The work_sessions.agent_id column is nullable=True with ondelete=SET
NULL — deleting an agent nulls the FK on every session it ever held. The
ORM annotation lied (Mapped[UUID] non-optional), the converter papered
over the lie (typing_cast to a non-optional UUID), and the response
model rejected None outright (WorkSessionResponse.agent_id: UUID). A
session whose agent had been deleted crashed the GET endpoint with a
pydantic ValidationError instead of serializing agent_id: null.
Make the read path honest end-to-end:
- WorkSessionTable.agent_id: Mapped[UUID | None] (matches the column).
- WorkSessionResponse.agent_id: UUID | None (serializes null, no crash).
- session_to_response passes agent_id via typing_cast('UUID | None', ...)
to bridge SQLAlchemy's UUID[Any] to stdlib uuid.UUID while preserving
None-ness (the cast stays for the same mypy-plugin reason every other
field uses one; it no longer narrows away None).
WorkSessionCreate.agent_id stays UUID — at create time the claiming
agent is always known. The unused WorkSession pydantic read model is
left as-is (never materialized from a DB row). task.py:_needs_revision_dev
already None-guards ws.agent_id via to_python_uuid (returns None -> skip).
