Fix JIT compiler, CSSX browser support, double-fetch, SPA layout

JIT compiler:
- Fix jit_compile_lambda: resolve `compile` via symbol lookup in env
  instead of embedding VmClosure in AST (CEK dispatches differently)
- Register eval-defcomp/eval-defisland/eval-defmacro runtime helpers
  in browser kernel for bytecoded defcomp forms
- Disable broken .sxbc.json path (missing arity in nested code blocks),
  use .sxbc text format only
- Mark JIT-failed closures as sentinel to stop retrying

CSSX in browser:
- Add cssx.sx symlink + cssx.sxbc to browser web stack
- Add flush-cssx! to orchestration.sx post-swap for SPA nav
- Add cssx.sx to compile-modules.js and mcp_tree.ml bytecode lists

SPA navigation:
- Fix double-fetch: check e.defaultPrevented in click delegation
  (bind-event already handled the click)
- Fix layout destruction: change nav links from outerHTML to innerHTML
  swap (outerHTML destroyed #main-panel when response lacked it)
- Guard JS popstate handler when SX engine is booted
- Rename sx-platform.js → sx-platform-2.js to bust immutable cache

Playwright tests:
- Add trackErrors() helper to all test specs
- Add SPA DOM comparison test (SPA nav vs fresh load)
- Add single-fetch + no-duplicate-elements test
- Improve MCP tool output: show failure details and error messages

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

shared/static/wasm/sx-platform-2.js

@@ -233,31 +233,9 @@
    * Returns true on success, null on failure (caller falls back to .sx source).
    */
   function loadBytecodeFile(path) {
-    // Try .sxbc.json (JSON dict format)
-    var jsonPath = path.replace(/\.sx$/, '.sxbc.json');
-    var jsonUrl = _baseUrl + jsonPath + _cacheBust;
-    try {
-      var xhr = new XMLHttpRequest();
-      xhr.open("GET", jsonUrl, false);
-      xhr.send();
-      if (xhr.status === 200) {
-        var json = JSON.parse(xhr.responseText);
-        if (json.module && json.magic === 'SXBC') {
-          var module = {
-            _type: 'dict',
-            arity: json.module.arity || 0,
-            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.log("[sx-platform]  ok " + path + " (bytecode-json)");
-            return true;
-          }
-          console.warn("[sx-platform] bytecode-json FAIL " + path + ":", result);
-        }
-      }
-    } catch(e) { /* fall through to .sxbc */ }
+    console.log("[sx-platform] loadBytecodeFile:", path, "(sxbc-only, no json)");
+    // .sxbc.json path removed — the JSON format had a bug (missing arity
+    // in nested code blocks). Use .sxbc (SX text) format only.
 
