fix(lotus): revert to the default output sink when the selected device disappears

Fixes #27

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/useAudioContext.tsx

@@ -6,7 +6,7 @@ Please see LICENSE in the repository root for full details.
 */
 
 import { logger } from "matrix-js-sdk/lib/logger";
-import { useState, useEffect } from "react";
+import { useState, useEffect, useRef } from "react";
 import { useObservableEagerState } from "observable-hooks";
 
 import {
@@ -172,13 +172,22 @@ export function useAudioContext<S extends string>(
     useMediaDevices().audioOutput.selected$,
   )?.id;
   const { controlledAudioDevices } = useUrlParams();
+  // [lotus] Tracks whether audioOutputId has ever resolved to a real device,
+  // so we can tell "MediaDevices hasn't resolved yet" (skip) apart from "the
+  // previously selected output device just disappeared" (revert to default,
+  // #27) — both present as audioOutputId === undefined.
+  const outputHasResolved = useRef(false);
 
   // Update the sink ID whenever we change devices.
   useEffect(() => {
+    if (typeof audioOutputId === "string") outputHasResolved.current = true;
+    if (
+      !audioContext ||
+      !("setSinkId" in audioContext) ||
+      controlledAudioDevices
+    )
+      return;
     if (
-      audioContext &&
-      "setSinkId" in audioContext &&
-      !controlledAudioDevices &&
       // Skip until a device is actually selected. audioOutputId is undefined
       // before MediaDevices resolves (e.g. on the Tauri desktop webview, where
       // the selected$ observable emits undefined first); setSinkId(undefined)
@@ -191,6 +200,15 @@ export function useAudioContext<S extends string>(
       audioContext.setSinkId(audioOutputId).catch((ex) => {
         logger.warn("Unable to change sink for audio context", ex);
       });
+    } else if (outputHasResolved.current) {
+      // [lotus] The previously selected output device disappeared (selected$
+      // re-emits undefined once devices have already resolved), not the
+      // pre-resolution case above. Revert to the default sink instead of
+      // leaving the context pinned to a now-nonexistent device (#27).
+      // @ts-expect-error - setSinkId doesn't exist yet in types, maybe because it's not supported everywhere.
+      audioContext.setSinkId("").catch((ex) => {
+        logger.warn("Unable to revert sink for audio context", ex);
+      });
     }
   }, [audioContext, audioOutputId, controlledAudioDevices]);
   const { pan: earpiecePan, volume: earpieceVolume } = useEarpieceAudioConfig();