Fix handler execution: inject page helpers into handler env

component-source and handler-source are page helpers, not IO primitives.
They need to be in the handler evaluation env just like defpage evaluation.

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

shared/sx/handlers.py

@@ -127,6 +127,7 @@ async def execute_handler(
     4. Return ``SxExpr`` wire format
     """
     from .jinja_bridge import get_component_env, _get_request_context
+    from .pages import get_page_helpers
     import os
     if os.environ.get("SX_USE_REF") == "1":
         from .ref.async_eval_ref import async_eval_to_sx
@@ -139,6 +140,7 @@ async def execute_handler(
 
     # Build environment
     env = dict(get_component_env())
+    env.update(get_page_helpers(service_name))
     env.update(handler_def.closure)
 
     # Bind handler params from request args