Two small incompatibilities surfaced after rebasing dev-kg7qin-changes
onto upstream/dev in code introduced by #138:
- message_handler.py: replace two remaining Optional[str] annotations
with str | None; the Optional import was removed during typing
modernization but two annotations in this module were missed
- command_manager.py: restore # noqa: F401 guard on PUBLIC_CHANNEL_KEY_HEX
re-export so ruff auto-fix does not silently remove it (imported by core.py)
Do not merge until #138 is merged.