mypy 2.4 (native parser by default) flags _jwt_username_var.set(user.username)
in agent/mcp/__init__.py: with the legacy `username = Column(String)`
declaration, instance access is typed Column[str], not str. Migrate the
column to the Mapped/mapped_column style already used by token_version and
last_login in the same table, with an explicit nullable=True so the schema
stays identical to the former Column(String) declaration.
9887e3d5d7