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>

contracts/protocols.py

@@ -0,0 +1,95 @@
+"""Protocol classes defining each domain's service interface.
+
+All cross-domain callers program against these Protocols.  Concrete
+implementations (Sql*Service) and no-op stubs both satisfy them.
+"""
+from __future__ import annotations
+
+from typing import Protocol, runtime_checkable
+
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from .dtos import (
+    PostDTO,
+    CalendarDTO,
+    CalendarEntryDTO,
+    MarketPlaceDTO,
+    ProductDTO,
+    CartItemDTO,
+    CartSummaryDTO,
+)
+
+
+@runtime_checkable
+class BlogService(Protocol):
+    async def get_post_by_slug(self, session: AsyncSession, slug: str) -> PostDTO | None: ...
+    async def get_post_by_id(self, session: AsyncSession, id: int) -> PostDTO | None: ...
+    async def get_posts_by_ids(self, session: AsyncSession, ids: list[int]) -> list[PostDTO]: ...
+
+
+@runtime_checkable
+class CalendarService(Protocol):
+    async def calendars_for_container(
+        self, session: AsyncSession, container_type: str, container_id: int,
+    ) -> list[CalendarDTO]: ...
+
+    async def pending_entries(
+        self, session: AsyncSession, *, user_id: int | None, session_id: str | None,
+    ) -> list[CalendarEntryDTO]: ...
+
+    async def entries_for_page(
+        self, session: AsyncSession, page_id: int, *, user_id: int | None, session_id: str | None,
+    ) -> list[CalendarEntryDTO]: ...
+
+    async def entry_by_id(self, session: AsyncSession, entry_id: int) -> CalendarEntryDTO | None: ...
+
+    async def associated_entries(
+        self, session: AsyncSession, content_type: str, content_id: int, page: int,
+    ) -> tuple[list[CalendarEntryDTO], bool]: ...
+
+    async def toggle_entry_post(
+        self, session: AsyncSession, entry_id: int, content_type: str, content_id: int,
+    ) -> bool: ...
+
+    async def adopt_entries_for_user(
+        self, session: AsyncSession, user_id: int, session_id: str,
+    ) -> None: ...
+
+    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: ...
+
+    async def confirm_entries_for_order(
+        self, session: AsyncSession, order_id: int, user_id: int | None,
+        session_id: str | None,
+    ) -> None: ...
+
+    async def get_entries_for_order(
+        self, session: AsyncSession, order_id: int,
+    ) -> list[CalendarEntryDTO]: ...
+
+
+@runtime_checkable
+class MarketService(Protocol):
+    async def marketplaces_for_container(
+        self, session: AsyncSession, container_type: str, container_id: int,
+    ) -> list[MarketPlaceDTO]: ...
+
+    async def product_by_id(self, session: AsyncSession, product_id: int) -> ProductDTO | None: ...
+
+
+@runtime_checkable
+class CartService(Protocol):
+    async def cart_summary(
+        self, session: AsyncSession, *, user_id: int | None, session_id: str | None,
+        page_slug: str | None = None,
+    ) -> CartSummaryDTO: ...
+
+    async def cart_items(
+        self, session: AsyncSession, *, user_id: int | None, session_id: str | None,
+    ) -> list[CartItemDTO]: ...
+
+    async def adopt_cart_for_user(
+        self, session: AsyncSession, user_id: int, session_id: str,
+    ) -> None: ...