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>

services/stubs.py

@@ -0,0 +1,111 @@
+"""No-op stub services for absent domains.
+
+When an app starts without a particular domain, it registers the stub
+so that ``services.X.method()`` returns empty/None rather than crashing.
+"""
+from __future__ import annotations
+
+from decimal import Decimal
+
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from shared.contracts.dtos import (
+    PostDTO,
+    CalendarDTO,
+    CalendarEntryDTO,
+    MarketPlaceDTO,
+    ProductDTO,
+    CartItemDTO,
+    CartSummaryDTO,
+)
+
+
+class StubBlogService:
+    async def get_post_by_slug(self, session: AsyncSession, slug: str) -> PostDTO | None:
+        return None
+
+    async def get_post_by_id(self, session: AsyncSession, id: int) -> PostDTO | None:
+        return None
+
+    async def get_posts_by_ids(self, session: AsyncSession, ids: list[int]) -> list[PostDTO]:
+        return []
+
+
+class StubCalendarService:
+    async def calendars_for_container(
+        self, session: AsyncSession, container_type: str, container_id: int,
+    ) -> list[CalendarDTO]:
+        return []
+
+    async def pending_entries(
+        self, session: AsyncSession, *, user_id: int | None, session_id: str | None,
+    ) -> list[CalendarEntryDTO]:
+        return []
+
+    async def entries_for_page(
+        self, session: AsyncSession, page_id: int, *, user_id: int | None, session_id: str | None,
+    ) -> list[CalendarEntryDTO]:
+        return []
+
+    async def entry_by_id(self, session: AsyncSession, entry_id: int) -> CalendarEntryDTO | None:
+        return None
+
+    async def associated_entries(
+        self, session: AsyncSession, content_type: str, content_id: int, page: int,
+    ) -> tuple[list[CalendarEntryDTO], bool]:
+        return [], False
+
+    async def toggle_entry_post(
+        self, session: AsyncSession, entry_id: int, content_type: str, content_id: int,
+    ) -> bool:
+        return False
+
+    async def adopt_entries_for_user(
+        self, session: AsyncSession, user_id: int, session_id: str,
+    ) -> None:
+        pass
+
+    async def claim_entries_for_order(
+        self, session: AsyncSession, order_id: int, user_id: int | None,
+        session_id: str | None, page_post_id: int | None,
+    ) -> None:
+        pass
+
+    async def confirm_entries_for_order(
+        self, session: AsyncSession, order_id: int, user_id: int | None,
+        session_id: str | None,
+    ) -> None:
+        pass
+
+    async def get_entries_for_order(
+        self, session: AsyncSession, order_id: int,
+    ) -> list[CalendarEntryDTO]:
+        return []
+
+
+class StubMarketService:
+    async def marketplaces_for_container(
+        self, session: AsyncSession, container_type: str, container_id: int,
+    ) -> list[MarketPlaceDTO]:
+        return []
+
+    async def product_by_id(self, session: AsyncSession, product_id: int) -> ProductDTO | None:
+        return None
+
+
+class StubCartService:
+    async def cart_summary(
+        self, session: AsyncSession, *, user_id: int | None, session_id: str | None,
+        page_slug: str | None = None,
+    ) -> CartSummaryDTO:
+        return CartSummaryDTO()
+
+    async def cart_items(
+        self, session: AsyncSession, *, user_id: int | None, session_id: str | None,
+    ) -> list[CartItemDTO]:
+        return []
+
+    async def adopt_cart_for_user(
+        self, session: AsyncSession, user_id: int, session_id: str,
+    ) -> None:
+        pass