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/boot.sx

@@ -91,6 +91,32 @@
           (sx-hydrate-elements el))))))
 
 
+;; --------------------------------------------------------------------------
+;; Resolve Suspense — replace streaming placeholder with resolved content
+;; --------------------------------------------------------------------------
+;;
+;; 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.
+
+(define resolve-suspense
+  (fn (id sx)
+    (let ((el (dom-query (str "[data-suspense=\"" id "\"]"))))
+      (if el
+        (do
+          (let ((ast (parse sx))
+                (env (get-render-env nil))
+                (node (render-to-dom ast env nil)))
+            (dom-set-text-content el "")
+            (dom-append el node)
+            (process-elements el)
+            (sx-hydrate-elements el)
+            (dom-dispatch el "sx:resolved" {:id id})))
+        (log-warn (str "resolveSuspense: no element for id=" id))))))
+
+
 ;; --------------------------------------------------------------------------
 ;; Hydrate — render all [data-sx] elements
 ;; --------------------------------------------------------------------------