Guard against InvalidStateError from stale BLE notifications in DeviceReader._notification_handler

[shbatm]

Fixes #64

Problem

DeviceReader._notification_handler calls self.notify_future.set_result(...) unconditionally. If the pending response future is already done — resolved by an earlier notification, or cancelled by the 5s asyncio.wait_for timeout in _async_send_command — a late or duplicate BLE notification raises asyncio.InvalidStateError inside the notification task, which surfaces as an unhandled task exception.

Seen in the wild via the hassio-bluetti-bt custom integration (v0.2.2, pinning bluetti-bt-lib==0.1.7) on Home Assistant / Python 3.14, flooding the logs:

<class 'asyncio.exceptions.InvalidStateError'>: invalid state
future: <Task finished name='Task-XXXXXX'
  coro=<DeviceReader._notification_handler() done,
  defined at .../site-packages/bluetti_bt_lib/bluetooth/device_reader.py:252>
  exception=InvalidStateError('invalid state')>

Same root cause as the traceback reported in #64 (line 280 in 0.1.6 is the same set_result call).

Fix

Guard the resolution with notify_future.done() (which also covers cancellation) and drop the stale notification with a debug log so it stays diagnosable. The guard runs before notify_response.extend(data) so a late fragment can't mutate a bytearray result already delivered to the waiter in _async_send_command.

Dropping is safe: the first response wins, and the existing consumer-side timeout already handles genuinely missed responses.

Testing

• Added test_notification_with_done_future covering both the duplicate-notification and cancelled-future (timeout) paths; it fails with InvalidStateError before the fix and passes after.
• Full suite from Dockerfile.test passes (67 tests across tests/, fields/, registers/, base_devices/, devices/).
• Changed files checked with black --target-version py310 (the remaining reformat hints in device_reader.py are on pre-existing lines, left untouched to keep the diff minimal).

No version bump included — left to the maintainer since setup.py takes the version from LIB_VERSION at release time.

🤖 Generated with Claude Code

https://claude.ai/code/session_01GcnWB3thiiJUoaHHJDS9r5

[Patrick762]

Links:
https://docs.python.org/3/library/asyncio-future.html