fixup docs

sdk/SdkArchitecture.md

@@ -33,18 +33,18 @@ therefore `Element Call → sdk`, never the reverse. The migration from today's
 │   per track     MediaTrack  { source kind muted$ encrypted$ stats$ attach() }│
 │                                                                              │
 │  ┌───────────────────────────┐  MediaBackend   ┌───────────────────────────┐ │
-│  │ session: MatrixRTC        │  backend/api.ts │ media backend             │ │
+│  │ session: MatrixRTC        │ media-backend/  │ media backend             │ │
-│  │                           │                 │ backend/livekit/ today,   │ │
+│  │                           │   api.ts        │ media-backend/livekit/    │ │
-│  │ js-sdk MatrixRTCSession,  │                 │ or options.backend        │ │
+│  │ js-sdk MatrixRTCSession,  │                 │ today, or options.backend │ │
 │  │   later the rust-rtc      │ prepareLocal    │                           │ │
 │  │   crate behind a bridge   │   Transport ───▶│ token service:            │ │
 │  │ memberships from room     │ delegateDelayed │   OpenID → JWT,           │ │
 │  │   state and sticky events │   Leave ───────▶│   delegation probe        │ │
 │  │ own membership, delayed   │                 │ ConnectionManager:        │ │
 │  │   leave, retries          │ mediaKeys$ ────▶│   one LiveKit room per    │ │
-│  │ discovery of the local    │                 │   transport url, local    │ │
+│  │ discovery of the local    │ mediaFor$ ─────▶│   transport url, local    │ │
-│  │   transport (homeserver)  │ mediaFor$ ─────▶│   published, remote       │ │
+│  │   transport (homeserver)  │ ◀─ tracks$,     │   published, remote       │ │
-│  │ join state machine        │ ◀────── media$  │   subscribed              │ │
+│  │ join state machine        │ encryptionError$│   subscribed              │ │
 │  │   (LocalMember)           │ local.publish,  │ Publisher: local tracks,  │ │
 │  │ transport registry        │   setPublishing▶│   upstream paused until   │ │
 │  │   (TransportMetadata)     │ ◀─ connections$ │   joined                  │ │

sdk/src/media-backend/api.ts

@@ -9,7 +9,7 @@ Please see LICENSE in the repository root for full details.
  * The seam between the session and whatever carries its media. The session
  * speaks MatrixRTC: memberships, transports as they appear in them, the
  * delayed leave. A backend speaks one media protocol and hands back the
- * media of each member. `backend/livekit/` is the one backend today.
+ * media of each member. `media-backend/livekit/` is the one backend today.
  */
 
 import { type Logger } from "matrix-js-sdk/lib/logger";
@@ -157,7 +157,12 @@ export interface MediaBackend {
   /** Every connection the backend holds. For debugging and devtool purposes.*/
   readonly connections$: Behavior<BackendConnection[]>;
 
-  /** Plays the members' audio on this device, on the connections of now and later. */
+  /**
+   * Plays the members' audio on this device: on the local transport's
+   * connection, whether it is connected yet or not, and on every connection
+   * created from then on. A connection to a remote transport that already
+   * exists keeps the device it was created with.
+   */
   setAudioOutputDeviceId(deviceId: string): Promise<void>;
 
   /**

sdk/src/media-backend/livekit/Publisher.ts

@@ -6,7 +6,6 @@ Please see LICENSE in the repository root for full details.
 */
 
 import {
-  ConnectionState as LivekitConnectionState,
   type LocalTrackPublication,
   ParticipantEvent,
   type Room as LivekitRoom,
@@ -207,13 +206,12 @@ export class Publisher {
     return [...this.room.localParticipant.trackPublications.values()];
   }
 
-  /** A room that is not connected yet takes the device from its options instead. */
+  /**
+   * Works on a room that is still connecting too: LiveKit keeps the device
+   * in the room's options and gives it to every participant that arrives.
+   */
   public async setAudioOutputDevice(deviceId: string): Promise<void> {
-    if (
+    if (this.room.getActiveDevice("audiooutput") === deviceId) return;
-      this.room.state !== LivekitConnectionState.Connected ||
-      this.room.getActiveDevice("audiooutput") === deviceId
-    )
-      return;
     await this.room.switchActiveDevice("audiooutput", deviceId);
   }
 }