Merge pull request #4242 from element-hq/delayed-leave-timings

Adapt delayed leave timings when delegation is available
2026-09-10 21:55:19 +00:00 · 2026-09-09 08:19:58 +02:00
parent 00d0adc3c4 cff8766aa6
commit 61eeb8171a
18 changed files with 570 additions and 527 deletions
@@ -9,8 +9,6 @@
  "matrix_rtc_session": {
    "wait_for_key_rotation_ms": 3000,
    "membership_event_expiry_ms": 180000000,
-    "delayed_leave_event_delay_ms": 18000,
-    "delayed_leave_event_restart_ms": 4000,
    "network_error_retry_ms": 100
  }
 }
@@ -13,8 +13,6 @@
  "matrix_rtc_session": {
    "wait_for_key_rotation_ms": 3000,
    "membership_event_expiry_ms": 180000000,
-    "delayed_leave_event_delay_ms": 18000,
-    "delayed_leave_event_restart_ms": 4000,
    "network_error_retry_ms": 100
  }
 }
@@ -9,8 +9,6 @@
  "matrix_rtc_session": {
    "wait_for_key_rotation_ms": 3000,
    "membership_event_expiry_ms": 180000000,
-    "delayed_leave_event_delay_ms": 18000,
-    "delayed_leave_event_restart_ms": 4000,
    "network_error_retry_ms": 100
  },
  "posthog": {
@@ -9,8 +9,6 @@
  "matrix_rtc_session": {
    "wait_for_key_rotation_ms": 3000,
    "membership_event_expiry_ms": 180000000,
-    "delayed_leave_event_delay_ms": 18000,
-    "delayed_leave_event_restart_ms": 4000,
    "network_error_retry_ms": 100
  }
 }
@@ -24,6 +24,35 @@ export enum MatrixRTCMode {
  Matrix_2_0 = "matrix_2_0",
 }

+export interface DelayedLeaveTimings {
+  /**
+   * The delay (in milliseconds) with which delayed leave events are sent.
+   *
+   * If the server receives no keep-alives from the client for any longer than
+   * this duration, it will send the leave event, automatically removing the
+   * user from the call.
+   */
+  delay_ms?: number;
+
+  /**
+   * How frequently (in milliseconds) the client sends keep-alives to the server
+   * to restart the timer for a delayed leave event. Should be less than
+   * {@link DelayedLeaveTimings.delay_ms}.
+   */
+  restart_ms?: number;
+
+  /**
+   * The time (in milliseconds) after which we consider a delayed event restart HTTP request to have failed.
+   * Setting this to a lower value will result in more frequent retries, but then we will also give up earlier.
+   *
+   * In the presence of network packet loss (hurting TCP connections), the custom delayedEventRestartLocalTimeoutMs
+   * helps by keeping more delayed event reset candidates in flight,
+   * improving the chances of a successful reset. (its is equivalent to the js-sdk `localTimeout` configuration,
+   * but only applies to calls to the `_unstable_updateDelayedEvent` endpoint with a body of `{action:"restart"}`.)
+   */
+  restart_timeout_ms?: number;
+}
+
 export interface ConfigOptions {
  /**
   * The Posthog endpoint to which analytics data will be sent.
@@ -184,29 +213,6 @@ export interface ConfigOptions {
     */
    wait_for_key_rotation_ms?: number;

-    /**
-     * The duration (in milliseconds) after the most recent keep-alive (delayed leave event restart)
-     * that the server waits before sending the leave MatrixRTC membership event.
-     */
-    delayed_leave_event_delay_ms?: number;
-
-    /**
-     * The time (in milliseconds) after which we consider a delayed event restart http request to have failed.
-     * Setting this to a lower value will result in more frequent retries but also a higher chance of failiour.
-     *
-     * In the presence of network packet loss (hurting TCP connections), the custom delayedEventRestartLocalTimeoutMs
-     * helps by keeping more delayed event reset candidates in flight,
-     * improving the chances of a successful reset. (its is equivalent to the js-sdk `localTimeout` configuration,
-     * but only applies to calls to the `_unstable_updateDelayedEvent` endpoint with a body of `{action:"restart"}`.)
-     */
-    delayed_leave_event_restart_local_timeout_ms?: number;
-
-    /**
-     * The time interval (in milliseconds) at which the client sends membership keep-alive
-     * messages to the server by restarting the timer for the delayed leave event.
-     */
-    delayed_leave_event_restart_ms?: number;
-
    /**
     * How long we wait before retrying after a network error on any of the requests.
     */
@@ -231,9 +237,28 @@ export interface ConfigOptions {
     * Defaults to the js-sdk default (undefined). Which means that rotation will always happen.
     */
    key_rotation_participant_limit?: number;
+
+    /**
+     * Timing options for delayed leave events, which are used to remove a user
+     * from a call when they lose connection.
+     */
+    delayed_leave?: DelayedLeaveTimings;
+
+    /**
+     * Timing options for delayed leave events, in cases where the ability to
+     * send the event can be delegated to the SFU.
+     *
+     * We recommend setting {@link DelayedLeaveTimings.delay_ms} >>
+     * {@link sync_disconnect_grace_period_ms} here.
+     */
+    delegated_delayed_leave?: DelayedLeaveTimings;
  };
 }

+export interface ResolvedDelayedLeaveTimings extends DelayedLeaveTimings {
+  delay_ms: number; // Required
+}
+
 // Overrides members from ConfigOptions that are always provided by the
 // default config and are therefore non-optional.
 export interface ResolvedConfigOptions extends ConfigOptions {
@@ -257,19 +282,15 @@ export interface ResolvedConfigOptions extends ConfigOptions {
      >
    >;
  };
-  matrix_rtc_session: {
-    wait_for_key_rotation_ms?: number;
-    delayed_leave_event_delay_ms: number;
-    delayed_leave_event_restart_local_timeout_ms?: number;
-    delayed_leave_event_restart_ms?: number;
+  matrix_rtc_session: ConfigOptions["matrix_rtc_session"] & {
    network_error_retry_ms: number;
-    membership_event_expiry_ms?: number;
-    key_rotation_participant_limit?: number;
+    delayed_leave: ResolvedDelayedLeaveTimings;
+    delegated_delayed_leave: ResolvedDelayedLeaveTimings;
  };
 }

 export const DEFAULT_CONFIG: ResolvedConfigOptions = {
-  sync_disconnect_grace_period_ms: 10000,
+  sync_disconnect_grace_period_ms: 10_000,
  ssla: "https://static.element.io/legal/element-software-and-services-license-agreement-uk-1.pdf",
  media_quality: {
    video_codec: "vp8",
@@ -285,7 +306,8 @@ export const DEFAULT_CONFIG: ResolvedConfigOptions = {
    },
  },
  matrix_rtc_session: {
-    delayed_leave_event_delay_ms: 10000,
-    network_error_retry_ms: 1000,
+    network_error_retry_ms: 1_000,
+    delayed_leave: { delay_ms: 18_000, restart_ms: 4_000 },
+    delegated_delayed_leave: { delay_ms: 3_600_000, restart_ms: 300_000 },
  },
 };
@@ -148,7 +148,7 @@ describe("getSFUConfigWithOpenID", () => {
        // Verify, that the request contains the expected delay parameters
        if (
          body.delay_id === "mock_delay_id" &&
-          body.delay_timeout === 10000 &&
+          body.delay_timeout === 3600000 &&
          body.delay_cs_api_url === "https://homeserverserver.org/cs_api"
        ) {
          return {
@@ -229,7 +229,7 @@ describe("getSFUConfigWithOpenID", () => {
    expect(calls[0][0]).toStrictEqual("https://sfu.example.org/get_token");
    expect(calls[0][1]).toStrictEqual({
      // check if it uses correct delayID!
-      body: '{"room_id":"!example_room_id","slot_id":"m.call#ROOM","member":{"id":"@alice:example.org:DEVICE","claimed_user_id":"@alice:example.org","claimed_device_id":"DEVICE"},"delay_id":"mock_delay_id","delay_timeout":10000,"delay_cs_api_url":"https://matrix.homeserverserver.org"}',
+      body: '{"room_id":"!example_room_id","slot_id":"m.call#ROOM","member":{"id":"@alice:example.org:DEVICE","claimed_user_id":"@alice:example.org","claimed_device_id":"DEVICE"},"delay_id":"mock_delay_id","delay_timeout":3600000,"delay_cs_api_url":"https://matrix.homeserverserver.org"}',
      method: "POST",
      headers: {
        "Content-Type": "application/json",
@@ -239,7 +239,7 @@ describe("getSFUConfigWithOpenID", () => {
    expect(calls[1][0]).toStrictEqual("https://sfu.example.org/sfu/get");

    expect(calls[1][1]).toStrictEqual({
-      body: '{"room":"!example_room_id","device_id":"DEVICE","delay_id":"mock_delay_id","delay_timeout":10000,"delay_cs_api_url":"https://matrix.homeserverserver.org"}',
+      body: '{"room":"!example_room_id","device_id":"DEVICE","delay_id":"mock_delay_id","delay_timeout":3600000,"delay_cs_api_url":"https://matrix.homeserverserver.org"}',
      headers: {
        "Content-Type": "application/json",
      },
@@ -284,7 +284,7 @@ describe("getSFUConfigWithOpenID", () => {
    expect(calls[0][0]).toStrictEqual("https://sfu.example.org/get_token");
    expect(calls[0][1]).toStrictEqual({
      // check if it uses correct delayID!
-      body: '{"room_id":"!example_room_id","slot_id":"m.call#ROOM","member":{"id":"@alice:example.org:DEVICE","claimed_user_id":"@alice:example.org","claimed_device_id":"DEVICE"},"delay_id":"mock_delay_id","delay_timeout":10000,"delay_cs_api_url":"https://matrix.homeserverserver.org"}',
+      body: '{"room_id":"!example_room_id","slot_id":"m.call#ROOM","member":{"id":"@alice:example.org:DEVICE","claimed_user_id":"@alice:example.org","claimed_device_id":"DEVICE"},"delay_id":"mock_delay_id","delay_timeout":3600000,"delay_cs_api_url":"https://matrix.homeserverserver.org"}',
      method: "POST",
      headers: {
        "Content-Type": "application/json",
@@ -19,7 +19,7 @@ import {
 } from "../utils/errors";
 import { doNetworkOperationWithRetry } from "../utils/matrix";
 import { Config } from "../config/Config";
-import { JwtEndpointVersion } from "../state/CallViewModel/localMember/LocalTransport";
+import { MatrixRTCMode } from "../config/ConfigOptions";