     // Try .sxbc (SX s-expression format, loaded via load-sxbc primitive)
     var sxbcPath = path.replace(/\.sx$/, '.sxbc');
@@ -336,6 +314,8 @@
       "sx/adapter-html.sx",
       "sx/adapter-sx.sx",
       "sx/adapter-dom.sx",
+      // Client libraries (CSSX etc. — needed by page components)
+      "sx/cssx.sx",
       // Boot helpers (platform functions in pure SX)
       "sx/boot-helpers.sx",
       "sx/hypersx.sx",
@@ -418,22 +398,18 @@
             "hydrated:", !!islands[j]._sxBoundislandhydrated || !!islands[j]["_sxBound" + "island-hydrated"],
             "children:", islands[j].children.length);
         }
-        // Register popstate handler for back/forward navigation.
-        // Fetch HTML (not SX) and extract #main-panel content.
+        // Fallback popstate handler for back/forward navigation.
+        // Only fires before SX engine boots — after boot, boot.sx registers
+        // its own popstate handler via handle-popstate in orchestration.sx.
         window.addEventListener("popstate", function() {
+          if (document.documentElement.hasAttribute("data-sx-ready")) return;
           var url = location.pathname + location.search;
           var target = document.querySelector("#main-panel");
           if (!target) return;
-          // Try client-side route first
-          var clientHandled = false;
-          try { clientHandled = K.eval('(try-client-route "' + url.replace(/"/g, '\\"') + '" "#main-panel")'); } catch(e) {}
-          if (clientHandled) return;
-          // Server fetch — request full HTML (no SX-Request header)
           fetch(url)
             .then(function(r) { return r.text(); })
             .then(function(html) {
               if (!html) return;
-              // Parse the full HTML and extract #main-panel
               var parser = new DOMParser();
               var doc = parser.parseFromString(html, "text/html");
               var srcPanel = doc.querySelector("#main-panel");
@@ -441,26 +417,20 @@
               if (srcPanel) {
                 target.outerHTML = srcPanel.outerHTML;
               }
-              // Also update nav if present
               var navTarget = document.querySelector("#sx-nav");
               if (srcNav && navTarget) {
                 navTarget.outerHTML = srcNav.outerHTML;
               }
-              // Re-hydrate
-              var newTarget = document.querySelector("#main-panel");
-              if (newTarget) {
-                try { K.eval("(post-swap (dom-query \"#main-panel\"))"); } catch(e) {}
-                try { K.eval("(sx-hydrate-islands (dom-query \"#main-panel\"))"); } catch(e) {}
-              }
             })
             .catch(function(e) { console.warn("[sx] popstate fetch error:", e); });
         });
-        // Event delegation for sx-get links — bytecoded bind-event doesn't
-        // attach per-element listeners (VM closure issue), so catch clicks
-        // at the document level and route through the SX engine.
+        // Event delegation for sx-get links — fallback when bind-event's
+        // per-element listener didn't attach. If bind-event DID fire, it
+        // already called preventDefault — skip to avoid double-fetch.
         document.addEventListener("click", function(e) {
           var el = e.target.closest("a[sx-get]");
           if (!el) return;
+          if (e.defaultPrevented) return;
           if (e.metaKey || e.ctrlKey || e.shiftKey || e.altKey) return;
           e.preventDefault();
           var url = el.getAttribute("href") || el.getAttribute("sx-get");

shared/static/wasm/sx/cssx.sx

@@ -0,0 +1 @@
+../../../../shared/sx/templates/cssx.sx

shared/static/wasm/sx/orchestration.sx

@@ -256,6 +256,25 @@
             "sx:afterSwap"
             (dict "target" target-el "swap" swap-style)))))))
 
+(define
+  flush-cssx!
+  :effects (mutation io)
+  (fn
+    ()
+    (let
+      ((rules (collected "cssx")))
+      (clear-collected! "cssx")
+      (when
+        (not (empty? rules))
+        (let
+          ((style (dom-query "#sx-css")))
+          (when
+            style
+            (dom-set-prop
+              style
+              "textContent"
+              (str (dom-get-prop style "textContent") (join "" rules)))))))))
+
 (define
   handle-sx-response
   :effects (mutation io)
@@ -508,7 +527,8 @@
     (sx-hydrate root)
     (sx-hydrate-islands root)
     (run-post-render-hooks)
-    (process-elements root)))
+    (process-elements root)
+    (flush-cssx!)))
 
 (define
   process-settle-hooks

shared/static/wasm/sx_browser.bc.wasm.js

@@ -1792,7 +1792,7 @@
             blake2_js_for_wasm_create: blake2_js_for_wasm_create};
    }
    (globalThis))
-({"link":[["runtime-0db9b496",0],["prelude-d7e4b000",0],["stdlib-23ce0836",[]],["sx-15eb71d8",[2]],["jsoo_runtime-f96b44a8",[2]],["js_of_ocaml-651f6707",[2,4]],["dune__exe__Sx_browser-0c758f5b",[2,3,5]],["std_exit-10fb8830",[2]],["start-80fdb768",0]],"generated":(b=>{var
+({"link":[["runtime-0db9b496",0],["prelude-d7e4b000",0],["stdlib-23ce0836",[]],["sx-eb076217",[2]],["jsoo_runtime-f96b44a8",[2]],["js_of_ocaml-651f6707",[2,4]],["dune__exe__Sx_browser-36a151d2",[2,3,5]],["std_exit-10fb8830",[2]],["start-80fdb768",0]],"generated":(b=>{var
 c=b,a=b?.module?.export||b;return{"env":{"caml_ba_kind_of_typed_array":()=>{throw new
 Error("caml_ba_kind_of_typed_array not implemented")},"caml_exn_with_js_backtrace":()=>{throw new
 Error("caml_exn_with_js_backtrace not implemented")},"caml_int64_create_lo_mi_hi":()=>{throw new