When state says you've left ongoing call, rejoin

When receiving a state change that says you are no longer a member of a
RTC session that you are actually still participating in, send another
state event to put yourself back in the session membership.

This can happen when an administrator overwrites your call membership
event (which is allowed even with MSC3757's restrictions on state), or
if your delayed disconnection event (via MSC4140) timed out before your
client could send a heartbeat to delay it further.

src/matrixrtc/MatrixRTCSession.ts

@@ -772,6 +772,14 @@ export class MatrixRTCSession extends TypedEventEmitter<MatrixRTCSessionEvent, M
         if (changed) {
             logger.info(`Memberships for call in room ${this.room.roomId} have changed: emitting`);
             this.emit(MatrixRTCSessionEvent.MembershipsChanged, oldMemberships, this.memberships);
+
+            if (this.isJoined() && !this.memberships.some(this.isMyMembership)) {
+                logger.warn("Missing own membership: force re-join");
+                // TODO: Should this be awaited? And is there anything to tell the focus?
+                this.triggerCallMembershipEventUpdate();
+                // TODO: Is this needed?
+                this.emit(MatrixRTCSessionEvent.JoinStateChanged, true);
+            }
         }
 
         if (this.manageMediaKeys && this.isJoined() && this.makeNewKeyTimeout === undefined) {
@@ -942,6 +950,7 @@ export class MatrixRTCSession extends TypedEventEmitter<MatrixRTCSessionEvent, M
     }
 
     private triggerCallMembershipEventUpdate = async (): Promise<void> => {
+        // TODO: Should this await on a shared promise?
         if (this.updateCallMembershipRunning) {
             this.needCallMembershipUpdate = true;
             return;
@@ -1030,7 +1039,6 @@ export class MatrixRTCSession extends TypedEventEmitter<MatrixRTCSessionEvent, M
                 const stateKey = this.makeMembershipStateKey(localUserId, localDeviceId);
                 const prepareDelayedDisconnection = async (): Promise<void> => {
                     try {
-                        // TODO: If delayed event times out, re-join!
                         const res = await resendIfRateLimited(() =>
                             this.client._unstable_sendDelayedStateEvent(
                                 this.room.roomId,