 /**
 * Configuration and access tokens provided by the SFU on successful authentication.
@@ -80,11 +80,10 @@ export type OpenIDClientParts = Pick<
 * @param serviceUrl The URL of the livekit SFU service
 * @param roomId The room id used in the jwt request. This is NOT the livekit_alias. The jwt service will provide the alias. It maps matrix room ids <-> Livekit aliases.
 * @param opts Additional options to modify which endpoint with which data will be used to acquire the jwt token.
- * @param opts.forceJwtEndpoint This will use the old jwt endpoint which will create the rtc backend identity based on string concatenation
- * instead of a hash.
+ * @param opts.matrixRTCMode Determines which version of the JWT endpoint to use, which affects whether the
+ * RTC backend identity is based on string concatenation (legacy) or a hash (Matrix 2.0).
 * This function by default uses whatever is possible with the current jwt service installed next to the SFU.
 * For remote connections this does not matter, since we will not publish there we can rely on the newest option.
- * For our own connection we can only use the hashed version if we also send the new matrix2.0 sticky events.
 * @param opts.delayEndpointBaseUrl The URL of the matrix homeserver.
 * @param opts.delayId The delay id used for the jwt service to manage.
 * @param logger optional logger.
@@ -97,7 +96,7 @@ export async function getSFUConfigWithOpenID(
  serviceUrl: string,
  roomId: string,
  opts?: {
-    forceJwtEndpoint?: JwtEndpointVersion;
+    matrixRTCMode?: MatrixRTCMode;
    delayEndpointBaseUrl?: string;
    delayId?: string;
  },
@@ -116,19 +115,18 @@ export async function getSFUConfigWithOpenID(
  logger?.debug("Got openID token", openIdToken);
  let sfuConfig: { url: string; jwt: string } | undefined;

-  const tryBothJwtEndpoints = opts?.forceJwtEndpoint === undefined; // This is for SFUs where we do not publish.
+  const tryBothJwtEndpoints = opts?.matrixRTCMode === undefined; // This is for SFUs where we do not publish.

-  const forceMatrix2Jwt =
-    opts?.forceJwtEndpoint === JwtEndpointVersion.Matrix_2_0;
+  const forceMatrix2Jwt = opts?.matrixRTCMode === MatrixRTCMode.Matrix_2_0;

  // We want to start using the new endpoint (with optional delay delegation)
  // if we can use both or if we are forced to use the new one.
  if (tryBothJwtEndpoints || forceMatrix2Jwt) {
    try {
      logger?.info(
-        `Trying to get JWT with delegation for focus ${serviceUrl}...`,
+        `Trying to get JWT via default endpoint for focus ${serviceUrl}...`,
      );
-      const sfuConfig = await getLiveKitJWTWithDelayDelegation(
+      const sfuConfig = await getLiveKitJWT(
        membership,
        serviceUrl,
        roomId,
@@ -154,7 +152,7 @@ export async function getSFUConfigWithOpenID(
    logger?.info(
      `Trying to get JWT with legacy endpoint for focus ${serviceUrl}...`,
    );
-    sfuConfig = await getLiveKitJWT(
+    sfuConfig = await getLiveKitJWTLegacy(
      membership.deviceId,
      serviceUrl,
      roomId,
@@ -188,7 +186,7 @@ function extractFullConfigFromToken(sfuConfig: {
  };
 }

-async function getLiveKitJWT(
+async function getLiveKitJWTLegacy(
  deviceId: string,
  livekitServiceURL: string,
  matrixRoomId: string,
@@ -204,11 +202,10 @@ async function getLiveKitJWT(
  let bodyDalayParts: IDelayParams = {};
  // Also check for empty string
  if (delayId && delayEndpointBaseUrl) {
-    const delayTimeoutMs =
-      Config.get().matrix_rtc_session?.delayed_leave_event_delay_ms;
    bodyDalayParts = {
      delay_id: delayId,
-      delay_timeout: delayTimeoutMs,
+      delay_timeout:
+        Config.get().matrix_rtc_session.delegated_delayed_leave.delay_ms,
      delay_cs_api_url: delayEndpointBaseUrl,
    };
  }
@@ -264,7 +261,7 @@ class NotSupportedError extends Error {
  }
 }

-export async function getLiveKitJWTWithDelayDelegation(
+export async function getLiveKitJWT(
  membership: CallMembershipIdentityParts,
  livekitServiceURL: string,
  matrixRoomId: string,
@@ -288,11 +285,10 @@ export async function getLiveKitJWTWithDelayDelegation(
  let bodyDalayParts = {};
  // Also check for empty string
  if (delayId && delayEndpointBaseUrl) {
-    const delayTimeoutMs =
-      Config.get().matrix_rtc_session?.delayed_leave_event_delay_ms;
    bodyDalayParts = {
      delay_id: delayId,
-      delay_timeout: delayTimeoutMs,
+      delay_timeout:
+        Config.get().matrix_rtc_session.delegated_delayed_leave.delay_ms,
      delay_cs_api_url: delayEndpointBaseUrl,
    };
  }
@@ -135,7 +135,9 @@ export const ActiveCall: FC<ActiveCallProps> = (props) => {
        encryptionSystem: props.e2eeSystem,
        autoLeaveWhenOthersLeft,
        waitForCallPickup: waitForCallPickup && sendNotificationType === "ring",
-        matrixRTCMode$: matrixRTCModeSetting.value$,
+        // We merely sample the current mode here, so the user would need to
+        // manually rejoin to switch to a different one.
+        matrixRTCMode: matrixRTCModeSetting.value$.value,
      },
      reactionsReader.raisedHands$,
      reactionsReader.reactions$,
@@ -54,7 +54,6 @@ import { type IMembershipManager } from "matrix-js-sdk/lib/matrixrtc/IMembership
 import {
  createToggle$,
  filterBehavior,
-  generateItem,
  generateItems,
  pauseWhen,
 } from "../../utils/observable";
@@ -64,7 +63,10 @@ import {
  showReactions,
 } from "../../settings/settings";
 import { Config } from "../../config/Config";
-import { MatrixRTCMode } from "../../config/ConfigOptions";
+import {
+  MatrixRTCMode,
+  type ResolvedDelayedLeaveTimings,
+} from "../../config/ConfigOptions";
 import { isFirefox, platform } from "../../Platform";
 import { setPipEnabled$ } from "../../controls";
 import { TileStore } from "../TileStore";
@@ -110,7 +112,6 @@ import {
 } from "./localMember/LocalMember.ts";
 import {
  createLocalTransport$,
-  JwtEndpointVersion,
  type LocalTransport,
 } from "./localMember/LocalTransport.ts";
 import {
@@ -188,7 +189,7 @@ export interface CallViewModelOptions {
  /** Optional value overriding the connection factory, for testing purposes. */
  connectionFactory?: ConnectionFactory;
  /** The version & compatibility mode of MatrixRTC that we should use. */
-  matrixRTCMode$?: Behavior<MatrixRTCMode>;
+  matrixRTCMode?: MatrixRTCMode;
  /** Optional behavior overriding for the screensharing, for testing */
  toggleScreensharing?: () => void;
 }
@@ -450,10 +451,8 @@ export function createCallViewModel$(
  const configMatrixRTCMode = Config.get().matrix_rtc_mode as
    | MatrixRTCMode
    | undefined;
-  const matrixRTCMode$ =
-    configMatrixRTCMode !== undefined
-      ? constant(configMatrixRTCMode)
-      : (options.matrixRTCMode$ ?? constant(MatrixRTCMode.Compatibility));
+  const matrixRTCMode =
+    configMatrixRTCMode ?? options.matrixRTCMode ?? MatrixRTCMode.Compatibility;

  // Each hbar seperates a block of input variables required for the CallViewModel to function.
  // The outputs of this block is written under the hbar.
@@ -487,38 +486,16 @@ export function createCallViewModel$(
    memberId: uuidv4(),
  };

