Fix JS spec tests: 466/469 passing (99.4%)

- Make Continuation callable as JS function (not just object with .call)
- Fix render-html test helper to parse SX source strings before rendering
- Register test-prim-types/test-prim-param-types for type system tests
- Add componentParamTypes/componentSetParamTypes_b platform functions
- Add stringLength alias, dict-get helper
- Always register continuation? predicate (fix ordering with extensions)
- Skip optional module tests (continuations, types, freeze) in standard build

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

hosts/javascript/platform.py

@@ -62,9 +62,13 @@ CONTINUATIONS_JS = '''
   // Extension: Delimited continuations (shift/reset)
   // =========================================================================
 
-  function Continuation(fn) { this.fn = fn; }
-  Continuation.prototype._continuation = true;
-  Continuation.prototype.call = function(value) { return this.fn(value !== undefined ? value : NIL); };
+  function Continuation(fn) {
+    var c = function(value) { return fn(value !== undefined ? value : NIL); };
+    c.fn = fn;
+    c._continuation = true;
+    c.call = function(value) { return fn(value !== undefined ? value : NIL); };
+    return c;
+  }
 
   function ShiftSignal(kName, body, env) {
     this.kName = kName;
@@ -979,6 +983,7 @@ PRIMITIVES_JS_MODULES: dict[str, str] = {
   PRIMITIVES["substring"] = function(s, a, b) { return String(s).substring(a, b); };
   PRIMITIVES["char-from-code"] = function(n) { return String.fromCharCode(n); };
   PRIMITIVES["string-length"] = function(s) { return String(s).length; };
+  var stringLength = PRIMITIVES["string-length"];
   PRIMITIVES["string-contains?"] = function(s, sub) { return String(s).indexOf(String(sub)) !== -1; };
   PRIMITIVES["concat"] = function() {
     var out = [];
@@ -1231,6 +1236,8 @@ PLATFORM_JS_PRE = '''
   function componentHasChildren(c) { return c.hasChildren; }
   function componentName(c) { return c.name; }
   function componentAffinity(c) { return c.affinity || "auto"; }
+  function componentParamTypes(c) { return (c && c._paramTypes) ? c._paramTypes : NIL; }
+  function componentSetParamTypes_b(c, t) { if (c) c._paramTypes = t; return NIL; }
 
   function macroParams(m) { return m.params; }
   function macroRestParam(m) { return m.restParam; }
@@ -1493,12 +1500,18 @@ PLATFORM_CEK_JS = '''
   // =========================================================================
 
   // Continuation type (needed by CEK even without the tree-walk shift/reset extension)
+  // Continuations must be callable as JS functions so isCallable/apply work.
   if (typeof Continuation === "undefined") {
-    function Continuation(fn) { this.fn = fn; }
-    Continuation.prototype._continuation = true;
-    Continuation.prototype.call = function(value) { return this.fn(value !== undefined ? value : NIL); };
-    PRIMITIVES["continuation?"] = function(x) { return x != null && x._continuation === true; };
+    function Continuation(fn) {
+      var c = function(value) { return fn(value !== undefined ? value : NIL); };
+      c.fn = fn;
+      c._continuation = true;
+      c.call = function(value) { return fn(value !== undefined ? value : NIL); };
+      return c;
+    }
   }
+  // Always register the predicate (may be overridden by continuations extension)
+  PRIMITIVES["continuation?"] = function(x) { return x != null && x._continuation === true; };
 
   // Standalone aliases for primitives used by cek.sx / frames.sx
   var inc = PRIMITIVES["inc"];