fix: tolerate headset input startup route churn

Sources/VocaMac/Services/AudioEngine.swift

@@ -25,6 +25,8 @@ final class AudioEngine {
     private let bufferQueue = DispatchQueue(label: "com.vocamac.audio-buffer", qos: .userInteractive)
     private let lifecycleQueue = DispatchQueue(label: "com.vocamac.audio-engine.lifecycle", qos: .userInitiated)
 
+    static let startupConfigurationChangeRecoveryWindow: TimeInterval = 1.0
+
     var isCurrentlyRecording: Bool {
         lifecycleQueue.sync { _isCurrentlyRecording }
     }
@@ -129,6 +131,14 @@ final class AudioEngine {
 
             let wasRecording = self._isCurrentlyRecording
 
+            let elapsedSinceRecordingStart = Date().timeIntervalSince(self.recordingStartTime)
+            if wasRecording,
+               self.engine?.isRunning == true,
+               Self.shouldTreatAsStartupConfigurationChange(elapsedSinceRecordingStart: elapsedSinceRecordingStart) {
+                VocaLogger.info(.audioEngine, "Ignoring startup audio configuration change because the engine is still running")
+                return
+            }
+
             if wasRecording {
                 VocaLogger.warning(.audioEngine, "Configuration changed while recording — forcing stop and reset")
                 // Tear down the stale recording state
@@ -366,6 +376,17 @@ final class AudioEngine {
         }
     }
 
+    /// Returns whether a configuration notification is close enough to recording
+    /// startup to be treated as device/profile setup churn instead of a live
+    /// device interruption.
+    static func shouldTreatAsStartupConfigurationChange(
+        elapsedSinceRecordingStart: TimeInterval,
+        recoveryWindow: TimeInterval = startupConfigurationChangeRecoveryWindow
+    ) -> Bool {
+        elapsedSinceRecordingStart >= 0
+            && elapsedSinceRecordingStart <= recoveryWindow
+    }
+
     // MARK: - Audio Processing
 
     /// Whether silence detection has already fired (prevents repeated callbacks)

Tests/VocaMacTests/ServiceTests.swift

@@ -601,6 +601,21 @@ final class AudioEngineForceResetTests: XCTestCase {
 
 final class AudioEngineDeviceChangeTests: XCTestCase {
 
+    func testStartupConfigurationChangeWindow() {
+        let cases: [(elapsed: TimeInterval, expected: Bool)] = [
+            (0.10, true),
+            (AudioEngine.startupConfigurationChangeRecoveryWindow + 0.01, false),
+            (-0.01, false)
+        ]
+
+        for testCase in cases {
+            XCTAssertEqual(
+                AudioEngine.shouldTreatAsStartupConfigurationChange(elapsedSinceRecordingStart: testCase.elapsed),
+                testCase.expected
+            )
+        }
+    }
+
     func testOnAudioDeviceChangedCallbackExists() {
         // Verify the callback property can be set
         let engine = AudioEngine()