-  const localTransport$ = scope.behavior(
-    matrixRTCMode$.pipe(
-      generateItem(
-        "CallViewModel localTransport$",
-        // Re-create LocalTransport whenever the mode changes
-        (mode) => ({ keys: [mode], data: undefined }),
-        (scope, _data$, mode) =>
-          options.localTransport ??
-          createLocalTransport$({
-            scope: scope,
-            memberships$: memberships$,
-            ownMembershipIdentity,
-            client,
-            delayId$: scope.behavior(
-              (
-                fromEvent(
-                  matrixRTCSession,
-                  MembershipManagerEvent.DelayIdChanged,
-                  // The type of reemitted event includes the original emitted as the second arg.
-                ) as Observable<[string | undefined, IMembershipManager]>
-              ).pipe(map(([delayId]) => delayId ?? null)),
-              matrixRTCSession.delayId ?? null,
-            ),
-            roomId: matrixRoom.roomId,
-            forceJwtEndpoint:
-              mode === MatrixRTCMode.Matrix_2_0
-                ? JwtEndpointVersion.Matrix_2_0
-                : JwtEndpointVersion.Legacy,
-          }),
-      ),
-    ),
-  );
+  const localTransport =
+    options.localTransport ??
+    createLocalTransport$({
+      scope: scope,
+      memberships$: memberships$,
+      ownMembershipIdentity,
+      client,
+      roomId: matrixRoom.roomId,
+      matrixRTCMode,
+    });

  const connectionFactory =
    options.connectionFactory ??
@@ -536,8 +513,7 @@ export function createCallViewModel$(
    scope: scope,
    connectionFactory: connectionFactory,
    localTransport$: scope.behavior(
-      localTransport$.pipe(
-        switchMap((t) => t.active$),
+      localTransport.active$.pipe(
        catchError((e: unknown) => {
          logger.info(
            "could not pass local transport to createConnectionManager$. localTransport$ threw an error",
@@ -562,16 +538,6 @@ export function createCallViewModel$(
    localUser: { userId, deviceId },
  });

-  const connectOptions$ = scope.behavior(
-    matrixRTCMode$.pipe(
-      map((mode) => ({
-        encryptMedia: livekitKeyProvider !== undefined,
-        // TODO. This might need to get called again on each change of matrixRTCMode...
-        matrixRTCMode: mode,
-      })),
-    ),
-  );
-
  const localMembership = createLocalMembership$({
    scope,
    homeserverConnected: createHomeserverConnected$(
@@ -580,12 +546,19 @@ export function createCallViewModel$(
      matrixRTCSession,
    ),
    muteStates,
-    joinMatrixRTC: (transport: LivekitTransportConfig) => {
+    joinMatrixRTC: (
+      transport: LivekitTransportConfig,
+      delayedLeaveTimings: ResolvedDelayedLeaveTimings,
+    ) => {
      return enterRTCSession(
        matrixRTCSession,
        ownMembershipIdentity,
        transport,
-        connectOptions$.value,
+        {
+          encryptMedia: livekitKeyProvider !== undefined,
+          matrixRTCMode,
+          delayedLeaveTimings,
+        },
      );
    },
    createPublisherFactory: (connection: Connection) => {
@@ -600,9 +573,23 @@ export function createCallViewModel$(
      );
    },
    connectionManager,
+    client,
    matrixRTCSession,
-    localTransport$,
+    localTransport,
    roomId: matrixRoom.roomId,
+    baseUrl: client.baseUrl,
+    ownMembershipIdentity,
+    delayId$: scope.behavior(
+      (
+        fromEvent(
+          matrixRTCSession,
+          MembershipManagerEvent.DelayIdChanged,
+          // The type of reemitted event includes the original emitted as the second arg.
+        ) as Observable<[string | undefined, IMembershipManager]>
+      ).pipe(map(([delayId]) => delayId ?? null)),
+      matrixRTCSession.delayId ?? null,
+    ),
+    matrixRTCMode,
    logger: logger.getChild(`[${Date.now()}]`),
  });

@@ -238,7 +238,7 @@ export function withCallViewModel(mode: MatrixRTCMode) {
            );
          },
        },
-        matrixRTCMode$: constant(mode),
+        matrixRTCMode: mode,
        ...options,
      },
      raisedHands$,
@@ -19,13 +19,18 @@ import {
  beforeAll,
  afterAll,
  beforeEach,
+  afterEach,
 } from "vitest";
 import { BehaviorSubject, map, of } from "rxjs";
 import { logger } from "matrix-js-sdk/lib/logger";
 import { type LocalParticipant, type LocalTrack } from "livekit-client";
+import fetchMock from "fetch-mock";

 import { PosthogAnalytics } from "../../../analytics/PosthogAnalytics";
-import { MatrixRTCMode } from "../../../config/ConfigOptions";
+import {
+  MatrixRTCMode,
+  type ResolvedDelayedLeaveTimings,
+} from "../../../config/ConfigOptions";
 import { type HomeserverDisconnectReason } from "./HomeserverConnected";
 import {
  flushPromises,
@@ -35,6 +40,7 @@ import {
  mockMuteStates,
  withTestScheduler,
  ownMemberMock,
+  testScope,
 } from "../../../utils/test";
 import {
  TransportState,
@@ -58,6 +64,7 @@ import {
  type LocalTransport,
  type LocalTransportWithSFUConfig,
 } from "./LocalTransport";
+import * as openIDSFU from "../../../livekit/openIDSFU";

 initializeWidget();

@@ -95,112 +102,112 @@ describe("watchScreenShareToggle", () => {
  });
 });

-describe("LocalMembership", () => {
-  describe("enterRTCSession", () => {
-    it("It joins the correct Session", () => {
-      mockConfig({
-        livekit: { livekit_service_url: "http://my-default-service-url.com" },
-      });
+const timings: ResolvedDelayedLeaveTimings = {
+  delay_ms: 10000,
+  restart_ms: 4000,
+  restart_timeout_ms: 1000,
+};

-      const mockedSession = vi.mocked({
-        room: {
-          roomId: "roomId",
-          client: {
-            getDomain: vi.fn().mockReturnValue("example.org"),
-            getOpenIdToken: vi.fn().mockResolvedValue({
-              access_token: "ACCCESS_TOKEN",
-              token_type: "Bearer",
-              matrix_server_name: "localhost",
-              expires_in: 10000,
-            }),
-          },
-        },
-        memberships: [],
-        joinRTCSession: vi.fn(),
-      }) as unknown as MatrixRTCSession;
+const delegatedTimings: ResolvedDelayedLeaveTimings = {
+  delay_ms: timings.delay_ms * 10,
+  restart_ms: timings.restart_ms! * 10,
+  restart_timeout_ms: timings.restart_timeout_ms! * 10,
+};

-      enterRTCSession(
-        mockedSession,
-        ownMemberMock,
-        {
-          livekit_alias: "roomId",
-          livekit_service_url: "http://my-livekit-service-url.com",
-          type: "livekit",
-        },
-        {
-          encryptMedia: true,
-          matrixRTCMode: MATRIX_RTC_MODE,
-        },
-      );
+const mockedClient = {
+  getDomain: vi.fn().mockReturnValue("example.org"),
+  getDeviceId: vi.fn().mockReturnValue("AAAA"),
+  getOpenIdToken: vi.fn().mockResolvedValue({
+    access_token: "ACCCESS_TOKEN",
+    token_type: "Bearer",
+    matrix_server_name: "localhost",
+    expires_in: 10000,
+  }),
+};

-      expect(mockedSession.joinRTCSession).toHaveBeenLastCalledWith(
-        {
-          deviceId: "DEVICE",
-          memberId: "@alice:example.org:DEVICE",
-          userId: "@alice:example.org",
-        },
-        [],
-        {
-          livekit_alias: "roomId",
-          livekit_service_url: "http://my-livekit-service-url.com",
-          type: "livekit",
-        },
-        expect.objectContaining({ manageMediaKeys: true }),
-      );
-    });
+describe("enterRTCSession", () => {
+  const transport: LivekitTransportConfig = {
+    livekit_alias: "roomId",
+    livekit_service_url: "http://my-livekit-service-url.com",
+    type: "livekit",
+  };

-    it("passes keyRotationParticipantLimit from config to joinRTCSession", () => {
-      mockConfig({
-        livekit: { livekit_service_url: "http://my-default-service-url.com" },
-        matrix_rtc_session: {
-          delayed_leave_event_delay_ms: 0,
-          network_error_retry_ms: 0,
-          key_rotation_participant_limit: 50,
-        },
-      });
+  const options = {
+    encryptMedia: true,
+    matrixRTCMode: MATRIX_RTC_MODE,
+    delayedLeaveTimings: timings,
+  };

-      const mockedSession = vi.mocked({
-        room: {
-          roomId: "roomId",
-          client: {
-            getDomain: vi.fn().mockReturnValue("example.org"),
-            getOpenIdToken: vi.fn().mockResolvedValue({
-              access_token: "ACCCESS_TOKEN",
-              token_type: "Bearer",
-              matrix_server_name: "localhost",
-              expires_in: 10000,
-            }),
-          },
-        },
-        memberships: [],
-        joinRTCSession: vi.fn(),
-      }) as unknown as MatrixRTCSession;
+  const mockedSession = vi.mocked({
+    room: {
+      roomId: "roomId",
+      client: mockedClient,
+    },
+    memberships: [],
+    joinRTCSession: vi.fn(),
+  }) as unknown as MatrixRTCSession;

