Decouple core evaluator from web platform, extract libraries

The core evaluator (spec/evaluator.sx) is now the irreducible computational
core with zero web, rendering, or type-system knowledge. 2531 → 2313 lines.

- Add extensible special form registry (*custom-special-forms* + register-special-form!)
- Add render dispatch hooks (*render-check* / *render-fn*) replacing hardcoded render-active?/is-render-expr?/render-expr
- Extract freeze scopes → spec/freeze.sx (library, not core)
- Extract content addressing → spec/content.sx (library, not core)
- Move sf-deftype/sf-defeffect → spec/types.sx (self-registering)
- Move sf-defstyle → web/forms.sx (self-registering with all web forms)
- Move web tests (defpage, streaming) → web/tests/test-forms.sx
- Add is-else-clause? helper (replaces 5 inline patterns)
- Make escape-html/escape-attr library functions in render.sx (pure SX, not platform-provided)
- Add foundations plan: Step 3.5 (data representations), Step 3.7 (verified components), OCaml for Step 4d
- Update all three bootstrappers (JS 957/957, Python 744/744, OCaml 952/952)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

hosts/ocaml/bootstrap.py

@@ -43,16 +43,30 @@ PREAMBLE = """\
 open Sx_types
 open Sx_runtime
 
-(* Trampoline — evaluates thunks via the CEK machine.
-   eval_expr is defined in the transpiled block below. *)
-let trampoline v = v  (* CEK machine doesn't produce thunks *)
+(* Trampoline — forward ref, resolved after eval_expr is defined. *)
+let trampoline_fn : (value -> value) ref = ref (fun v -> v)
+let trampoline v = !trampoline_fn v
+
+
+
+(* === Mutable state for strict mode === *)
+(* These are defined as top-level refs because the transpiler cannot handle
+   global set! mutation (it creates local refs that shadow the global). *)
+let _strict_ref = ref (Bool false)
+let _prim_param_types_ref = ref Nil
 
 """
 
 
-# OCaml fixups — override iterative CEK run
+# OCaml fixups — wire up trampoline + iterative CEK run
 FIXUPS = """\
 
+(* Wire up trampoline to resolve thunks via the CEK machine *)
+let () = trampoline_fn := (fun v ->
+  match v with
+  | Thunk (expr, env) -> eval_expr expr (Env env)
+  | _ -> v)
+
 (* Override recursive cek_run with iterative loop *)
 let cek_run_iterative state =
   let s = ref state in
@@ -122,7 +136,63 @@ def compile_spec_to_ml(spec_dir: str | None = None) -> str:
         parts.append(result)
 
     parts.append(FIXUPS)
-    return "\n".join(parts)
+    output = "\n".join(parts)
+
+    # Post-process: fix mutable globals that the transpiler can't handle.
+    # The transpiler emits local refs for set! targets within functions,
+    # but top-level globals (*strict*, *prim-param-types*) need to use
+    # the pre-declared refs from the preamble.
+    import re
+
+    # Fix *strict*: use _strict_ref instead of immutable let rec binding
+    output = re.sub(
+        r'and _strict_ =\n  \(Bool false\)',
+        'and _strict_ = !_strict_ref',
+        output,
+    )
+    # Fix set-strict!: use _strict_ref instead of local ref
+    output = re.sub(
+        r'and set_strict_b val\' =\n  let _strict_ = ref Nil in \(_strict_ := val\'; Nil\)',
+        "and set_strict_b val' =\n  _strict_ref := val'; Nil",
+        output,
+    )
+    # Fix *prim-param-types*: use _prim_param_types_ref
+    output = re.sub(
+        r'and _prim_param_types_ =\n  Nil',
+        'and _prim_param_types_ = !_prim_param_types_ref',
+        output,
+    )
+    # Fix set-prim-param-types!: use _prim_param_types_ref
+    output = re.sub(
+        r'and set_prim_param_types_b types =\n  let _prim_param_types_ = ref Nil in \(_prim_param_types_ := types; Nil\)',
+        "and set_prim_param_types_b types =\n  _prim_param_types_ref := types; Nil",
+        output,
+    )
+
+    # Fix all runtime reads of _strict_ and _prim_param_types_ to deref
+    # the mutable refs instead of using the stale let-rec bindings.
+    # This is needed because let-rec value bindings capture initial values.
+    # Use regex with word boundary to avoid replacing _strict_ref with
+    # !_strict_refref.
+    def fix_mutable_reads(text):
+        lines = text.split('\n')
+        fixed = []
+        for line in lines:
+            # Skip the definition lines
+            stripped = line.strip()
+            if stripped.startswith('and _strict_ =') or stripped.startswith('and _prim_param_types_ ='):
+                fixed.append(line)
+                continue
+            # Replace _strict_ as a standalone identifier only (not inside
+            # other names like set_strict_b). Match when preceded by space,
+            # paren, or start-of-line, and followed by space, paren, or ;.
+            line = re.sub(r'(?<=[ (])_strict_(?=[ );])', '!_strict_ref', line)
+            line = re.sub(r'(?<=[ (])_prim_param_types_(?=[ );])', '!_prim_param_types_ref', line)
+            fixed.append(line)
+        return '\n'.join(fixed)
+    output = fix_mutable_reads(output)
+
+    return output
 
 
 def main():