fix: avoid double-closing serial transport

[eburi]

Summary

• let the serial transport own shutdown of the underlying pyserial object
• remove the direct raw serial close after StreamWriter.close()

Why

When a serial device disconnects or times out, SerialTransport.close() schedules its own async connection-lost cleanup, including flushing and closing the serial object. The integration was also immediately closing the raw pyserial object, which can leave the transport cleanup trying to flush a port that is already closed.

On Home Assistant 2026.7 this shows up as repeated log errors like:

Exception in callback SerialTransport._call_connection_lost()
serial.serialutil.PortNotOpenError: Attempting to use a port that is not open

This was observed with a CP210x-backed Meshtastic serial connection where the host kernel was also reporting cp210x ttyUSB1: failed set request 0x12 status: -110 during the same reconnect cadence.

This PR intentionally does not change the pyserial-asyncio dependency, since #161 already covers the pyserial-asyncio-fast migration.

Testing

• .venv/bin/python -m ruff check .
• .venv/bin/python -m ruff format . --check
• git diff --check

Note: full requirements.txt install was not possible in this local environment because its Python version does not satisfy the pinned Home Assistant version; the checks above were run with the repo-pinned Ruff version 0.11.8.

Summary by CodeRabbit

• Bug Fixes
  • Improved connection shutdown handling to avoid unnecessary low-level serial port closure.
  • Streamlined cleanup so disconnects rely on the standard shutdown flow, reducing the chance of lingering state issues.

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[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: e3b20db9-ee2d-493d-96b3-5811febe02d9

📥 Commits

Reviewing files that changed from the base of the PR and between 3594f35 and e6a741a.

📒 Files selected for processing (1)

• custom_components/meshtastic/aiomeshtastic/connection/serial.py

💤 Files with no reviewable changes (1)

• custom_components/meshtastic/aiomeshtastic/connection/serial.py

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📝 Walkthrough

Walkthrough

Removed an unused typing.cast import and eliminated an explicit close of the underlying serial transport in SerialConnection._disconnect, relying solely on the StreamWriter.close() call for shutdown cleanup.

Changes

Serial Disconnect Cleanup

Layer / File(s)	Summary
Remove explicit serial transport close custom_components/meshtastic/aiomeshtastic/connection/serial.py	Removed unused cast import and the explicit cast(...).serial.close() call in _disconnect, leaving StreamWriter.close() to handle shutdown.

Estimated code review effort: 1 (Trivial) | ~3 minutes

Poem

A close call removed, tidy and neat,
One less line for the writer to greet.
The stream still shuts with a graceful sigh,
No cast needed, no need to pry.
Hop, hop, hooray — cleaner code nearby! 🐇

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly matches the main change: removing the extra serial transport close during disconnect.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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