fix: restart mic capture when a call app reconfigures the input device

[jayfrid-bot]

The bug

When another process takes the microphone with voice processing — FaceTime, Zoom, any call app — macOS reconfigures the input device, and the AVAudioEngine driving the mic tap stops delivering buffers. Silently: no error, no failed write, nothing in the log. The mic track just ends while the system track keeps recording.

Real-world repro that led me here: a 19-minute FaceTime call recorded a 1.7-second mic.caf and a full-length system.caf. The call connected ~2s into the session and killed the mic capture; the transcript came out all "them", no "me". Since recording calls is presumably quill's core use case, this seemed worth fixing properly.

The fix

MicRecorder now subscribes to AVAudioEngineConfigurationChange and, after a 0.5s debounce (reconfiguration storms post several notifications back-to-back), rebuilds the engine and re-attaches the tap to the same open AVAudioFile:

• The dead span is padded with zeroed frames so the track stays wall-clock true and transcript timestamps don't drift relative to the system track.
• The restart path records raw (no voice processing) — during a call the call app owns echo cancellation, and re-engaging VP mid-call is what causes fights over the device in the first place.
• The tap converts through the file's original processing format, so a device that comes back at a different sample rate (AirPods switching to their call profile) still writes cleanly — the rate-mismatched case goes through the block-based AVAudioConverter API since the one-shot convenience only handles equal rates.
• A failed restart (device mid-reconfigure) retries every 2s for the rest of the session.

Verification

Tested on a live FaceTime call on macOS 15 / Apple Silicon: the log shows capture restarting on both the call-start and call-end reconfigurations, and a 39s test session produced a 36s mic track (the ~3s being the two debounce/re-attach windows, silence-padded) with speech correctly transcribed and speaker-tagged on both sides of the call boundary:

mic: input device reconfigured (call app?) — restarting capture
mic: input device reconfigured (call app?) — restarting capture
○ stopped · 0:39 · …/2026.07.28-1243

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[dremnik]

Appreciate the PR! will test this and merge later today