CI mypy caught what my local environment couldn't (Python 3.14 has no
compatible numpy stub for the project's python_version=3.11 mypy target,
so mypy couldn't run locally at all):
slot_manager.py:353: error: Incompatible types in assignment
(expression has type "str", variable has type "Timestamp")
slot_manager.py:368: error: Incompatible return value type
(got "Timestamp", expected "str | None")
Reassigning `last_data_timestamp` from a Timestamp to its strftime() string
trips mypy's inference (it fixes an unannotated local's type from its first
assignment). Split into a separate `last_data_timestamp_str` for the string
form instead of reusing the name.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
ed666c260d