Fix streaming demo: preserve app context across async generator yields

Quart's ASGI layer doesn't propagate request/app context into async
generator iterations. Wrap execute_page_streaming with stream_with_context
so current_app and request remain accessible after each yield.

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

shared/sx/pages.py

@@ -507,7 +507,7 @@ def mount_pages(bp: Any, service_name: str,
 
 def _mount_one_page(bp: Any, service_name: str, page_def: PageDef) -> None:
     """Mount a single PageDef as a GET route on the blueprint."""
-    from quart import make_response, Response
+    from quart import make_response, Response, stream_with_context
 
     if page_def.stream:
         # Streaming response: yields HTML chunks as IO resolves
@@ -520,9 +520,10 @@ def _mount_one_page(bp: Any, service_name: str, page_def: PageDef) -> None:
                 if hasattr(result, "status_code"):
                     return result
                 return await make_response(result, 200)
-            # Streaming response
+            # Streaming response — stream_with_context preserves app/request
+            # context across async generator yields
             gen = execute_page_streaming(current, service_name, url_params=kwargs)
-            return Response(gen, content_type="text/html; charset=utf-8")
+            return Response(stream_with_context(gen), content_type="text/html; charset=utf-8")
     else:
         # Standard non-streaming response
         async def page_view(**kwargs: Any) -> Any: