WIP: bytecode module pre-compilation and loading infrastructure

- compile-modules.js: Node.js build tool, all 23 .sx files compile to .sxbc.json
- api_load_module with shared globals (beginModuleLoad/endModuleLoad batch API)
- api_compile_module for runtime compilation
- sx-platform.js: bytecode-first loader with source fallback, JSON deserializer
- Deferred JIT enable (setTimeout after boot)

Known issues:
- WASM browser: loadModule loads but functions not accessible (env writeback
  issue with interned keys)
- WASM browser: compileModule fails ("Not callable: nil" — compile-module
  function from bytecode not working correctly in WASM context)
- Node.js js_of_ocaml: full roundtrip works (compile → load → call)

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

hosts/ocaml/browser/sx_browser.ml

@@ -231,17 +231,46 @@ let api_load src_js =
   | Eval_error msg -> Js.Unsafe.inject (Js.string ("Error: " ^ msg))
   | Parse_error msg -> Js.Unsafe.inject (Js.string ("Parse error: " ^ msg))
 
+(* Shared globals table for batch module loading.
+   Created by beginModuleLoad, accumulated across loadModule calls,
+   flushed to env by endModuleLoad. Ensures closures from early
+   modules can see definitions from later modules. *)
+let _module_globals : (string, value) Hashtbl.t option ref = ref None
+
+let api_begin_module_load () =
+  let g = Hashtbl.create 512 in
+  Hashtbl.iter (fun id v -> Hashtbl.replace g (unintern id) v) global_env.bindings;
+  _module_globals := Some g;
+  Js.Unsafe.inject true
+
+let api_end_module_load () =
+  (match !_module_globals with
+   | Some g ->
+     Hashtbl.iter (fun k v ->
+       Hashtbl.replace global_env.bindings (intern k) v
+     ) g;
+     _module_globals := None
+   | None -> ());
+  Js.Unsafe.inject true
+
 let api_load_module module_js =
   try
     let code_val = js_to_value module_js in
     let code = Sx_vm.code_from_value code_val in
-    let globals = Hashtbl.create 256 in
-    Hashtbl.iter (fun id v -> Hashtbl.replace globals (unintern id) v) global_env.bindings;
+    let globals = match !_module_globals with
+      | Some g -> g  (* use shared table *)
+      | None ->
+        (* standalone mode: create temp table *)
+        let g = Hashtbl.create 256 in
+        Hashtbl.iter (fun id v -> Hashtbl.replace g (unintern id) v) global_env.bindings;
+        g
+    in
     let _result = Sx_vm.execute_module code globals in
-    (* Copy all globals back into env — new defines + unchanged values *)
-    Hashtbl.iter (fun k v ->
-      Hashtbl.replace global_env.bindings (intern k) v
-    ) globals;
+    (* If standalone (no batch), copy back immediately *)
+    if !_module_globals = None then
+      Hashtbl.iter (fun k v ->
+        Hashtbl.replace global_env.bindings (intern k) v
+      ) globals;
     Js.Unsafe.inject (Hashtbl.length globals)
   with
   | Eval_error msg -> Js.Unsafe.inject (Js.string ("Error: " ^ msg))
@@ -653,6 +682,8 @@ let () =
   Js.Unsafe.set sx (Js.string "renderToHtml") (Js.wrap_callback api_render_to_html);
   Js.Unsafe.set sx (Js.string "load") (Js.wrap_callback api_load);
   Js.Unsafe.set sx (Js.string "loadModule") (Js.wrap_callback api_load_module);
+  Js.Unsafe.set sx (Js.string "beginModuleLoad") (Js.wrap_callback (fun () -> api_begin_module_load ()));
+  Js.Unsafe.set sx (Js.string "endModuleLoad") (Js.wrap_callback (fun () -> api_end_module_load ()));
   Js.Unsafe.set sx (Js.string "compileModule") (wrap api_compile_module);
   Js.Unsafe.set sx (Js.string "typeOf") (Js.wrap_callback api_type_of);
   Js.Unsafe.set sx (Js.string "inspect") (Js.wrap_callback api_inspect);