Domain isolation: typed contracts, service registry, and composable wiring

Add typed service contracts (Protocols + frozen DTOs) in shared/contracts/
for cross-domain communication. Each domain exposes a service interface
(BlogService, CalendarService, MarketService, CartService) backed by SQL
implementations in shared/services/. A singleton registry with has() guards
enables composable startup — apps register their own domain service and
stubs for absent domains.

Absorbs glue layer: navigation, relationships, event handlers (login,
container, order) now live in shared/ with has()-guarded service calls.
Factory gains domain_services_fn parameter for per-app service registration.

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

infrastructure/factory.py

@@ -42,6 +42,7 @@ def create_base_app(
     *,
     context_fn: Callable[[], Awaitable[dict]] | None = None,
     before_request_fns: Sequence[Callable[[], Awaitable[None]]] | None = None,
+    domain_services_fn: Callable[[], None] | None = None,
 ) -> Quart:
     """
     Create a Quart app with shared infrastructure.
@@ -57,7 +58,13 @@ def create_base_app(
         If not provided, a minimal default context is used.
     before_request_fns:
         Extra before-request hooks (e.g. cart_loader for the cart app).
+    domain_services_fn:
+        Callable that registers domain services on the shared registry.
+        Each app provides its own — registering real impls for owned
+        domains and stubs (or real impls) for others.
     """
+    if domain_services_fn is not None:
+        domain_services_fn()
     app = Quart(
         name,
         static_folder=STATIC_DIR,
@@ -144,11 +151,8 @@ def create_base_app(
     # --- startup ---
     @app.before_serving
     async def _startup():
-        try:
-            from glue.setup import register_glue_handlers
-            register_glue_handlers()
-        except ImportError:
-            pass  # glue submodule not present in this build context
+        from shared.events.handlers import register_shared_handlers
+        register_shared_handlers()
         await init_config()
         print(pretty())
         await _event_processor.start()