Phase 4: Client-side rendering of :data pages via abstract resolve-page-data

Spec layer (orchestration.sx):
- try-client-route now handles :data pages instead of falling back to server
- New abstract primitive resolve-page-data(name, params, callback) — platform
  decides transport (HTTP, IPC, cache, etc)
- Extracted swap-rendered-content and resolve-route-target helpers

Platform layer (bootstrap_js.py):
- resolvePageData() browser implementation: fetches /sx/data/<name>, parses
  SX response, calls callback. Other hosts provide their own transport.

Server layer (pages.py):
- evaluate_page_data() evaluates :data expr, serializes result as SX
- auto_mount_page_data() mounts /sx/data/ endpoint with per-page auth
- _build_pages_sx now computes component deps for all pages (not just pure)

Test page at /isomorphism/data-test exercises the full pipeline.

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

sx/sxc/pages/docs.sx

@@ -449,6 +449,20 @@
     :pages pages :total-pages total-pages :client-count client-count
     :server-count server-count :registry-sample registry-sample))
 
+(defpage data-test
+  :path "/isomorphism/data-test"
+  :auth :public
+  :layout (:sx-section
+    :section "Isomorphism"
+    :sub-label "Isomorphism"
+    :sub-href "/isomorphism/"
+    :sub-nav (~section-nav :items isomorphism-nav-items :current "Data Test")
+    :selected "Data Test")
+  :data (data-test-data)
+  :content (~data-test-content
+    :server-time server-time :items items
+    :phase phase :transport transport))
+
 ;; ---------------------------------------------------------------------------
 ;; Plans section
 ;; ---------------------------------------------------------------------------

sx/sxc/pages/helpers.py

@@ -23,6 +23,7 @@ def _register_sx_helpers() -> None:
         "bootstrapper-data": _bootstrapper_data,
         "bundle-analyzer-data": _bundle_analyzer_data,
         "routing-analyzer-data": _routing_analyzer_data,
+        "data-test-data": _data_test_data,
     })
 
 
@@ -488,3 +489,26 @@ def _event_detail_data(slug: str) -> dict:
         "event-example": detail.get("example"),
         "event-demo": sx_call(demo_name) if demo_name else None,
     }
+
+
+def _data_test_data() -> dict:
+    """Return test data for the client-side data rendering test page.
+
+    This exercises the Phase 4 data endpoint: server evaluates this
+    helper, serializes the result as SX, the client fetches and parses
+    it, then renders the page content with these bindings.
+    """
+    from datetime import datetime, timezone
+
+    return {
+        "server-time": datetime.now(timezone.utc).isoformat(timespec="seconds"),
+        "items": [
+            {"label": "Eval", "detail": "Server evaluates :data expression"},
+            {"label": "Serialize", "detail": "Result serialized as SX wire format"},
+            {"label": "Fetch", "detail": "Client calls resolve-page-data"},
+            {"label": "Parse", "detail": "Client parses SX response to dict"},
+            {"label": "Render", "detail": "Client merges data into env, renders content"},
+        ],
+        "phase": "Phase 4 — Client Async & IO Bridge",
+        "transport": "SX wire format (text/sx)",
+    }