fix: reject silent microphone captures in clamshell mode

Sources/VocaMac/Models/AppState.swift

@@ -611,6 +611,14 @@ final class AppState: ObservableObject {
             return
         }
 
+        guard audioData.contains(where: { abs($0) >= 0.0001 }) else {
+            cursorOverlay.hide()
+            let message = "No microphone audio detected. If your MacBook lid is closed, select an external microphone in Settings → Audio."
+            VocaLogger.warning(.appState, message)
+            showTemporaryError(message)
+            return
+        }
+
         appStatus = .processing
 
         do {

Sources/VocaMac/Views/SettingsView.swift

@@ -652,7 +652,7 @@ struct AudioSettingsTab: View {
                         Text("\(selectedAudioDeviceDisplayName) (Unavailable)").tag(appState.selectedAudioDeviceID)
                     }
                     ForEach(audioDevices) { device in
-                        Text(audioDeviceLabel(for: device)).tag(device.id)
+                        Text(device.name).tag(device.id)
                     }
                 }
                 .onChange(of: appState.selectedAudioDeviceID) { _ in
@@ -721,10 +721,6 @@ struct AudioSettingsTab: View {
         return "VocaMac will follow macOS' system default input."
     }
 
-    private func audioDeviceLabel(for device: AudioDevice) -> String {
-        device.isDefault ? "\(device.name) (System Default)" : device.name
-    }
-
     private func refreshAudioDevices() {
         audioDevices = AudioEngine.availableInputDevices()
         syncSelectedAudioDeviceName()

Tests/VocaMacTests/AppStateRecordingTests.swift

@@ -118,6 +118,20 @@ final class AppStateRecordingTests: XCTestCase {
                       "Should return to idle when audio data is empty")
     }
 
+    func testStopRecordingWithSilentAudioShowsInputError() async {
+        let (appState, mocks) = AppState.makeTestState()
+        mocks.audioEngine.stopRecordingResult = Array(repeating: 0, count: 16_000)
+        appState.isRecording = true
+        appState.appStatus = .recording
+
+        await appState.stopRecordingAndTranscribe()
+
+        XCTAssertEqual(appState.appStatus, .error)
+        XCTAssertTrue(appState.errorMessage?.contains("external microphone") == true)
+        XCTAssertNil(mocks.whisperService.lastTranscribedAudioData)
+        XCTAssertEqual(mocks.textInjector.injectCallCount, 0)
+    }
+
     func testSelectedModelSizeDefault() {
         let (appState, _) = AppState.makeTestState()