-      enterRTCSession(
-        mockedSession,
-        ownMemberMock,
-        {
-          livekit_alias: "roomId",
-          livekit_service_url: "http://my-livekit-service-url.com",
-          type: "livekit",
-        },
-        {
-          encryptMedia: true,
-          matrixRTCMode: MATRIX_RTC_MODE,
-        },
-      );
+  beforeEach(() =>
+    mockConfig({
+      livekit: { livekit_service_url: "http://my-default-service-url.com" },
+    }),
+  );

-      expect(mockedSession.joinRTCSession).toHaveBeenLastCalledWith(
-        expect.any(Object),
-        [],
-        expect.any(Object),
-        expect.objectContaining({
-          keyRotationParticipantLimit: 50,
-        }),
-      );
-    });
+  it("It joins the correct Session", () => {
+    enterRTCSession(mockedSession, ownMemberMock, transport, options);
+
+    expect(mockedSession.joinRTCSession).toHaveBeenLastCalledWith(
+      {
+        deviceId: "DEVICE",
+        memberId: "@alice:example.org:DEVICE",
+        userId: "@alice:example.org",
+      },
+      [],
+      transport,
+      expect.objectContaining({ manageMediaKeys: true }),
+    );
  });

+  it("passes keyRotationParticipantLimit from config to joinRTCSession", () => {
+    mockConfig({
+      livekit: { livekit_service_url: "http://my-default-service-url.com" },
+      matrix_rtc_session: {
+        network_error_retry_ms: 0,
+        key_rotation_participant_limit: 50,
+        delayed_leave: timings,
+        delegated_delayed_leave: timings,
+      },
+    });
+
+    enterRTCSession(mockedSession, ownMemberMock, transport, options);
+
+    expect(mockedSession.joinRTCSession).toHaveBeenLastCalledWith(
+      expect.any(Object),
+      [],
+      expect.any(Object),
+      expect.objectContaining({
+        keyRotationParticipantLimit: 50,
+      }),
+    );
+  });
+
+  it("uses the specified delayed leave timings", () => {
+    enterRTCSession(mockedSession, ownMemberMock, transport, options);
+
+    expect(mockedSession.joinRTCSession).toHaveBeenLastCalledWith(
+      expect.anything(),
+      expect.anything(),
+      expect.anything(),
+      expect.objectContaining({
+        delayedLeaveEventRestartMs: timings.restart_ms,
+        delayedLeaveEventDelayMs: timings.delay_ms,
+        delayedLeaveEventRestartLocalTimeoutMs: timings.restart_timeout_ms,
+      }),
+    );
+  });
+});
+
+describe("LocalMembership", () => {
  const defaultCreateLocalMemberValues = {
    options: constant({
      encryptMedia: false,
@@ -226,8 +233,30 @@ describe("LocalMembership", () => {
      rtsSession$: constant(RTCMemberStatus.Connected),
    },
    roomId: "!test-room-id:example.org",
+    baseUrl: "https://matrix.example.org",
+    ownMembershipIdentity: ownMemberMock,
+    client: mockedClient,
+    delayId$: constant(null),
+    matrixRTCMode: MATRIX_RTC_MODE,
  };

+  beforeEach(() => {
+    mockConfig({
+      livekit: { livekit_service_url: "http://my-default-service-url.com" },
+      matrix_rtc_session: {
+        network_error_retry_ms: 1000,
+        delayed_leave: timings,
+        delegated_delayed_leave: delegatedTimings,
+      },
+    });
+    fetchMock.catch(404);
+  });
+
+  afterEach(async () => {
+    void (await fetchMock.flush());
+    fetchMock.reset();
+  });
+
  it("throws error on missing RTC config error", () => {
    withTestScheduler(({ scope, hot, behavior, expectObservable }) => {
      const localTransport$ = scope.behavior<null | LivekitTransportConfig>(
@@ -254,9 +283,8 @@ describe("LocalMembership", () => {
        scope,
        ...defaultCreateLocalMemberValues,
        connectionManager: mockConnectionManager,
-        localTransport$: behavior("a", { a: aLocalTransport }),
+        localTransport: aLocalTransport,
      });
-      localMembership.requestJoinAndPublish();

      expectObservable(localMembership.localMemberState$).toBe("ne", {
        n: TransportState.Waiting,
@@ -299,9 +327,8 @@ describe("LocalMembership", () => {
        scope,
        ...defaultCreateLocalMemberValues,
        connectionManager: mockConnectionManager,
-        localTransport$: behavior("a", { a: aLocalTransport }),
+        localTransport: aLocalTransport,
      });
-      localMembership.requestJoinAndPublish();

      expectObservable(localMembership.localMemberState$).toBe("n-e", {
        n: TransportState.Waiting,
@@ -317,8 +344,8 @@ describe("LocalMembership", () => {
    const scope = new ObservableScope();

    const aLocalTransport: LocalTransport = {
-      advertised$: new BehaviorSubject(aTransport),
-      active$: new BehaviorSubject(aTransportWithSFUConfig),
+      advertised$: constant(aTransport),
+      active$: constant(aTransportWithSFUConfig),
    };

    const mockConnectionManager = {
@@ -336,7 +363,7 @@ describe("LocalMembership", () => {
        leaveRoomSession: vi.fn(),
      },
      connectionManager: mockConnectionManager,
-      localTransport$: new BehaviorSubject(aLocalTransport),
+      localTransport: aLocalTransport,
    });
    const expextedLog =
      "'not connected yet' while updating the call intent (this is expected on startup)";
@@ -397,12 +424,90 @@ describe("LocalMembership", () => {
    livekitRoom: mockLivekitRoom({}),
  } as unknown as Connection;

+  const authCallSpy = vi
+    .spyOn(openIDSFU, "getSFUConfigWithOpenID")
+    .mockImplementation(() => mockedClient.getOpenIdToken());
+  afterEach(() => authCallSpy.mockClear());
+
+  it.each([
+    ["no", null, timings],
+    [
+      "homeserver",
+      "https://matrix.example.org/_matrix/client/unstable/io.element.msc4195/rtc/livekit/delegate_delayed_leave",
+      delegatedTimings,
+    ],
+    ["transport", "/a/delegate_delayed_leave", delegatedTimings],
+  ])(
+    "joins session with %s delegation support",
+    async (_serviceName, delegationUrl, delayedLeaveTimings) => {
+      const scope = testScope();
+      const joinMatrixRTC = vi.fn();
+      const delayId$ = new BehaviorSubject<string | null>(null);
+
+      if (delegationUrl !== null)
+        fetchMock.post(delegationUrl, () => ({ status: 401, body: {} }));
+
+      const localMembership = createLocalMembership$({
+        scope,
+        ...defaultCreateLocalMemberValues,
+        connectionManager: {
+          connectionManagerData$: constant(
+            new Epoch(new ConnectionManagerData()),
+          ),
+        },
+        joinMatrixRTC,
+        localTransport: {
+          advertised$: constant(aTransport),
+          active$: constant(aTransportWithSFUConfig),
+        },
+        delayId$,
+      });
+
+      localMembership.requestJoinAndPublish();
+      void (await fetchMock.flush());
+      await flushPromises();
+      // Joins with timings appropriate for the level of delegation support
+      expect(joinMatrixRTC).toHaveBeenCalledWith(
+        aTransport,
+        delayedLeaveTimings,
+      );
+
+      expect(authCallSpy).not.toHaveBeenCalled();
+      delayId$.next("leave1");
+      await flushPromises();
+      if (delegationUrl === null) {
+        expect(authCallSpy).not.toHaveBeenCalled();
+      } else {
+        // Delegation is supported in this test case, so go on to check that
+        // LocalMember actually performs delegation
+        const expectDelegation = (delayId: string) =>
+          expect(authCallSpy).toHaveBeenLastCalledWith(
+            mockedClient,
+            ownMemberMock,
+            "a",
+            "!test-room-id:example.org",
+            {
+              matrixRTCMode: MATRIX_RTC_MODE,
+              delayEndpointBaseUrl: "https://matrix.example.org",
+              delayId,
+            },
+            expect.anything(),
+          );
+
+        expectDelegation("leave1");
+        delayId$.next("leave2"); // Can change delegated leaves
+        await flushPromises();
+        expectDelegation("leave2");
+      }
+    },
+  );
+
  it("recreates publisher if new connection is used, always unpublish and end tracks", async () => {
    const scope = new ObservableScope();

    const activeTransport$ = new BehaviorSubject(aTransportWithSFUConfig);
    const aLocalTransport: LocalTransport = {
-      advertised$: new BehaviorSubject(aTransport),
+      advertised$: constant(aTransport),
      active$: activeTransport$,
    };

@@ -440,7 +545,7 @@ describe("LocalMembership", () => {
      connectionManager: {
        connectionManagerData$: constant(new Epoch(connectionManagerData)),
      },
-      localTransport$: new BehaviorSubject(aLocalTransport),
+      localTransport: aLocalTransport,
    });
    await flushPromises();
    activeTransport$.next({
@@ -471,7 +576,7 @@ describe("LocalMembership", () => {
    const publishers: Publisher[] = [];

    const tracks$ = new BehaviorSubject<LocalTrack[]>([]);
-    const publishing$ = new BehaviorSubject<boolean>(false);
+    const publishing$ = constant<boolean>(false);
    defaultCreateLocalMemberValues.createPublisherFactory.mockImplementation(
      () => {
        const p = {
@@ -495,8 +600,8 @@ describe("LocalMembership", () => {
      >;

    const aLocalTransport: LocalTransport = {
-      advertised$: new BehaviorSubject(aTransport),
-      active$: new BehaviorSubject(aTransportWithSFUConfig),
+      advertised$: constant(aTransport),
+      active$: constant(aTransportWithSFUConfig),
    };

    const connectionManagerData = new ConnectionManagerData();
@@ -508,7 +613,7 @@ describe("LocalMembership", () => {
      connectionManager: {
        connectionManagerData$: constant(new Epoch(connectionManagerData)),
      },
-      localTransport$: new BehaviorSubject(aLocalTransport),
+      localTransport: aLocalTransport,
    });
    await flushPromises();
    expect(publisherFactory).toHaveBeenCalledOnce();
@@ -536,7 +641,7 @@ describe("LocalMembership", () => {
      new BehaviorSubject<null | LocalTransportWithSFUConfig>(null);

    const aLocalTransport: LocalTransport = {
-      advertised$: new BehaviorSubject(aTransport),
+      advertised$: constant(aTransport),
      active$: activeTransport$,
    };

@@ -579,7 +684,7 @@ describe("LocalMembership", () => {
      connectionManager: {
        connectionManagerData$,
      },
-      localTransport$: new BehaviorSubject(aLocalTransport),
+      localTransport: aLocalTransport,
    });

    await flushPromises();
@@ -714,10 +819,10 @@ describe("LocalMembership", () => {
        connectionManager: {
          connectionManagerData$: constant(new Epoch(connectionManagerData)),
        },
-        localTransport$: new BehaviorSubject({
-          advertised$: new BehaviorSubject(aTransport),
-          active$: new BehaviorSubject(aTransportWithSFUConfig),
-        }),
+        localTransport: {
+          advertised$: constant(aTransport),
+          active$: constant(aTransportWithSFUConfig),
+        },
      });

      await flushPromises();
@@ -754,10 +859,10 @@ describe("LocalMembership", () => {
        connectionManager: {
          connectionManagerData$: constant(new Epoch(connectionManagerData)),
        },
-        localTransport$: new BehaviorSubject({
-          advertised$: new BehaviorSubject(aTransport),
-          active$: new BehaviorSubject(aTransportWithSFUConfig),
-        }),
+        localTransport: {
+          advertised$: constant(aTransport),
+          active$: constant(aTransportWithSFUConfig),
+        },
      });

      await flushPromises();
@@ -796,18 +901,19 @@ describe("LocalMembership", () => {
        scope,
        ...defaultCreateLocalMemberValues,
        homeserverConnected: {
-          combined$: new BehaviorSubject<
-            [boolean, HomeserverDisconnectReason | null]
-          >([true, null]),
+          combined$: constant<[boolean, HomeserverDisconnectReason | null]>([
+            true,
+            null,
+          ]),
          rtsSession$: constant(RTCMemberStatus.Connected),
        },
        connectionManager: {
          connectionManagerData$: constant(new Epoch(connectionManagerData)),
        },
-        localTransport$: new BehaviorSubject({
-          advertised$: new BehaviorSubject(aTransport),
-          active$: new BehaviorSubject(aTransportWithSFUConfig),
-        }),
+        localTransport: {
+          advertised$: constant(aTransport),
+          active$: constant(aTransportWithSFUConfig),
+        },
      });

      await flushPromises();
@@ -848,10 +954,10 @@ describe("LocalMembership", () => {
        connectionManager: {
          connectionManagerData$: constant(new Epoch(connectionManagerData)),
        },
-        localTransport$: new BehaviorSubject({
-          advertised$: new BehaviorSubject(aTransport),
-          active$: new BehaviorSubject(aTransportWithSFUConfig),
-        }),
+        localTransport: {
+          advertised$: constant(aTransport),
+          active$: constant(aTransportWithSFUConfig),
+        },
      });

      await flushPromises();
@@ -917,10 +1023,10 @@ describe("LocalMembership", () => {
        connectionManager: {
          connectionManagerData$: constant(new Epoch(connectionManagerData)),
        },
-        localTransport$: new BehaviorSubject({
-          advertised$: new BehaviorSubject(aTransport),
-          active$: new BehaviorSubject(aTransportWithSFUConfig),
-        }),
+        localTransport: {
+          advertised$: constant(aTransport),
+          active$: constant(aTransportWithSFUConfig),
+        },
      });
      return { scope, localMembership };
    };
@@ -15,6 +15,7 @@ import {
  MediaDeviceFailure,
 } from "livekit-client";
 import { observeParticipantEvents } from "@livekit/components-core";
+import { type MatrixClient } from "matrix-js-sdk";
 import {
  Status as RTCSessionStatus,
  type LivekitTransport,
@@ -62,7 +63,10 @@ import {
  screenShareCodec,
  parseResolution,
 } from "../../../settings/settings.ts";
-import { MatrixRTCMode } from "../../../config/ConfigOptions.ts";
+import {
+  MatrixRTCMode,
+  type ResolvedDelayedLeaveTimings,
+} from "../../../config/ConfigOptions.ts";
 import { Config } from "../../../config/Config.ts";
 import {
  ConnectionState,
@@ -72,6 +76,8 @@ import {
 import { type HomeserverConnected } from "./HomeserverConnected.ts";
 import { type LocalTransport } from "./LocalTransport.ts";
 import { areLivekitTransportsEqual } from "../remoteMembers/MatrixLivekitMembers.ts";
+import { or$ } from "../../../utils/observable.ts";
+import { getSFUConfigWithOpenID } from "../../../livekit/openIDSFU.ts";

 export enum TransportState {
  /** Not even a transport is available to the LocalMembership */
@@ -133,14 +139,22 @@ interface Props {
  muteStates: MuteStates;
  connectionManager: IConnectionManager;
  createPublisherFactory: (connection: Connection) => Publisher;
-  joinMatrixRTC: (transport: LivekitTransportConfig) => void;
+  joinMatrixRTC: (
+    transport: LivekitTransportConfig,
+    delayedLeaveTimings: ResolvedDelayedLeaveTimings,
+  ) => void;
  homeserverConnected: HomeserverConnected;
  roomId: string;
-  localTransport$: Behavior<LocalTransport>;
+  ownMembershipIdentity: CallMembershipIdentityParts;
+  localTransport: LocalTransport;
+  client: Pick<MatrixClient, "getDeviceId" | "getOpenIdToken">;
  matrixRTCSession: Pick<
    MatrixRTCSession,
    "updateCallIntent" | "leaveRoomSession"
  >;
+  baseUrl: string;
+  delayId$: Behavior<string | null>;
+  matrixRTCMode: MatrixRTCMode;
  logger: Logger;
 }

@@ -155,10 +169,12 @@ interface Props {
 * @param props.createPublisherFactory Factory to create a publisher once we have a connection.
 * @param props.joinMatrixRTC Callback to join the matrix RTC session once we have a transport.
 * @param props.homeserverConnected The homeserver connected state.
- * @param props.localTransport$ The transport to advertise in our membership.
+ * @param props.localTransport The transport to advertise in our membership.
 * @param props.logger The logger to use.
 * @param props.muteStates The mute states for video and audio.
 * @param props.matrixRTCSession The matrix RTC session to join.
+ * @param props.baseUrl Base URL of the homeserver.
+ * @param props.delayId$ ID of the delayed leave event to delegate to the SFU.
 * @param props.roomId The room ID used as the call identifier in analytics events.
 * @returns
 *  - publisher: The handle to create tracks and publish them to the room.
@@ -170,14 +186,19 @@ interface Props {
 export const createLocalMembership$ = ({
  scope,
  connectionManager,
-  localTransport$,
+  localTransport,
  homeserverConnected,
  createPublisherFactory,
  joinMatrixRTC,
  logger: parentLogger,
  muteStates,
+  client,
  matrixRTCSession,
+  baseUrl,
  roomId,
+  ownMembershipIdentity,
+  delayId$,
+  matrixRTCMode,
 }: Props): {
  /**
   * This request to start audio and video tracks.
@@ -236,25 +257,69 @@ export const createLocalMembership$ = ({
    return of(null);
  };

