input.txt is now created with CreateNew, so only one request can hold it; a
lock older than 15 s is treated as left by a dead run. The outer PowerShell
stops on any error, says why in one line, releases the lock and exits 1.
docs/testing.md names both keys Set Up Connection can add to the headset.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>