feat(lotus): io.lotus.set_audio_output — host-driven output device switch (#119)

The embed hides Element Call's footer, so its own output picker is out of
reach; the host's call bar now sends io.lotus.set_audio_output { deviceId }
and the fork applies it via mediaDevices.audioOutput.select(), answering
with io.lotus.audio_output_state { deviceId } on every change.

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

src/lotus/lotusActions.test.ts

@@ -26,6 +26,7 @@ describe("LotusWidgetActions", () => {
       LotusWidgetActions.SetQuality,
       LotusWidgetActions.Decorations,
       LotusWidgetActions.SetDeafen,
+      LotusWidgetActions.SetAudioOutput,
     ];
 
     expect(new Set(LOTUS_TO_WIDGET_ACTIONS)).toEqual(new Set(expectedToWidget));

src/lotus/lotusActions.ts

@@ -52,6 +52,10 @@ export enum LotusWidgetActions {
    * disconnect or in-call teardown, whichever comes first.
    */
   CallSummary = "io.lotus.call_summary",
+  /** toWidget: select the audio output device `{ deviceId }` (#119). */
+  SetAudioOutput = "io.lotus.set_audio_output",
+  /** fromWidget: the currently selected output `{ deviceId }` (#119). */
+  AudioOutputState = "io.lotus.audio_output_state",
 }
 
 /** toWidget Lotus actions that must be allow-listed in `initializeWidget`. */
@@ -61,4 +65,5 @@ export const LOTUS_TO_WIDGET_ACTIONS: LotusWidgetActions[] = [
   LotusWidgetActions.SetQuality,
   LotusWidgetActions.Decorations,
   LotusWidgetActions.SetDeafen,
+  LotusWidgetActions.SetAudioOutput,
 ];

src/lotus/lotusAudioOutput.ts

@@ -0,0 +1,46 @@
+/*
+Copyright 2026 Lotus Guild
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { type IWidgetApiRequest } from "matrix-widget-api";
+import { logger } from "matrix-js-sdk/lib/logger";
+
+import { type MediaDevices } from "../state/MediaDevices";
+import { widget } from "../widget";
+import { LotusWidgetActions } from "./lotusActions";
+import { lotusSendToHost } from "./lotusWidget";
+
+/**
+ * [Gitea #119] Let the host switch the audio output device (headset ↔
+ * speakers) from its own call bar: `io.lotus.set_audio_output { deviceId }`
+ * selects the output; the fork answers each change (and the initial state)
+ * with `io.lotus.audio_output_state { deviceId, available: [{id,label}] }`.
+ * No effect unless the host sends the action. Returns a teardown function.
+ */
+export function startLotusAudioOutput(mediaDevices: MediaDevices): () => void {
+  const w = widget;
+  if (!w) return () => undefined;
+
+  const handler = (ev: CustomEvent<IWidgetApiRequest>): void => {
+    w.api.transport.reply(ev.detail, {});
+    const data = ev.detail.data as { deviceId?: string } | undefined;
+    if (typeof data?.deviceId !== "string") return;
+    logger.debug(`[lotus] set_audio_output: ${data.deviceId}`);
+    mediaDevices.audioOutput.select(data.deviceId);
+  };
+  w.lazyActions.on(LotusWidgetActions.SetAudioOutput, handler);
+
+  const sub = mediaDevices.audioOutput.selected$.subscribe((selected) => {
+    lotusSendToHost(LotusWidgetActions.AudioOutputState, {
+      deviceId: selected?.id ?? null,
+    });
+  });
+
+  return () => {
+    sub.unsubscribe();
+    w.lazyActions.off(LotusWidgetActions.SetAudioOutput, handler);
+  };
+}

src/room/InCallView.tsx

@@ -36,6 +36,7 @@ import { startLotusQuality } from "../lotus/lotusQuality";
 import { startLotusDecorations } from "../lotus/lotusDecorations";
 import { startLotusDenoise } from "../lotus/lotusDenoise";
 import { startLotusCallSummary } from "../lotus/lotusCallSummary";
+import { startLotusAudioOutput } from "../lotus/lotusAudioOutput";
 import { startLotusDeafen } from "../lotus/lotusDeafen";
 import styles from "./InCallView.module.css";
 import { GridTile } from "../tile/GridTile";
@@ -315,6 +316,12 @@ export const InCallView: FC<InCallViewProps> = ({
   // audio (and optionally screenshare audio) at the LiveKit source. No-op
   // unless the host sends the action.
   useEffect(() => startLotusDeafen(), []);
+  // [lotus #119] Let the host pick the audio output device from its call bar.
+  const lotusMediaDevices = useMediaDevices();
+  useEffect(
+    () => startLotusAudioOutput(lotusMediaDevices),
+    [lotusMediaDevices],
+  );
 
   const fatalCallError = useBehavior(vm.fatalError$);
   // Stop the rendering and throw for the error boundary