Phase 6: Streaming & Suspense — chunked HTML with suspense resolution

Server streams HTML shell with ~suspense placeholders immediately,
then sends resolution <script> chunks as async IO completes. Browser
renders loading skeletons instantly, replacing them with real content
as data arrives via __sxResolve().

- defpage :stream true opts pages into streaming response
- ~suspense component renders fallback with data-suspense attr
- resolve-suspense in boot.sx (spec) + bootstrapped to sx-browser.js
- __sxPending queue handles resolution before sx-browser.js loads
- execute_page_streaming() async generator with concurrent IO tasks
- Streaming demo page at /isomorphism/streaming with 1.5s simulated delay

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

shared/sx/ref/bootstrap_js.py

@@ -480,6 +480,7 @@ class JSEmitter:
             "init-style-dict": "initStyleDict",
             "SX_VERSION": "SX_VERSION",
             "boot-init": "bootInit",
+            "resolve-suspense": "resolveSuspense",
             "resolve-mount-target": "resolveMountTarget",
             "sx-render-with-env": "sxRenderWithEnv",
             "get-render-env": "getRenderEnv",
@@ -4020,6 +4021,7 @@ def public_api_js(has_html, has_sx, has_dom, has_engine, has_orch, has_cssx, has
         api_lines.append('    update: typeof sxUpdateElement === "function" ? sxUpdateElement : null,')
         api_lines.append('    renderComponent: typeof sxRenderComponent === "function" ? sxRenderComponent : null,')
         api_lines.append('    getEnv: function() { return componentEnv; },')
+        api_lines.append('    resolveSuspense: typeof resolveSuspense === "function" ? resolveSuspense : null,')
         api_lines.append('    init: typeof bootInit === "function" ? bootInit : null,')
     elif has_orch:
         api_lines.append('    init: typeof engineInit === "function" ? engineInit : null,')
@@ -4060,7 +4062,18 @@ def public_api_js(has_html, has_sx, has_dom, has_engine, has_orch, has_cssx, has
         api_lines.append('''
   // --- Auto-init ---
   if (typeof document !== "undefined") {
-    var _sxInit = function() { bootInit(); };
+    var _sxInit = function() {
+      bootInit();
+      // Process any suspense resolutions that arrived before init
+      if (global.__sxPending) {
+        for (var pi = 0; pi < global.__sxPending.length; pi++) {
+          resolveSuspense(global.__sxPending[pi].id, global.__sxPending[pi].sx);
+        }
+        global.__sxPending = null;
+      }
+      // Set up direct resolution for future chunks
+      global.__sxResolve = function(id, sx) { resolveSuspense(id, sx); };
+    };
     if (document.readyState === "loading") {
       document.addEventListener("DOMContentLoaded", _sxInit);
     } else {