/voice: second concurrent session fails with "No audio detected from microphone"

Summary

/voice enables voice input (push-to-talk via hold-space). When voice
input is enabled in two Claude Code sessions on the same machine, holding
space to speak in the second session fails with:

No audio detected from microphone. Check that the correct input device is selected and …

The first session captures audio fine. Disabling /voice in the first
session lets the second session capture audio. This looks like an
exclusive lock on the input device held by whichever session grabbed it
first.

Repro

1. Open two Claude Code sessions in separate terminals on the same machine.
2. In session A, run /voice to enable voice input. Hold space and

speak — works.

1. In session B, run /voice to enable voice input. Hold space and speak.
2. Session B shows "No audio detected from microphone..." at the bottom

while session A continues to capture audio normally.

Expected

Either:

• Both sessions can capture audio (shared mic access), OR
• Session B surfaces a clear "microphone in use by another Claude Code

session" message instead of a generic "no audio detected" error.

Actual

Session B shows the generic "No audio detected from microphone. Check that
the correct input device is selected..." error, which misleads the user
into checking device settings rather than other sessions.

Environment

• Claude Code v2.1.139
• Platform: macOS (Darwin 25.3.0)
• Claude Code model in use: Opus 4.7 (1M context)
• Two concurrent sessions in separate terminals, both with /voice enabled

Notes

Possibly related (different symptoms, not duplicates): #30293, #38918, #48450.