Summary

• prevent macOS app crash when Voice Wake starts without a usable default audio input device
• add CoreAudio preflight for default input availability before installing AVAudioEngine tap
• keep failure in the recoverable runtime path (log + stop), avoiding SIGABRT process termination

Bug

On Macs with no usable input device (common on Mac mini/headless setups), enabling Voice Wake can crash:

• AVAudioNode.installTapOnBus throws Objective-C exception
• exception crosses into Swift runtime and aborts the app (SIGABRT)

Root Cause

VoiceWakeRuntime.start(with:) proceeded to installTap without verifying that the default input device is both present and input-capable/alive.

Changes

1. AudioInputDeviceObserver

• added hasUsableDefaultInputDevice()
• added inputAvailabilitySummary() for diagnostics
• added private helper for default UID vs alive input UID matching

2. VoiceWakeRuntime.start(with:)

• added startup guard using AudioInputDeviceObserver.hasUsableDefaultInputDevice() before installing tap
• throws normal NSError (with input summary) and exits via existing catch/stop flow

3. Tests

• added AudioInputDeviceObserverTests covering:
  • missing default UID
  • default UID not alive/input-capable
  • default UID valid/alive

Validation

• swift test --filter AudioInputDeviceObserverTests
• swift test --filter VoiceWakeRuntimeTests

Fixes

• Fixes macOS app crashes when opening VoiceWake tab (2026.2.14) #17484
• Fixes [Bug]: macOS app crashes (SIGABRT) when enabling Microphone / Voice Wake on Mac mini (no input mic) — AVAudioNode installTapOnBus throws #16418
• Fixes macOS App crashes on launch when no audio input device is available (VoiceWakeRuntime) #16118
• Fixes macOS app crashes on launch when no audio input device connected (VoiceWakeRuntime) #15740
• Fixes Mac app: SIGABRT crash when no audio input device available (voice wake) #12169