Dynamic IO proxy: derive proxied primitives from component io_refs

Replace hardcoded IO primitive lists on both client and server with
data-driven registration. Page registry entries carry :io-deps (list
of IO primitive names) instead of :has-io boolean. Client registers
proxied IO on demand per page via registerIoDeps(). Server builds
allowlist from component analysis.

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

shared/sx/pages.py

@@ -555,11 +555,13 @@ def mount_io_endpoint(app: Any, service_name: str) -> None:
     from .jinja_bridge import _get_request_context
     from .parser import serialize
 
-    # Allowlist of IO primitives + page helpers the client may call
-    _ALLOWED_IO = {
-        "highlight", "current-user", "request-arg", "request-path",
-        "htmx-request?", "app-url", "asset-url", "config",
-    }
+    # Build allowlist from all component IO refs across this service
+    from .jinja_bridge import _COMPONENT_ENV
+    from .types import Component as _Comp
+    _ALLOWED_IO: set[str] = set()
+    for _val in _COMPONENT_ENV.values():
+        if isinstance(_val, _Comp) and _val.io_refs:
+            _ALLOWED_IO.update(_val.io_refs)
 
     async def io_proxy(name: str) -> Any:
         if name not in _ALLOWED_IO:
@@ -607,4 +609,4 @@ def mount_io_endpoint(app: Any, service_name: str) -> None:
         view_func=io_proxy,
         methods=["GET", "POST"],
     )
-    logger.info("Mounted IO proxy endpoint for %s at /sx/io/<name>", service_name)
+    logger.info("Mounted IO proxy for %s: %s", service_name, sorted(_ALLOWED_IO))