review quick-wins: JIT gate, crash guards, crit-2 signal-return, regen repair

Server (sx_server.ml):
- HTTP mode: JIT hook now opt-in via SX_SERVING_JIT, matching epoch mode
  (was unconditional — live serving-JIT miscompiles J1/J2/J3 de-risked)
- command channel: malformed/non-ASCII line returns an error response
  instead of killing the shared process (C1/C1b)
- response cache: soft error pages no longer cached (S4);
  http_render_page returns (html, is_error)

Kernel spec + regen:
- crit-2: signal-return frame stored the saved kont under :f but the reader
  looked up "saved-kont" — handler value became the whole program's result
  and the covering test passed vacuously. Fixed; raise-continuable now also
  resumes at the raise site (rest-k, not unwound-k), mirroring signal-condition
- quasiquote: R7RS longhand unquote-splicing aliased to splice-unquote
  (used to serialize literally — silent zero-splice)
- guard: re-raise sentinel gensym'd per execution (was forgeable by any
  (list '__guard-reraise__ x) value)
- do: IIFE-head form no longer misparses as a Scheme do-loop
- render: area/base/embed/param/track added to HTML_TAGS (were void-only
  and rendered as Undefined symbol)
- REGEN REPAIR: checked-in sx_ref.ml carried hand-written additions that
  every regeneration silently lost (let-values/define-values/delay/
  delay-force registrations, AdtValue define-type) plus 5 regen blockers
  (arrow-name mangling, 3-arg get, &rest defines, HO-position helper refs,
  transpiler prim-table gaps). Moved into bootstrap.py FIXUPS/skips and the
  transpiler prim table — regen is now reproducible, compiles, and tests
  at baseline (CI Dockerfile.test steps 3-4 could not previously have
  produced a compiling kernel)

Primitives:
- contains?: dict key-check arm per its spec doc
- expt: promotes to float on int63 overflow ((expt 2 100) returned 0)
- mcp_tree parity with sx_primitives: get (Integer indices + 3-arg default),
  split (literal substring, was char-class — the historical gotcha lived
  here), empty? on ""/{}, contains?, equal?, keyword-name, char-code
  (Integer), parse-number (Integer-aware)

Python/docs:
- shared/sx/boundary.py: dead validation now logs a one-time WARNING instead
  of silently no-oping (full revival gated: tier-1 declarations deleted and
  SX_BOUNDARY_STRICT=1 is live in production compose)
- CLAUDE.md: canonical reference now points at spec/*.sx; island authoring
  rules corrected (let IS sequential, bodies ARE implicit begin)

Verification: full suite 5762 passed / 274 failed — fail set byte-identical
to the pre-change baseline (273 in-progress hs-* + pre-existing r7rs radix
shadow). All repros verified fixed on both the native binary and the rebuilt
WASM browser kernel. Review findings: /tmp/sx-review/*.md