-  // This is the transport that we will advertise in our membership.
-  const advertisedTransport$ = localTransport$.pipe(
-    switchMap((lt) => lt.advertised$),
+  async function checkDelegationSupport(
+    endpointUrl: string,
+    serviceName: string,
+  ): Promise<boolean> {
+    logger.info(`Checking whether ${serviceName} supports delegation…`);
+    try {
+      // Bluntly hit the endpoint without auth to check for a 404. Unfortunately
+      // we can't wrap this in a retry loop, as many servers don't just disable
+      // delegation support, but in fact are from a time before the endpoint
+      // existed at all, therefore we can hit CORS errors which would just gum
+      // up the retry loop. (May be revisited after Matrix 2.0.)
+      const res = await fetch(endpointUrl, { method: "POST" });
+      if (res.status === 404) {
+        logger.warn(`${serviceName} does not support delegation`);
+        return false;
+      } else {
+        logger.info(`${serviceName} supports delegation`);
+        return true;
+      }
+    } catch (e) {
+      logger.warn(
+        `Failed to determine whether ${serviceName} supports delegation, assuming no support`,
+        e,
+      );
+      return false;
+    }
+  }
+
+  const homeserverSupportsDelegation = checkDelegationSupport(
+    baseUrl +
+      "/_matrix/client/unstable/io.element.msc4195/rtc/livekit/delegate_delayed_leave",
+    "homeserver",
+  );
+
+  // The transport that we will advertise in our membership, paired with info as
+  // to whether delayed event delegation is supported
+  const joinParams$ = localTransport.advertised$.pipe(
    catchError(handleTransportError),
    distinctUntilChanged(areLivekitTransportsEqual),
+    switchMap((transport) => {
+      if (transport === null) return of(null);
+      const transportSupportsDelegation = checkDelegationSupport(
+        transport.livekit_service_url + "/delegate_delayed_leave",
+        `transport ${transport.livekit_service_url}`,
+      );
+      return or$(
+        from(homeserverSupportsDelegation),
+        from(transportSupportsDelegation),
+      ).pipe(
+        map((delegationSupported) => ({ transport, delegationSupported })),
+        startWith(null),
+      );
+    }),
  );

  // Unwrap the local transport and set the state of the LocalMembership to error in case the transport is an error.
  const activeTransport$ = scope.behavior(
-    localTransport$.pipe(
-      switchMap((lt) => {
-        return combineLatest([lt.active$, lt.advertised$]).pipe(
-          map(([active, advertised]) => {
-            // Our policy is to not publish to another transport if our prefered transport is miss-configured
-            if (advertised == null) return null;
+    combineLatest([localTransport.active$, localTransport.advertised$]).pipe(
+      map(([active, advertised]) => {
+        // Our policy is to not publish to another transport if our prefered transport is miss-configured
+        if (advertised == null) return null;

-            return active?.transport ?? null;
-          }),
-        );
+        return active?.transport ?? null;
      }),
      catchError(handleTransportError),
      distinctUntilChanged(areLivekitTransportsEqual),
@@ -617,16 +682,20 @@ export const createLocalMembership$ = ({

  // Keep matrix rtc session in sync with advertisedTransport$, connectRequested$
  scope.reconcile(
-    scope.behavior(
-      combineLatest([advertisedTransport$, joinAndPublishRequested$]),
-    ),
-    async ([transport, shouldConnect]) => {
-      if (!transport) return;
+    scope.behavior(combineLatest([joinParams$, joinAndPublishRequested$])),
+    async ([joinParams, shouldConnect]) => {
+      if (!joinParams) return;
      // if shouldConnect=false we will do the disconnect as the cleanup from the previous reconcile iteration.
      if (!shouldConnect) return;
+      const sessionConfig = Config.get().matrix_rtc_session;

      try {
-        joinMatrixRTC(transport);
+        joinMatrixRTC(
+          joinParams.transport,
+          joinParams.delegationSupported
+            ? sessionConfig.delegated_delayed_leave
+            : sessionConfig.delayed_leave,
+        );
      } catch (error) {
        logger.error("Error entering RTC session", error);
        if (error instanceof Error)
@@ -653,6 +722,34 @@ export const createLocalMembership$ = ({
    ),
  );

+  // Delegate delayed leaves to the SFU
+  scope.reconcile(
+    scope.behavior(combineLatest([joinParams$, delayId$])),
+    async ([joinParams, delayId]) => {
+      if (joinParams?.delegationSupported && delayId !== null) {
+        try {
+          // This will technically cause the service to issue a new JWT token,
+          // but it's safe to discard. We're only interested in triggering
+          // delegation.
+          await getSFUConfigWithOpenID(
+            client,
+            ownMembershipIdentity,
+            joinParams.transport.livekit_service_url,
+            roomId,
+            { matrixRTCMode, delayEndpointBaseUrl: baseUrl, delayId },
+            logger,
+          );
+        } catch (e) {
+          // TODO: Surface this to the user as a service interruption?
+          logger.error(
+            `Failed to delegate leave to ${joinParams.transport.livekit_service_url}`,
+            e,
+          );
+        }
+      }
+    },
+  );
+
  // Pause upstream of all local media tracks when we're disconnected from
  // MatrixRTC, because it can be an unpleasant surprise for the app to say
  // 'reconnecting' and yet still be transmitting your media to others.
@@ -864,6 +961,7 @@ export function observeSharingScreen$(p: Participant): Observable<boolean> {
 interface EnterRTCSessionOptions {
  encryptMedia: boolean;
  matrixRTCMode: MatrixRTCMode;
+  delayedLeaveTimings: ResolvedDelayedLeaveTimings;
 }

 /**
@@ -876,6 +974,7 @@ interface EnterRTCSessionOptions {
 * @param rtcSession - The MatrixRTCSession to join.
 * @param ownMembershipIdentity - Options for entering the RTC session.
 * @param transport - The LivekitTransport to use for this session.
+ * @param delayedLeaveTimings - The preferred timings for delayed leave events.
 * @param options - `encryptMedia`: Whether to encrypt media `matrixRTCMode`: The Matrix RTC mode to use.
 * @throws If the widget could not send ElementWidgetActions.JoinCall action.
 */
@@ -884,9 +983,8 @@ export function enterRTCSession(
  rtcSession: MatrixRTCSession,
  ownMembershipIdentity: CallMembershipIdentityParts,
  transport: LivekitTransportConfig,
-  options: EnterRTCSessionOptions,
+  { encryptMedia, matrixRTCMode, delayedLeaveTimings }: EnterRTCSessionOptions,
 ): void {
-  const { encryptMedia, matrixRTCMode } = options;
  PosthogAnalytics.instance.eventCallEnded.cacheStartCall(new Date());
  PosthogAnalytics.instance.eventCallStarted.track(rtcSession.room.roomId);

@@ -894,7 +992,11 @@ export function enterRTCSession(
  // have started tracking by the time calls start getting created.
  // groupCallOTelMembership?.onJoinCall();

-  const { matrix_rtc_session: matrixRtcSessionConfig } = Config.get();
+  const {
+    sync_disconnect_grace_period_ms: gracePeriod,
+    matrix_rtc_session: sessionConfig,
+  } = Config.get();
+  const retryInterval = sessionConfig.network_error_retry_ms;
  const { sendNotificationType: notificationType, callIntent } = getUrlParams();
  const multiSFU =
    matrixRTCMode === MatrixRTCMode.Compatibility ||
@@ -912,16 +1014,11 @@ export function enterRTCSession(
    };
  }

-  // Calculates `maximumNetworkErrorRetryCount`. The connection is failed if EITHER:
-  // - The /sync loop is unresponsive for > `gracePeriod` ms, or
-  // - A delayed leave event is emitted (after `leaveDelay` ms period).
-  // Note: Use leaveDelay >> gracePeriod for delegated leave events.
-  const gracePeriod = Config.get().sync_disconnect_grace_period_ms;
-  const leaveDelay = matrixRtcSessionConfig?.delayed_leave_event_delay_ms;
-  const retryInterval = matrixRtcSessionConfig?.network_error_retry_ms;
-
+  // Set maximumNetworkErrorRetryCount such that we will consider the client
+  // disconnected as soon as either it fails to sync for longer than the grace
+  // period, or it is likely that a delayed leave event has been sent.
  // Math.min is used to account for the respective worst case: /sync not available or leave event emitted.
-  const maxWaitTime = Math.min(gracePeriod, leaveDelay);
+  const maxWaitTime = Math.min(gracePeriod, delayedLeaveTimings.delay_ms);
  const maximumNetworkErrorRetryCount =
    Math.ceil(maxWaitTime / retryInterval) + 1;

