feat(voice): mic test with loopback in voice settings

The level meter only measured a stream a call had already opened, so settings
offered no way to check a mic before joining — the panel said as much.

Add startMicTest/stopMicTest on AudioManager: the processed input bus is
routed to the master output through a dedicated gain node, so the loopback can
be disconnected precisely. Settings had deliberately never opened the mic
itself; a mic test cannot honour that, so the test hands the mic back when it
stops.

Releasing needs two independent guards, because the user may join a call
mid-test: AudioManager only stops the exact stream it opened (identity check,
not a flag), and the caller must consent — the UI reads the call state, which
AudioManager cannot, as it does not import stores. Unmounting mid-test tears
the loopback down too.

packages/web/src/audio/AudioManager.ts

@@ -32,6 +32,10 @@ export class AudioManager {
   private rnnoiseReady = false;
   private keepAliveOscillator: OscillatorNode | null = null;
 
+  // Mic test (settings → Voice). See startMicTest().
+  private micTestGain: GainNode | null = null;
+  private micTestStream: MediaStream | null = null;
+
   // Cached `getUserMedia` denial. After a NotAllowedError, subsequent
   // `setInputDevice` calls (e.g. `useLiveKit.syncMic` racing the user's
   // tap on a denial prompt) re-throw the cached error WITHOUT issuing a
@@ -567,6 +571,65 @@ export class AudioManager {
     osc.stop(now + 0.45);
   }
 
+  /**
+   * Mic test: routes the processed input bus to the speakers so the user hears
+   * themselves, outside of any call.
+   *
+   * Settings deliberately never opened the mic on their own — the level meter
+   * only measures a stream that a call had already established. A mic test
+   * cannot honour that, so this is the one path that opens it, and
+   * `stopMicTest` hands it back rather than leaving the mic indicator lit.
+   *
+   * Returns false when the mic could not be opened (denied, unplugged).
+   */
+  async startMicTest(): Promise<boolean> {
+    if (this.micTestGain) return true;
+    const ctx = this.ensureContext();
+    await this.resumeContext();
+
+    const hadStream = this.hasActiveStream();
+    if (!hadStream) {
+      const stream = await this.setInputDevice(this.currentInputDeviceId);
+      if (!stream) return false;
+      // Remember the exact stream we opened, so stopMicTest only ever stops
+      // that one — never a stream something else established meanwhile.
+      this.micTestStream = this.currentStream;
+    }
+
+    this.micTestGain = ctx.createGain();
+    this.inputGain!.connect(this.micTestGain);
+    this.micTestGain.connect(this.getMasterOutput());
+    return true;
+  }
+
+  /**
+   * Tears down the loopback.
+   *
+   * @param allowRelease Whether the mic may be handed back. Only the caller
+   *   knows whether a call has started since the test began — AudioManager
+   *   does not read stores — so releasing needs its consent as well as our own
+   *   record that this test is what opened the stream.
+   */
+  stopMicTest(allowRelease: boolean): void {
+    if (!this.micTestGain) return;
+    try { this.inputGain?.disconnect(this.micTestGain); } catch { /* graph already torn down */ }
+    try { this.micTestGain.disconnect(); } catch { /* already detached */ }
+    this.micTestGain = null;
+
+    if (allowRelease && this.micTestStream && this.currentStream === this.micTestStream) {
+      // Detach listeners before stopping (see `_setInputDeviceImpl`).
+      const tracks = this.currentStream.getTracks();
+      tracks.forEach(t => { t.onended = null; });
+      tracks.forEach(t => t.stop());
+      this.currentStream = null;
+    }
+    this.micTestStream = null;
+  }
+
+  isMicTestActive(): boolean {
+    return this.micTestGain !== null;
+  }
+
   getContext(): AudioContext | null {
     return this.ctx;
   }

packages/web/src/components/modals/settingsPanels/AudioInputSection.tsx

@@ -20,6 +20,8 @@ export function AudioInputSection() {
   // then join voice and expect the meter / resolved-default hint to come
   // alive without reopening the panel.
   const [audioCtxGen, setAudioCtxGen] = useState(0);
+  const [micTesting, setMicTesting] = useState(false);
+  const [micTestError, setMicTestError] = useState('');
   const dropdownRef = useRef<HTMLDivElement>(null);
   const animFrameRef = useRef<number>(0);
 
@@ -77,7 +79,39 @@ export function AudioInputSection() {
       stopped = true;
       if (animFrameRef.current) cancelAnimationFrame(animFrameRef.current);
     };
-  }, [permState, audioCtxGen]);
+  }, [permState, audioCtxGen, micTesting]);
+
+  // Subscribed (not a one-off getState) so the hint text below tracks the call
+  // state live. The release decision itself reads getState() at the moment of
+  // stopping, which is when it must be accurate.
+  const isLiveKitConnected = useVoiceStore((s) => s.isLiveKitConnected);
+
+  const toggleMicTest = async () => {
+    const am = AudioManager.getInstance();
+    if (micTesting) {
+      am.stopMicTest(!useVoiceStore.getState().isLiveKitConnected);
+      setMicTesting(false);
+      return;
+    }
+    setMicTestError('');
+    const ok = await am.startMicTest();
+    if (!ok) {
+      setMicTestError('Could not open the microphone. Check the device and its permission.');
+      return;
+    }
+    setMicTesting(true);
+  };
+
+  // Leaving the panel mid-test must not leave the loopback running or the mic
+  // held open.
+  useEffect(() => {
+    return () => {
+      const am = AudioManager.getInstance();
+      if (am.isMicTestActive()) {
+        am.stopMicTest(!useVoiceStore.getState().isLiveKitConnected);
+      }
+    };
+  }, []);
 
   // Track the resolved upstream deviceId for the "Currently using: X" hint.
   // Re-runs on `audioCtxGen` because the resolved-default ID is only known
@@ -213,9 +247,30 @@ export function AudioInputSection() {
               />
             ))}
           </div>
-          <div className="text-xs text-txt-tertiary mt-1.5">
-            The level meter activates once you join a voice channel.
+          <div className="flex items-center gap-3 mt-3">
+            <button
+              type="button"
+              onClick={() => void toggleMicTest()}
+              disabled={permState !== 'granted'}
+              className={`px-3 py-1.5 rounded-md text-[13px] font-medium transition-colors disabled:opacity-50 disabled:cursor-not-allowed ${
+                micTesting
+                  ? 'bg-interactive-muted text-txt-primary hover:brightness-110'
+                  : 'bg-accent-primary text-white hover:brightness-110'
+              }`}
+            >
+              {micTesting ? 'Stop Testing' : "Let's Check"}
+            </button>
+            <span className="text-xs text-txt-tertiary">
+              {micTesting
+                ? 'Playing your mic back to you — say something.'
+                : isLiveKitConnected
+                  ? 'The level meter is live while you are in a call.'
+                  : 'Test your mic without joining a call.'}
+            </span>
           </div>
+          {micTestError && (
+            <div className="text-xs text-txt-danger mt-1.5">{micTestError}</div>
+          )}
         </div>
       </div>
     </SectionShell>