Add federation/ActivityPub models, contracts, and services

Phase 0+1 of ActivityPub integration:
- 6 ORM models (ActorProfile, APActivity, APFollower, APInboxItem, APAnchor, IPFSPin)
- FederationService protocol + SqlFederationService implementation + stub
- 4 DTOs (ActorProfileDTO, APActivityDTO, APFollowerDTO, APAnchorDTO)
- Registry slot for federation service
- Alembic migration for federation tables
- IPFS async client (httpx-based)
- HTTP Signatures (RSA-2048 sign/verify)
- login_url() now uses AUTH_APP env var for flexible auth routing

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

contracts/dtos.py

@@ -134,3 +134,56 @@ class CartSummaryDTO:
     items: list[CartItemDTO] = field(default_factory=list)
     ticket_count: int = 0
     ticket_total: Decimal = Decimal("0")
+
+
+# ---------------------------------------------------------------------------
+# Federation / ActivityPub domain
+# ---------------------------------------------------------------------------
+
+@dataclass(frozen=True, slots=True)
+class ActorProfileDTO:
+    id: int
+    user_id: int
+    preferred_username: str
+    public_key_pem: str
+    display_name: str | None = None
+    summary: str | None = None
+    inbox_url: str | None = None
+    outbox_url: str | None = None
+    created_at: datetime | None = None
+
+
+@dataclass(frozen=True, slots=True)
+class APActivityDTO:
+    id: int
+    activity_id: str
+    activity_type: str
+    actor_profile_id: int
+    object_type: str | None = None
+    object_data: dict | None = None
+    published: datetime | None = None
+    is_local: bool = True
+    source_type: str | None = None
+    source_id: int | None = None
+    ipfs_cid: str | None = None
+
+
+@dataclass(frozen=True, slots=True)
+class APFollowerDTO:
+    id: int
+    actor_profile_id: int
+    follower_acct: str
+    follower_inbox: str
+    follower_actor_url: str
+    created_at: datetime | None = None
+
+
+@dataclass(frozen=True, slots=True)
+class APAnchorDTO:
+    id: int
+    merkle_root: str
+    activity_count: int = 0
+    tree_ipfs_cid: str | None = None
+    ots_proof_cid: str | None = None
+    confirmed_at: datetime | None = None
+    bitcoin_txid: str | None = None

contracts/protocols.py

@@ -19,6 +19,9 @@ from .dtos import (
     ProductDTO,
     CartItemDTO,
     CartSummaryDTO,
+    ActorProfileDTO,
+    APActivityDTO,
+    APFollowerDTO,
 )
 
 
@@ -162,3 +165,67 @@ class CartService(Protocol):
     async def adopt_cart_for_user(
         self, session: AsyncSession, user_id: int, session_id: str,
     ) -> None: ...
+
+
+@runtime_checkable
+class FederationService(Protocol):
+    # -- Actor management -----------------------------------------------------
+    async def get_actor_by_username(
+        self, session: AsyncSession, username: str,
+    ) -> ActorProfileDTO | None: ...
+
+    async def get_actor_by_user_id(
+        self, session: AsyncSession, user_id: int,
+    ) -> ActorProfileDTO | None: ...
+
+    async def create_actor(
+        self, session: AsyncSession, user_id: int, preferred_username: str,
+        display_name: str | None = None, summary: str | None = None,
+    ) -> ActorProfileDTO: ...
+
+    async def username_available(
+        self, session: AsyncSession, username: str,
+    ) -> bool: ...
+
+    # -- Publishing (core cross-domain API) -----------------------------------
+    async def publish_activity(
+        self, session: AsyncSession, *,
+        actor_user_id: int,
+        activity_type: str,
+        object_type: str,
+        object_data: dict,
+        source_type: str | None = None,
+        source_id: int | None = None,
+    ) -> APActivityDTO: ...
+
+    # -- Queries --------------------------------------------------------------
+    async def get_activity(
+        self, session: AsyncSession, activity_id: str,
+    ) -> APActivityDTO | None: ...
+
+    async def get_outbox(
+        self, session: AsyncSession, username: str,
+        page: int = 1, per_page: int = 20,
+    ) -> tuple[list[APActivityDTO], int]: ...
+
+    async def get_activity_for_source(
+        self, session: AsyncSession, source_type: str, source_id: int,
+    ) -> APActivityDTO | None: ...
+
+    # -- Followers ------------------------------------------------------------
+    async def get_followers(
+        self, session: AsyncSession, username: str,
+    ) -> list[APFollowerDTO]: ...
+
+    async def add_follower(
+        self, session: AsyncSession, username: str,
+        follower_acct: str, follower_inbox: str, follower_actor_url: str,
+        follower_public_key: str | None = None,
+    ) -> APFollowerDTO: ...
+
+    async def remove_follower(
+        self, session: AsyncSession, username: str, follower_acct: str,
+    ) -> bool: ...
+
+    # -- Stats ----------------------------------------------------------------
+    async def get_stats(self, session: AsyncSession) -> dict: ...