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

hosts/ocaml/bin/mcp_tree.ml

@@ -375,18 +375,34 @@ let setup_env () =
     | [String s] when String.length s = 1 ->
       let c = s.[0] in Bool ((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z'))
     | _ -> Bool false);
+  (* Parity with sx_primitives: Integer, not float — make-char requires an
+     Integer codepoint, so the float version broke #\a char literals here. *)
   bind "char-code" (fun args -> match args with
-    | [String s] when String.length s > 0 -> Number (float_of_int (Char.code s.[0]))
-    | _ -> Number 0.0);
+    | [String s] when String.length s > 0 -> Integer (Char.code s.[0])
+    | _ -> Integer 0);
   bind "code-char" (fun args -> match args with
     | [Number n] -> String (String.make 1 (Char.chr (int_of_float n)))
     | _ -> String "");
+  (* Parity with sx_primitives: Integer-aware — the float-only version
+     shadowed the kernel one and broke rationals through the guest parser. *)
   bind "parse-number" (fun args -> match args with
-    | [String s] -> (try Number (float_of_string s) with _ -> Nil)
+    | [String s] ->
+      let has_dec = String.contains s '.' in
+      let has_exp = String.contains s 'e' || String.contains s 'E' in
+      if has_dec || has_exp then
+        (try Number (float_of_string s) with Failure _ -> Nil)
+      else
+        (match int_of_string_opt s with
+         | Some n -> Integer n
+         | None -> (try Number (float_of_string s) with Failure _ -> Nil))
     | _ -> Nil);
   bind "identical?" (fun args -> match args with
     | [a; b] -> Bool (a == b)
     | _ -> Bool false);
+  (* Parity with sx_server: equal? exists in the real runtime env *)
+  bind "equal?" (fun args -> match args with
+    | [a; b] -> Bool (a = b)
+    | _ -> raise (Eval_error "equal?: expected 2 args"));
   (* Character classification for SX parser.sx *)
   bind "ident-start?" (fun args -> match args with
     | [String s] when String.length s = 1 ->
@@ -427,8 +443,10 @@ let setup_env () =
   (* Runtime functions needed by tree-tools *)
   bind "symbol-name" (fun args -> match args with
     | [Symbol s] -> String s | _ -> String "");
+  (* Parity with sx_server: error on non-keyword (was a silent "") *)
   bind "keyword-name" (fun args -> match args with
-    | [Keyword k] -> String k | _ -> String "");
+    | [Keyword k] -> String k
+    | _ -> raise (Eval_error "keyword-name: expected keyword"));
   bind "make-symbol" (fun args -> match args with
     | [String s] -> Symbol s | _ -> Nil);
   (* Environment operations needed by harness *)
@@ -443,12 +461,30 @@ let setup_env () =
     | _ -> Bool false);
   bind "make-env" (fun _args -> Env (make_env ()));
   bind "keys" (fun args -> match args with
-    | [Dict d] -> List (Hashtbl.fold (fun k _ acc -> String k :: acc) d [])
+    | [Dict d] -> List (dict_keys d)
     | _ -> List []);
-  bind "get" (fun args -> match args with
-    | [Dict d; String k] -> (match Hashtbl.find_opt d k with Some v -> v | None -> Nil)
-    | [Dict d; Keyword k] -> (match Hashtbl.find_opt d k with Some v -> v | None -> Nil)
-    | [List items; Number n] -> (let i = int_of_float n in if i >= 0 && i < List.length items then List.nth items i else Nil)
+  (* Parity with sx_primitives: Integer indices (literals parse as Integer,
+     so the Number-only arm returned nil for every (get lst 1)), Symbol keys,
+     and the 3-arg default form — default only when the key is ABSENT. *)
+  bind "get" (fun args ->
+    let dict_key = function
+      | String k | Keyword k | Symbol k -> Some k
+      | _ -> None in
+    let list_idx = function
+      | Integer i -> Some i
+      | Number n -> Some (int_of_float n)
+      | _ -> None in
+    match args with
+    | [Dict d; key] | [Dict d; key; _] when dict_key key <> None && Hashtbl.mem d (Option.get (dict_key key)) ->
+      Hashtbl.find d (Option.get (dict_key key))
+    | [Dict _; _] -> Nil
+    | [Dict _; _; default] -> default
+    | ([List items; idx] | [ListRef { contents = items }; idx]) when list_idx idx <> None ->
+      (let i = Option.get (list_idx idx) in
+       if i >= 0 && i < List.length items then List.nth items i else Nil)
+    | ([List items; idx; default] | [ListRef { contents = items }; idx; default]) when list_idx idx <> None ->
+      (let i = Option.get (list_idx idx) in
+       if i >= 0 && i < List.length items then List.nth items i else default)
     | _ -> Nil);
   bind "dict-set!" (fun args -> match args with
     | [Dict d; String k; v] -> Hashtbl.replace d k v; v
@@ -478,8 +514,12 @@ let setup_env () =
     | [Number _] -> Bool true | _ -> Bool false);
   bind "callable?" (fun args -> match args with
     | [NativeFn _ | Lambda _ | Component _ | Island _ | VmClosure _] -> Bool true | _ -> Bool false);
+  (* Parity with sx_primitives: empty string and empty dict are empty
+     (test-primitives.sx:89 asserts this; the old arms said false). *)
   bind "empty?" (fun args -> match args with
     | [List []] | [ListRef { contents = [] }] -> Bool true
+    | [String s] -> Bool (String.length s = 0)
+    | [Dict d] -> Bool (Hashtbl.length d = 0)
     | [Nil] -> Bool true | _ -> Bool false);
   bind "contains?" (fun args -> match args with
     | [String s; String sub] ->
@@ -490,6 +530,11 @@ let setup_env () =
       in Bool (String.length sub = 0 || find 0)
     | [List l; v] | [ListRef { contents = l }; v] ->
       Bool (List.exists (fun x -> x = v) l)
+    | [Dict d; key] ->
+      (* Dicts: key check — matches the sx_primitives fix *)
+      (match key with
+       | String k | Keyword k | Symbol k -> Bool (Hashtbl.mem d k)
+       | _ -> Bool false)
     | _ -> Bool false);
   bind "starts-with?" (fun args -> match args with
     | [String s; String prefix] ->
@@ -560,9 +605,28 @@ let setup_env () =
     | _ -> Nil);
   bind "trim" (fun args -> match args with
     | [String s] -> String (String.trim s) | _ -> String "");
+  (* Parity with sx_primitives: literal SUBSTRING separator (the old
+     split_on_char d.[0] was char-class semantics — the historical
+     "split is char-class" gotcha lived HERE, not in the kernel), keeps
+     empties, empty separator → chars, and no crash on "". *)
   bind "split" (fun args -> match args with
-    | [String s; String d] ->
-      List (List.map (fun p -> String p) (String.split_on_char d.[0] s))
+    | [String s; String sep] ->
+      let sl = String.length s and pl = String.length sep in
+      if pl = 0 then
+        List (List.init sl (fun i -> String (String.make 1 s.[i])))
+      else if pl = 1 then
+        List (List.map (fun p -> String p) (String.split_on_char sep.[0] s))
+      else begin
+        let parts = ref [] and start = ref 0 and i = ref 0 in
+        while !i <= sl - pl do
+          if String.sub s !i pl = sep then begin
+            parts := String.sub s !start (!i - !start) :: !parts;
+            start := !i + pl; i := !i + pl
+          end else incr i
+        done;
+        parts := String.sub s !start (sl - !start) :: !parts;
+        List (List.map (fun p -> String p) (List.rev !parts))
+      end
     | _ -> List []);
   (* sx-parse — use the native OCaml parser for bootstrapping *)
   bind "sx-parse" (fun args -> match args with