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/static/scripts/sx.js

@@ -1588,6 +1588,32 @@
     isTruthy: isSxTruthy,
     isNil: isNil,
 
+    /**
+     * Resolve a streaming suspense placeholder.
+     * Called by inline <script> tags that arrive during chunked transfer:
+     *   __sxResolve("content", "(~article :title \"Hello\")")
+     *
+     * Finds the suspense wrapper by data-suspense attribute, renders the
+     * new SX content, and replaces the wrapper's children.
+     */
+    resolveSuspense: function (id, sx) {
+      var el = document.querySelector('[data-suspense="' + id + '"]');
+      if (!el) {
+        console.warn("[sx] resolveSuspense: no element for id=" + id);
+        return;
+      }
+      try {
+        var node = Sx.render(sx);
+        el.textContent = "";
+        el.appendChild(node);
+        if (typeof SxEngine !== "undefined") SxEngine.process(el);
+        Sx.hydrate(el);
+        el.dispatchEvent(new CustomEvent("sx:resolved", { bubbles: true, detail: { id: id } }));
+      } catch (e) {
+        console.error("[sx] resolveSuspense error for id=" + id, e);
+      }
+    },
+
     /**
      * Mount a sx expression into a DOM element, replacing its contents.
      *   Sx.mount(el, '(~card :title "Hi")')
@@ -3164,6 +3190,15 @@
       Sx.processScripts();
       Sx.hydrate();
       SxEngine.process();
+      // Process any streaming suspense resolutions that arrived before init
+      if (global.__sxPending) {
+        for (var pi = 0; pi < global.__sxPending.length; pi++) {
+          Sx.resolveSuspense(global.__sxPending[pi].id, global.__sxPending[pi].sx);
+        }
+        global.__sxPending = null;
+      }
+      // Replace bootstrap resolver with direct calls
+      global.__sxResolve = function (id, sx) { Sx.resolveSuspense(id, sx); };
     };
     if (document.readyState === "loading") {
       document.addEventListener("DOMContentLoaded", init);