Observed live on .116 after the dedup/backoff fixes: the kiosk browser's
hot-swap auto-probe (mesh.probe-device) still interleaved its handshakes
with the listener's open sequence on the same tty every backoff window —
Linux double-opens ttys silently, both handshakes corrupted each other,
and every collision's open() DTR/RTS-reset the board again. The retry
heuristic from 5f01ec31 narrowed but couldn't close the race.
A static PORT_OPEN_LOCK now covers the listener's whole device-open
sequence and each probe attempt, so exactly one prober touches the port
at a time. With this + the settle/backoff/dedup fixes, the .116 radio
completed its first MeshCore handshake in days (node-fa161601, 8
contacts) and the session has been stable since.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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