feat(audio): forward capture-event sink to recording://level/device (T7.3)

start_recording now creates the EventSink alongside the existing frame
channel and forwards Level/DeviceChanged onto a small fire-and-forget
thread that emits "recording://level" and "recording://device".

src-tauri/src/commands.rs

@@ -222,8 +222,44 @@ pub async fn start_recording(
 
     // Bounded so a slow/stalled transcription worker can never back up the capture thread.
     let (frame_tx, frame_rx) = std::sync::mpsc::sync_channel::<Vec<f32>>(8);
+    // Level updates + device-change notices (FR-CAP-5/6); low-volume, forwarded to events below.
+    let (event_tx, event_rx) = std::sync::mpsc::sync_channel::<crate::audio::CaptureEvent>(8);
     let capture = WasapiCapture
-        .start(&wav_path, frame_tx)
+        .start(&wav_path, frame_tx, event_tx)
+        .map_err(|e| WaError::new("audio", e.to_string()))?;
+
+    // Fire-and-forget: exits on its own once `event_tx` drops at capture stop;
+    // nothing downstream needs to join it.
+    let app_for_capture_events = app.clone();
+    let meeting_id_for_capture_events = meeting_id.clone();
+    std::thread::Builder::new()
+        .name("wa-capture-events".into())
+        .spawn(move || {
+            for event in event_rx {
+                match event {
+                    crate::audio::CaptureEvent::Level(level) => {
+                        let _ = app_for_capture_events.emit(
+                            "recording://level",
+                            serde_json::json!({
+                                "meetingId": meeting_id_for_capture_events,
+                                "rms": level.rms,
+                                "peak": level.peak,
+                            }),
+                        );
+                    }
+                    crate::audio::CaptureEvent::DeviceChanged { recovered, message } => {
+                        let _ = app_for_capture_events.emit(
+                            "recording://device",
+                            serde_json::json!({
+                                "meetingId": meeting_id_for_capture_events,
+                                "recovered": recovered,
+                                "message": message,
+                            }),
+                        );
+                    }
+                }
+            }
+        })
         .map_err(|e| WaError::new("audio", e.to_string()))?;
 
     let segments: Arc<StdMutex<Vec<TranscriptSegment>>> = Arc::new(StdMutex::new(Vec::new()));