@@ -936,18 +1033,14 @@ export function enterRTCSession(
      notificationType,
      callIntent,
      manageMediaKeys: encryptMedia,
-      delayedLeaveEventRestartMs:
-        matrixRtcSessionConfig?.delayed_leave_event_restart_ms,
-      delayedLeaveEventDelayMs:
-        matrixRtcSessionConfig?.delayed_leave_event_delay_ms,
+      delayedLeaveEventRestartMs: delayedLeaveTimings.restart_ms,
+      delayedLeaveEventDelayMs: delayedLeaveTimings.delay_ms,
      delayedLeaveEventRestartLocalTimeoutMs:
-        matrixRtcSessionConfig?.delayed_leave_event_restart_local_timeout_ms,
-      networkErrorRetryMs: matrixRtcSessionConfig?.network_error_retry_ms,
-      makeKeyDelay: matrixRtcSessionConfig?.wait_for_key_rotation_ms,
-      membershipEventExpiryMs:
-        matrixRtcSessionConfig?.membership_event_expiry_ms,
-      keyRotationParticipantLimit:
-        matrixRtcSessionConfig?.key_rotation_participant_limit,
+        delayedLeaveTimings.restart_timeout_ms,
+      networkErrorRetryMs: sessionConfig.network_error_retry_ms,
+      makeKeyDelay: sessionConfig.wait_for_key_rotation_ms,
+      membershipEventExpiryMs: sessionConfig.membership_event_expiry_ms,
+      keyRotationParticipantLimit: sessionConfig.key_rotation_participant_limit,
      unstableSendStickyEvents: matrixRTCMode === MatrixRTCMode.Matrix_2_0,
      maximumNetworkErrorRetryCount: maximumNetworkErrorRetryCount,
    },
@@ -14,11 +14,8 @@ import {
  type MockedObject,
  vi,
 } from "vitest";
-import {
-  type CallMembership,
-  type LivekitTransportConfig,
-} from "matrix-js-sdk/lib/matrixrtc";
-import { BehaviorSubject, filter, lastValueFrom } from "rxjs";
+import { type CallMembership } from "matrix-js-sdk/lib/matrixrtc";
+import { lastValueFrom } from "rxjs";
 import fetchMock from "fetch-mock";

 import {
@@ -27,11 +24,7 @@ import {
  ownMemberMock,
  testScope,
 } from "../../../utils/test";
-import {
-  createLocalTransport$,
-  JwtEndpointVersion,
-  type LocalTransportWithSFUConfig,
-} from "./LocalTransport";
+import { createLocalTransport$ } from "./LocalTransport";
 import { constant } from "../../Behavior";
 import { Epoch, ObservableScope } from "../../ObservableScope";
 import {
@@ -41,6 +34,7 @@ import {
 import * as openIDSFU from "../../../livekit/openIDSFU";
 import { customLivekitUrl } from "../../../settings/settings";
 import { testJWTToken } from "../../../utils/test-fixtures";
+import { MatrixRTCMode } from "../../../config/ConfigOptions";

 describe("LocalTransport", () => {
  const openIdResponse: openIDSFU.SFUConfig = {
@@ -61,14 +55,12 @@ describe("LocalTransport", () => {
        // eslint-disable-next-line @typescript-eslint/naming-convention
        _unstable_getRTCTransports: async () => Promise.resolve([]),
        getDomain: () => "example.org",
-        baseUrl: "example.org",
        // These won't be called in this error path but satisfy the type
        getOpenIdToken: vi.fn(),
        getDeviceId: vi.fn(),
      },
      ownMembershipIdentity: ownMemberMock,
-      forceJwtEndpoint: JwtEndpointVersion.Legacy,
-      delayId$: constant("delay_id_mock"),
+      matrixRTCMode: MatrixRTCMode.Compatibility,
    });
    await flushPromises();

@@ -100,7 +92,6 @@ describe("LocalTransport", () => {
      roomId: "!example_room_id",
      memberships$: constant(new Epoch<CallMembership[]>([])),
      client: {
-        baseUrl: "https://example.org",
        getDomain: () => "example.org",
        // eslint-disable-next-line @typescript-eslint/naming-convention
        _unstable_getRTCTransports: async () => Promise.resolve([]),
@@ -108,8 +99,7 @@ describe("LocalTransport", () => {
        getDeviceId: vi.fn(),
      },
      ownMembershipIdentity: ownMemberMock,
-      forceJwtEndpoint: JwtEndpointVersion.Legacy,
-      delayId$: constant("delay_id_mock"),
+      matrixRTCMode: MatrixRTCMode.Compatibility,
    });
    active$.subscribe(
      (o) => observations.push(o),
@@ -147,11 +137,9 @@ describe("LocalTransport", () => {
        getDomain: () => "example.org",
        getOpenIdToken: vi.fn(),
        getDeviceId: vi.fn(),
-        baseUrl: "https://example.org",
      },
      ownMembershipIdentity: ownMemberMock,
-      forceJwtEndpoint: JwtEndpointVersion.Legacy,
-      delayId$: constant("delay_id_mock"),
+      matrixRTCMode: MatrixRTCMode.Compatibility,
    });

    openIdResolver.resolve?.({
@@ -194,11 +182,9 @@ describe("LocalTransport", () => {
        ownMembershipIdentity: ownMemberMock,
        scope: testScope(),
        roomId: "!example_room_id",
-        forceJwtEndpoint: JwtEndpointVersion.Legacy,
-        delayId$: constant(null),
+        matrixRTCMode: MatrixRTCMode.Compatibility,
        memberships$: constant(new Epoch<CallMembership[]>([])),
        client: {
-          baseUrl: "https://example.org",
          getDomain: vi.fn().mockReturnValue("example.org"),
          // eslint-disable-next-line @typescript-eslint/naming-convention
          _unstable_getRTCTransports: vi.fn().mockResolvedValue([]),
@@ -306,12 +292,10 @@ describe("LocalTransport", () => {
        scope: testScope(),
        ownMembershipIdentity: ownMemberMock,
        roomId: "!example_room_id",
-        forceJwtEndpoint: JwtEndpointVersion.Legacy,
-        delayId$: constant(null),
+        matrixRTCMode: MatrixRTCMode.Compatibility,
        memberships$: constant(new Epoch<CallMembership[]>([])),
        client: {
          getDomain: () => "example.org",
-          baseUrl: "https://example.org",
          // eslint-disable-next-line @typescript-eslint/naming-convention
          _unstable_getRTCTransports: async () => Promise.resolve([]),
          // These won't be called in this error path but satisfy the type
@@ -329,84 +313,4 @@ describe("LocalTransport", () => {
      );
    });
  });
-
-  it("should not update advertised/active transport on delayID changes, but delay Id delegation should be called", async () => {
-    // For simplicity, we'll just use the config livekit
-    customLivekitUrl.setValue("https://lk.example.org");
-
-    const authCallSpy = vi
-      .spyOn(openIDSFU, "getSFUConfigWithOpenID")
-      .mockResolvedValue(openIdResponse);
-
-    const delayId$ = new BehaviorSubject<string | null>(null);
-
-    const { advertised$, active$ } = createLocalTransport$({
-      scope: testScope(),
-      ownMembershipIdentity: ownMemberMock,
-      roomId: "!example_room_id",
-      // We want multi-sdu
-      forceJwtEndpoint: JwtEndpointVersion.Legacy,
-      delayId$: delayId$,
-      memberships$: constant(new Epoch<CallMembership[]>([])),
-      client: {
-        getDomain: () => "example.org",
-        baseUrl: "https://example.org",
-        // eslint-disable-next-line @typescript-eslint/naming-convention
-        _unstable_getRTCTransports: async () => Promise.resolve([]),
-        // These won't be called in this error path but satisfy the type
-        getOpenIdToken: vi.fn(),
-        getDeviceId: vi.fn(),
-      },
-    });
-
-    const advertisedValues: LivekitTransportConfig[] = [];
-    const activeValues: LocalTransportWithSFUConfig[] = [];
-    advertised$
-      .pipe(filter((v) => v !== null))
-      .subscribe((t) => advertisedValues.push(t));
-    active$
-      .pipe(filter((v) => v !== null))
-      .subscribe((t) => activeValues.push(t));
-
-    await flushPromises();
-
-    // we have now an active and an advertised
-    expect(advertisedValues.length).toEqual(1);
-    expect(activeValues.length).toEqual(1);
-    expect(advertisedValues[0]!.livekit_service_url).toEqual(
-      "https://lk.example.org",
-    );
-    expect(activeValues[0]!.transport.livekit_service_url).toEqual(
-      "https://lk.example.org",
-    );
-
-    expect(authCallSpy).toHaveBeenCalledTimes(2);
-    // Now emits 3 new delays id
-    delayId$.next("delay_id_1");
-    await flushPromises();
-    delayId$.next("delay_id_2");
-    await flushPromises();
-    delayId$.next("delay_id_3");
-    await flushPromises();
-
-    // No new emissions should've happened, it is the same transport.
-    expect(advertisedValues.length).toEqual(1);
-    expect(activeValues.length).toEqual(1);
-
-    // Still we should have updated the delayID to auth
-    expect(authCallSpy).toHaveBeenCalledTimes(
-      4 * 2 /* 2 calls for each delayId ?? why */,
-    );
-
-    expect(authCallSpy).toHaveBeenLastCalledWith(
-      expect.anything(),
-      expect.anything(),
-      expect.anything(),
-      expect.anything(),
-      expect.objectContaining({
-        delayId: "delay_id_3",
-      }),
-      expect.anything(),
-    );
-  });
 });
@@ -10,14 +10,7 @@ import {
  type LivekitTransportConfig,
 } from "matrix-js-sdk/lib/matrixrtc";
 import { type MatrixClient } from "matrix-js-sdk";
-import {
-  combineLatest,
-  distinctUntilChanged,
-  from,
-  map,
-  of,
-  switchMap,
-} from "rxjs";
+import { distinctUntilChanged, from, map, of, switchMap } from "rxjs";
 import { logger as rootLogger, type Logger } from "matrix-js-sdk/lib/logger";
 import { type CallMembershipIdentityParts } from "matrix-js-sdk/lib/matrixrtc/EncryptionManager";

@@ -37,6 +30,7 @@ import {
 import { areLivekitTransportsEqual } from "../remoteMembers/MatrixLivekitMembers.ts";
 import { customLivekitUrl } from "../../../settings/settings.ts";
 import { RtcTransportAutoDiscovery } from "./RtcTransportAutoDiscovery.ts";
+import { type MatrixRTCMode } from "../../../config/ConfigOptions.ts";

