feat(persistence): unify ThreadMetaStore interface with user isolation and factory

Add user_id parameter to all ThreadMetaStore abstract methods. Implement
owner isolation in MemoryThreadMetaStore with _get_owned_record helper.
Add check_access to base class and memory implementation. Add
make_thread_store factory to simplify deps.py initialization. Add
memory-backend isolation tests.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/packages/harness/deerflow/persistence/thread_meta/base.py

@@ -3,12 +3,21 @@
 Implementations:
 - ThreadMetaRepository: SQL-backed (sqlite / postgres via SQLAlchemy)
 - MemoryThreadMetaStore: wraps LangGraph BaseStore (memory mode)
+
+All mutating and querying methods accept a ``user_id`` parameter with
+three-state semantics (see :mod:`deerflow.runtime.user_context`):
+
+- ``AUTO`` (default): resolve from the request-scoped contextvar.
+- Explicit ``str``: use the provided value verbatim.
+- Explicit ``None``: bypass owner filtering (migration/CLI only).
 """
 
 from __future__ import annotations
 
 import abc
 
+from deerflow.runtime.user_context import AUTO, _AutoSentinel
+
 
 class ThreadMetaStore(abc.ABC):
     @abc.abstractmethod
@@ -17,14 +26,14 @@ class ThreadMetaStore(abc.ABC):
         thread_id: str,
         *,
         assistant_id: str | None = None,
-        owner_id: str | None = None,
+        user_id: str | None | _AutoSentinel = AUTO,
         display_name: str | None = None,
         metadata: dict | None = None,
     ) -> dict:
         pass
 
     @abc.abstractmethod
-    async def get(self, thread_id: str) -> dict | None:
+    async def get(self, thread_id: str, *, user_id: str | None | _AutoSentinel = AUTO) -> dict | None:
         pass
 
     @abc.abstractmethod
@@ -35,26 +44,33 @@ class ThreadMetaStore(abc.ABC):
         status: str | None = None,
         limit: int = 100,
         offset: int = 0,
+        user_id: str | None | _AutoSentinel = AUTO,
     ) -> list[dict]:
         pass
 
     @abc.abstractmethod
-    async def update_display_name(self, thread_id: str, display_name: str) -> None:
+    async def update_display_name(self, thread_id: str, display_name: str, *, user_id: str | None | _AutoSentinel = AUTO) -> None:
         pass
 
     @abc.abstractmethod
-    async def update_status(self, thread_id: str, status: str) -> None:
+    async def update_status(self, thread_id: str, status: str, *, user_id: str | None | _AutoSentinel = AUTO) -> None:
         pass
 
     @abc.abstractmethod
-    async def update_metadata(self, thread_id: str, metadata: dict) -> None:
+    async def update_metadata(self, thread_id: str, metadata: dict, *, user_id: str | None | _AutoSentinel = AUTO) -> None:
         """Merge ``metadata`` into the thread's metadata field.
 
         Existing keys are overwritten by the new values; keys absent from
-        ``metadata`` are preserved. No-op if the thread does not exist.
+        ``metadata`` are preserved. No-op if the thread does not exist
+        or the owner check fails.
         """
         pass
 
     @abc.abstractmethod
-    async def delete(self, thread_id: str) -> None:
+    async def check_access(self, thread_id: str, user_id: str, *, require_existing: bool = False) -> bool:
+        """Check if ``user_id`` has access to ``thread_id``."""
+        pass
+
+    @abc.abstractmethod
+    async def delete(self, thread_id: str, *, user_id: str | None | _AutoSentinel = AUTO) -> None:
         pass