alice}, {type, move}, {moved_to, new_alice}, {published, 2}], S = actor_state:fold(A2, actor_state:fold(A1, actor_state:new())), {ok, P} = actor_state:lookup(alice, S), actor_state:profile_field(moved_to, P) =:= {ok, new_alice}\") :name)")
+
+;; fold_fn/0 is a 2-arity Erlang fun usable by projection:start_link
+(epoch 25)
+(eval "(get (erlang-eval-ast \"F = actor_state:fold_fn(), is_function(F, 2)\") :name)")
+
+;; fold ignores activities with no :actor field
+(epoch 26)
+(eval "(get (erlang-eval-ast \"Obj = [{type, person}, {name, x}], Act = [{type, create}, {object, Obj}, {published, 1}], actor_state:fold(Act, actor_state:new()) =:= []\") :name)")
+
+;; public_keys field is captured at Create time
+(epoch 27)
+(eval "(get (erlang-eval-ast \"Keys = [[{id, k1}, {value, <<1,2,3,4>>}]], Obj = [{type, person}, {name, alice_n}, {public_keys, Keys}], Act = [{actor, alice}, {type, create}, {object, Obj}, {published, 1}], S = actor_state:fold(Act, actor_state:new()), {ok, P} = actor_state:lookup(alice, S), actor_state:profile_field(public_keys, P) =:= {ok, Keys}\") :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: $actual
+"
+  fi
+}
+
+check  3  "actor_state module loaded"          "actor_state"
+check 10  "new/0 -> []"                        "true"
+check 11  "has/2 false on empty"               "true"
+check 12  "lookup/2 not_found on empty"        "true"
+check 13  "actors/1 [] on empty"               "true"
+check 14  "Create{Person} registers actor"    "true"
+check 15  "Profile carries type/name/created"  "true"
+check 16  "Create{Service} registers actor"    "true"
+check 17  "Create{Group} registers actor"      "true"
+check 18  "Create{Note} pass-through"          "true"
+check 19  "Duplicate Create no-overwrite"      "true"
+check 20  "Two actors side by side"            "true"
+check 21  "Update merges new fields"           "true"
+check 22  "Update last-write-wins per key"     "true"
+check 23  "Update unknown actor pass-through"  "true"
+check 24  "Move records :moved_to"             "true"
+check 25  "fold_fn/0 is fun/2"                 "true"
+check 26  "Activity sans :actor pass-through"  "true"
+check 27  "public_keys captured at Create"     "true"
+
+TOTAL=$((PASS+FAIL))
+if [ $FAIL -eq 0 ]; then
+  echo "ok $PASS/$TOTAL next/tests/actor_state_pure.sh passed"
+else
+  echo "FAIL $PASS/$TOTAL passed, $FAIL failed:"
+  echo "$ERRORS"
+fi
+[ $FAIL -eq 0 ]

plans/fed-sx-milestone-2.md

@@ -169,16 +169,25 @@ publicKey rotation history, profile fields, follower counts, etc.
   `bootstrap_load.sh` 15/15, `bootstrap_populate.sh` 14/14,
   `bootstrap_start.sh` 10/10). `bootstrap_build.sh` 12/12 picks
   up the new bundle CID dynamically.
-- [ ] **2b** — Actor-state projection fold (Erlang-fun stand-in,
-  mirrors Step 5d-pure's `define_registry`):
-  - On `Create{Person|Service|Group}`: register the actor's profile
-    in `{ActorId => #{type, name, preferredUsername, summary, icon,
-    public_keys, created}}`.
-  - On `Update{Person|Service|Group, patch}`: deep-merge the patch.
-  - On `Move`: record `:movedTo` pointer.
-  - `next/kernel/actor_state.erl` with `fold_fn/0` plugging into
-    `projection:start_link/3`. Pure-functional + gen_server-bridged
-    tests as a single `actor_state_pure.sh`.
+- [x] **2b** — Actor-state projection fold (Erlang-fun stand-in,
+  mirrors Step 5d-pure's `define_registry`). `next/kernel/actor_state.erl`
+  with state shape `[{ActorId, Profile}, ...]` where `Profile` is a
+  proplist with `:type / :name / :preferredUsername / :summary /
+  :icon / :public_keys / :moved_to / :created`. Maps `#{}` aren't
+  registered in the substrate, so the profile is a property list
+  (same shape choice as the kernel's bucket / registry state).
+  Folding rules:
+  - `Create{Person|Service|Group}` (from a known `:actor`):
+    captures profile fields + `:created` (=`:published` seq).
+    Duplicate Creates are no-overwrite.
+  - `Update{Person|Service|Group, patch}`: merges `:patch` into the
+    profile last-write-wins per key.
+  - `Move`: records `:moved_to` on the profile.
+  Other activity types and non-actor object Creates pass through.
+  `fold_fn/0` plugs into `projection:start_link/3`. Local
+  `find_keyed/has_keyed/set_keyed` helpers (same gap as 1a — no
+  `lists:keyfind`/`keymember` in the substrate). 19 cases in
+  `actor_state_pure.sh`.
 - [ ] **2c** — `nx_kernel:bootstrap_actor/4(ActorId, Profile,
   KeySpec, State)` — publishes `Create{Person{...}}` as the actor's
   first activity, exercising the full pipeline. Integration test
@@ -691,6 +700,18 @@ proceed.
 
 Newest first.
 
+- **2026-06-06** — Step 2b: actor-state projection Erlang module.
+  New `next/kernel/actor_state.erl` with `fold/2` over Create / Update
+  / Move activities. Profile is a property list of `:type / :name /
+  :preferredUsername / :summary / :icon / :public_keys / :moved_to /
+  :created`. Create captures fields and `:published` as `:created`;
+  duplicate Create is no-overwrite; non-actor Creates and `:actor`-
+  less envelopes pass through. Update last-write-wins per patch key.
+  Move records `:moved_to`. `fold_fn/0` is a 2-arity Erlang fun for
+  `projection:start_link/3` (structural twin of `define_registry`).
+  `next/tests/actor_state_pure.sh` 19/19. Conformance 761/761.
+  Step-2-adjacent no-regression gate 106/106 across 6 suites.
+
 - **2026-06-06** — Step 2a: genesis Person/Service/Group object-
   types. Three new SX files in `next/genesis/object-types/` with
   the same shape as `note.sx` / `sx-artifact.sx` (`:name`, `:doc`,