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>

shared/static/wasm/sx-platform.js

@@ -197,6 +197,70 @@
     }
   })();
 
+  /**
+   * Deserialize type-tagged JSON constant back to JS value for loadModule.
+   */
+  function deserializeConstant(c) {
+    if (!c || !c.t) return null;
+    switch (c.t) {
+      case 's': return c.v;
+      case 'n': return c.v;
+      case 'b': return c.v;
+      case 'nil': return null;
+      case 'sym': return { _type: 'symbol', name: c.v };
+      case 'kw':  return { _type: 'keyword', name: c.v };
+      case 'list': return { _type: 'list', items: (c.v || []).map(deserializeConstant) };
+      case 'code': return {
+        _type: 'dict',
+        bytecode: { _type: 'list', items: c.v.bytecode },
+        constants: { _type: 'list', items: (c.v.constants || []).map(deserializeConstant) },
+        arity: c.v.arity || 0,
+        'upvalue-count': c.v['upvalue-count'] || 0,
+        locals: c.v.locals || 0,
+      };
+      case 'dict': {
+        var d = { _type: 'dict' };
+        for (var k in c.v) d[k] = deserializeConstant(c.v[k]);
+        return d;
+      }
+      default: return null;
+    }
+  }
+
+  /**
+   * Try loading a pre-compiled .sxbc.json bytecode module.
+   * Returns true on success, null on failure (caller falls back to .sx source).
+   */
+  function loadBytecodeFile(path) {
+    var bcPath = path.replace(/\.sx$/, '.sxbc.json');
+    var url = _baseUrl + bcPath + _cacheBust;
+    try {
+      var xhr = new XMLHttpRequest();
+      xhr.open("GET", url, false);
+      xhr.send();
+      if (xhr.status !== 200) return null;
+
+      var json = JSON.parse(xhr.responseText);
+      if (!json.module || json.magic !== 'SXBC') return null;
+
+      var module = {
+        _type: 'dict',
+        bytecode: { _type: 'list', items: json.module.bytecode },
+        constants: { _type: 'list', items: json.module.constants.map(deserializeConstant) },
+      };
+
+      var result = K.loadModule(module);
+      if (typeof result === 'string' && result.indexOf('Error') === 0) {
+        console.warn("[sx-platform] bytecode FAIL " + path + ":", result);
+        return null;
+      }
+      console.log("[sx-platform]  ok " + path + " (bytecode)");
+      return true;
+    } catch(e) {
+      return null;
+    }
+  }
+
   /**
    * Load an .sx file synchronously via XHR (boot-time only).
    * Returns the number of expressions loaded, or an error string.
@@ -227,7 +291,7 @@
 
   /**
    * Load all web adapter .sx files in dependency order.
-   * Called after the 8 FFI primitives are registered.
+   * Tries pre-compiled bytecode first, falls back to source.
    */
   function loadWebStack() {
     var files = [
@@ -264,12 +328,19 @@
       "sx/boot.sx",
     ];
 
-    var loaded = 0;
+    var loaded = 0, bcCount = 0, srcCount = 0;
+    if (K.beginModuleLoad) K.beginModuleLoad();
     for (var i = 0; i < files.length; i++) {
-      var r = loadSxFile(files[i]);
-      if (typeof r === "number") loaded += r;
+      var r = loadBytecodeFile(files[i]);
+      if (r) { bcCount++; continue; }
+      // Bytecode not available — end batch, load source, restart batch
+      if (K.endModuleLoad) K.endModuleLoad();
+      r = loadSxFile(files[i]);
+      if (typeof r === "number") { loaded += r; srcCount++; }
+      if (K.beginModuleLoad) K.beginModuleLoad();
     }
-    console.log("[sx-platform] Loaded " + loaded + " expressions from " + files.length + " files");
+    if (K.endModuleLoad) K.endModuleLoad();
+    console.log("[sx-platform] Loaded " + files.length + " files (" + bcCount + " bytecode, " + srcCount + " source, " + loaded + " exprs)");
     return loaded;
   }
 
@@ -339,7 +410,8 @@
     var _doInit = function() {
       loadWebStack();
       Sx.init();
-      K.eval('(enable-jit!)');
+      // Enable JIT after all boot code has run
+      setTimeout(function() { K.eval('(enable-jit!)'); }, 0);
     };
 
     if (document.readyState === "loading") {