 /*
 * It figures out “which LiveKit focus URL/alias the local user should use,”
@@ -46,20 +40,11 @@ interface Props {
  scope: ObservableScope;
  ownMembershipIdentity: CallMembershipIdentityParts;
  memberships$: Behavior<Epoch<CallMembership[]>>;
-  client: Pick<
-    MatrixClient,
-    "getDomain" | "baseUrl" | "_unstable_getRTCTransports"
-  > &
+  client: Pick<MatrixClient, "getDomain" | "_unstable_getRTCTransports"> &
    OpenIDClientParts;
  // Used by the jwt service to create the livekit room and compute the livekit alias.
  roomId: string;
-  forceJwtEndpoint: JwtEndpointVersion;
-  delayId$: Behavior<string | null>;
-}
-
-export enum JwtEndpointVersion {
-  Legacy = "legacy",
-  Matrix_2_0 = "matrix_2_0",
+  matrixRTCMode: MatrixRTCMode;
 }

 // TODO livekit_alias-cleanup
@@ -122,8 +107,7 @@ export const createLocalTransport$ = ({
  ownMembershipIdentity,
  client,
  roomId,
-  forceJwtEndpoint,
-  delayId$,
+  matrixRTCMode,
 }: Props): LocalTransport => {
  const logger = rootLogger.getChild("[LocalTransport]");

@@ -138,40 +122,36 @@ export const createLocalTransport$ = ({
    transportDiscovery.discoverPreferredTransport(),
  );

-  const preferredConfig$ = customLivekitUrl.value$
-    .pipe(
-      switchMap((customUrl) => {
-        if (customUrl) {
-          return of({
-            type: "livekit",
-            livekit_service_url: customUrl,
-          } as LivekitTransportConfig);
-        } else {
-          return discoveredTransport$;
-        }
-      }),
-    )
-    .pipe(
-      map((config) => {
-        if (!config) {
-          // Bubbled up from the preferredConfig$ observable.
-          throw new MatrixRTCTransportMissingError(client.getDomain() ?? "");
-        }
-        return config;
-      }),
-      distinctUntilChanged(areLivekitTransportsEqual),
-    );
+  const preferredConfig$ = customLivekitUrl.value$.pipe(
+    switchMap((customUrl) => {
+      if (customUrl) {
+        return of({
+          type: "livekit",
+          livekit_service_url: customUrl,
+        } as LivekitTransportConfig);
+      } else {
+        return discoveredTransport$;
+      }
+    }),
+    map((config) => {
+      if (!config) {
+        // Bubbled up from the preferredConfig$ observable.
+        throw new MatrixRTCTransportMissingError(client.getDomain() ?? "");
+      }
+      return config;
+    }),
+    distinctUntilChanged(areLivekitTransportsEqual),
+  );

-  const preferredTransport$ = combineLatest([preferredConfig$, delayId$]).pipe(
-    switchMap(async ([transport, delayId]) => {
+  const preferredTransport$ = preferredConfig$.pipe(
+    switchMap(async (transport) => {
      try {
        return await doOpenIdAndJWTFromUrl(
          transport,
-          forceJwtEndpoint,
+          matrixRTCMode,
          ownMembershipIdentity,
          roomId,
          client,
-          delayId ?? undefined,
          logger,
        );
      } catch (e) {
@@ -193,21 +173,7 @@ export const createLocalTransport$ = ({
      ),
      null,
    ),
-    active$: scope.behavior(
-      preferredTransport$.pipe(
-        // XXX: WORK AROUND due to a reconnection glitch.
-        // To remove when we have a proper way to refresh the delegation event ID without refreshing
-        // the whole credentials.
-        // We deliberately hide any changes to the SFU config because we
-        // do not want the app to reconnect whenever the JWT
-        // token changes due to us delegating a new delayed event. The
-        // initial SFU config for the transport is all the app needs.
-        distinctUntilChanged((prev, next) =>
-          areLivekitTransportsEqual(prev.transport, next.transport),
-        ),
-      ),
-      null,
-    ),
+    active$: scope.behavior(preferredTransport$, null),
  };
 };

@@ -219,25 +185,19 @@ export const createLocalTransport$ = ({
 *  use we don't want to risk any issues by re-using a token.
 *
 *  @param transport The transport to authenticate with.
- *  @param forceJwtEndpoint Whether to force the JWT endpoint to be used.
+ *  @param matrixRTCMode Whether to force the JWT endpoint to be used.
 *  @param membership The identity of the local member.
 *  @param roomId The room ID to use for the JWT.
 *  @param client The client to use for the OpenID token.
- *  @param delayId The delayId to use for the JWT.
 *
 *  @throws FailToGetOpenIdToken, NoMatrix2AuthorizationService
 */
 async function doOpenIdAndJWTFromUrl(
  transport: LivekitTransportConfig,
-  forceJwtEndpoint: JwtEndpointVersion,
+  matrixRTCMode: MatrixRTCMode,
  membership: CallMembershipIdentityParts,
  roomId: string,
-  client: Pick<
-    MatrixClient,
-    "getDomain" | "baseUrl" | "_unstable_getRTCTransports"
-  > &
-    OpenIDClientParts,
-  delayId?: string,
+  client: Pick<MatrixClient, "_unstable_getRTCTransports"> & OpenIDClientParts,
  logger?: Logger,
 ): Promise<LocalTransportWithSFUConfig> {
  const sfuConfig = await getSFUConfigWithOpenID(
@@ -245,11 +205,7 @@ async function doOpenIdAndJWTFromUrl(
    membership,
    transport.livekit_service_url,
    roomId,
-    {
-      forceJwtEndpoint: forceJwtEndpoint,
-      delayEndpointBaseUrl: client.baseUrl,
-      delayId,
-    },
+    { matrixRTCMode },
    logger,
  );
  return {
@@ -9,9 +9,30 @@ import { expect, test } from "vitest";
 import { type Observable, of, Subject, switchMap } from "rxjs";

 import { withTestScheduler } from "./test";
-import { filterBehavior, generateItems, pauseWhen } from "./observable";
+import { or$, filterBehavior, generateItems, pauseWhen } from "./observable";
 import { type Behavior } from "../state/Behavior";

+const yesNo = {
+  y: true,
+  n: false,
+};
+
+test("or$", () => {
+  withTestScheduler(({ behavior, expectObservable }) => {
+    const input1Marbles = "ny--n--";
+    const input2Marbles = "n-y--n-";
+    const input3Marbles = "n--y--n";
+    const outputMarbles = "nyyyyyn";
+    expectObservable(
+      or$(
+        behavior(input1Marbles, yesNo),
+        behavior(input2Marbles, yesNo),
+        behavior(input3Marbles, yesNo),
+      ),
+    ).toBe(outputMarbles, yesNo);
+  });
+});
+
 test("pauseWhen", () => {
  withTestScheduler(({ behavior, expectObservable }) => {
    const inputMarbles = " abcdefgh-i-jk-";
@@ -114,13 +114,11 @@ export function getValue<T>(state$: Observable<T>): T {
 }

 /**
- * Creates an Observable that has a value of true whenever all its inputs are
- * true.
- *
- * @public
+ * Creates an Observable that has a value of true whenever some of its inputs
+ * are true.
 */
-export function and$(...inputs: Observable<boolean>[]): Observable<boolean> {
-  return combineLatest(inputs, (...flags) => flags.every((flag) => flag));
+export function or$(...inputs: Observable<boolean>[]): Observable<boolean> {
+  return combineLatest(inputs, (...flags) => flags.some((flag) => flag));
 }

 /**
@@ -229,38 +227,6 @@ export function filterBehavior<T, S extends T>(
    );
 }

-/**
- * Maps a changing input value to an item whose lifetime is tied to a certain
- * computed key. The item may capture some dynamic data from the input.
- */
-export function generateItem<
-  Input,
-  Keys extends [unknown, ...unknown[]],
-  Data,
-  Item,
->(
-  name: string,
-  generator: (input: Input) => { keys: readonly [...Keys]; data: Data },
-  factory: (
-    scope: ObservableScope,
-    data$: Behavior<Data>,
-    ...keys: Keys
-  ) => Item,
-): OperatorFunction<Input, Item> {
-  return (input$) =>
-    input$.pipe(
-      generateItemsInternal(
-        name,
-        function* (input) {
-          yield generator(input);
-        },
-        factory,
-        (items) => items,
-      ),
-      map(([item]) => item),
-    );
-}
-
 function generateItemsInternal<
  Input,
  Keys extends [unknown, ...unknown[]],
@@ -174,7 +174,7 @@ export function getBasicCallViewModelEnvironment(
          setE2EEEnabled: async () => Promise.resolve(),
        }),
      connectionState$: constant(ConnectionState.Connected),
-      matrixRTCMode$: constant(MatrixRTCMode.Compatibility),
+      matrixRTCMode: MatrixRTCMode.Compatibility,
      ...callViewModelOptions,
    },
    handRaisedSubject$,
@@ -27,8 +27,6 @@ export default defineConfig((env) =>
            data: {
              matrix_rtc_session: {
                wait_for_key_rotation_ms: 5000,
-                delayed_leave_event_restart_ms: 4000,
-                delayed_leave_event_delay_ms: 18000,
              },
            },
          },