Phase 5: async IO rendering — components call IO primitives client-side

Wire async rendering into client-side routing: pages whose component
trees reference IO primitives (highlight, current-user, etc.) now
render client-side via Promise-aware asyncRenderToDom. IO calls proxy
through /sx/io/<name> endpoint, which falls back to page helpers.

- Add has-io flag to page registry entries (helpers.py)
- Remove IO purity filter — include IO-dependent components in bundles
- Extend try-client-route with 4 paths: pure, data, IO, data+IO
- Convert tryAsyncEvalContent to callback style, add platform mapping
- IO proxy falls back to page helpers (highlight works via proxy)
- Demo page: /isomorphism/async-io with inline highlight calls

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

shared/sx/jinja_bridge.py

@@ -349,23 +349,15 @@ def components_for_page(page_sx: str, service: str | None = None) -> tuple[str,
 
     needed = components_needed(page_sx, _COMPONENT_ENV)
 
-    # Include deps for :data pages whose component trees are fully pure
-    # (no IO refs). Pages with IO deps must render server-side.
+    # Include deps for all :data pages so the client can render them.
+    # Pages with IO deps use the async render path (Phase 5) — the IO
+    # primitives are proxied via /sx/io/<name>.
     if service:
         from .pages import get_all_pages
         for page_def in get_all_pages(service).values():
             if page_def.data_expr is not None and page_def.content_expr is not None:
                 content_src = serialize(page_def.content_expr)
-                data_deps = components_needed(content_src, _COMPONENT_ENV)
-                # Check if any dep component has IO refs
-                has_io = False
-                for dep_name in data_deps:
-                    comp = _COMPONENT_ENV.get(dep_name)
-                    if isinstance(comp, Component) and comp.io_refs:
-                        has_io = True
-                        break
-                if not has_io:
-                    needed |= data_deps
+                needed |= components_needed(content_src, _COMPONENT_ENV)
 
     if not needed:
         return "", ""
@@ -416,13 +408,7 @@ def css_classes_for_page(page_sx: str, service: str | None = None) -> set[str]:
         for page_def in get_all_pages(service).values():
             if page_def.data_expr is not None and page_def.content_expr is not None:
                 content_src = serialize(page_def.content_expr)
-                data_deps = components_needed(content_src, _COMPONENT_ENV)
-                has_io = any(
-                    isinstance(_COMPONENT_ENV.get(d), Component) and _COMPONENT_ENV.get(d).io_refs
-                    for d in data_deps
-                )
-                if not has_io:
-                    needed |= data_deps
+                needed |= components_needed(content_src, _COMPONENT_ENV)
     classes: set[str] = set()
 
     for key, val in _COMPONENT_ENV.items():