Add support for a grace period for /sync (aka homeserver disconnected) interruptions

config/config.sample.json

@@ -12,6 +12,7 @@
     "feature_use_device_session_member_events": true
   },
   "ssla": "https://static.element.io/legal/element-software-and-services-license-agreement-uk-1.pdf",
+  "sync_disconnect_grace_period_ms": 60000,
   "matrix_rtc_session": {
     "wait_for_key_rotation_ms": 3000,
     "membership_event_expiry_ms": 180000000,

src/config/ConfigOptions.ts

@@ -97,6 +97,13 @@ export interface ConfigOptions {
     enable_video?: boolean;
   };
 
+  /**
+   * Grace period in milliseconds to wait before reporting the sync loop as disconnected.
+   * This allows brief sync interruptions without triggering a reconnection message.
+   * Default is 60000ms (60 seconds). Set to 0 to disable the grace period.
+   */
+  sync_disconnect_grace_period_ms?: number;
+
   /**
    * These are low level options that are used to configure the MatrixRTC session.
    * Take care when changing these options.
@@ -168,5 +175,6 @@ export const DEFAULT_CONFIG: ResolvedConfigOptions = {
   features: {
     feature_use_device_session_member_events: true,
   },
+  sync_disconnect_grace_period_ms: 60000,
   ssla: "https://static.element.io/legal/element-software-and-services-license-agreement-uk-1.pdf",
 };

src/state/CallViewModel/CallViewModel.ts

@@ -83,6 +83,7 @@ import { E2eeType } from "../../e2ee/e2eeType";
 import { MatrixKeyProvider } from "../../e2ee/matrixKeyProvider";
 import { type MuteStates } from "../MuteStates";
 import { getUrlParams, HeaderStyle } from "../../UrlParams";
+import { Config } from "../../config/Config";
 import { type ProcessorState } from "../../livekit/TrackProcessorContext";
 import { ElementWidgetActions, widget } from "../../widget";
 import {
@@ -536,6 +537,7 @@ export function createCallViewModel$(
       scope,
       client,
       matrixRTCSession,
+      Config.get().sync_disconnect_grace_period_ms,
     ),
     muteStates,
     joinMatrixRTC: (transport: LivekitTransportConfig) => {

src/state/CallViewModel/localMember/HomeserverConnected.test.ts

@@ -96,19 +96,20 @@ describe("createHomeserverConnected$", () => {
 
   // LLM generated test cases. They are a bit overkill but I improved the mocking so it is
   // easy enough to read them so I think they can stay.
+  // Note: gracePeriodMs is set to 0 to avoid debouncing delays in tests
   it("is false when sync state is not Syncing", () => {
-    const hsConnected = createHomeserverConnected$(scope, client, session);
+    const hsConnected = createHomeserverConnected$(scope, client, session, 0);
     expect(hsConnected.combined$.value).toBe(false);
   });
 
   it("remains false while membership status is not Connected even if sync is Syncing", () => {
-    const hsConnected = createHomeserverConnected$(scope, client, session);
+    const hsConnected = createHomeserverConnected$(scope, client, session, 0);
     client.setSyncState(SyncState.Syncing);
     expect(hsConnected.combined$.value).toBe(false); // membership still disconnected
   });
 
   it("is false when membership status transitions to Connected but ProbablyLeft is true", () => {
-    const hsConnected = createHomeserverConnected$(scope, client, session);
+    const hsConnected = createHomeserverConnected$(scope, client, session, 0);
     // Make sync loop OK
     client.setSyncState(SyncState.Syncing);
     // Indicate probable leave before connection
@@ -118,7 +119,7 @@ describe("createHomeserverConnected$", () => {
   });
 
   it("becomes true only when all three conditions are satisfied", () => {
-    const hsConnected = createHomeserverConnected$(scope, client, session);
+    const hsConnected = createHomeserverConnected$(scope, client, session, 0);
     // 1. Sync loop connected
     client.setSyncState(SyncState.Syncing);
     expect(hsConnected.combined$.value).toBe(false); // not yet membership connected
@@ -128,7 +129,7 @@ describe("createHomeserverConnected$", () => {
   });
 
   it("drops back to false when sync loop leaves Syncing", () => {
-    const hsConnected = createHomeserverConnected$(scope, client, session);
+    const hsConnected = createHomeserverConnected$(scope, client, session, 0);
     // Reach connected state
     client.setSyncState(SyncState.Syncing);
     session.setMembershipStatus(Status.Connected);
@@ -140,7 +141,7 @@ describe("createHomeserverConnected$", () => {
   });
 
   it("drops back to false when membership status becomes disconnected", () => {
-    const hsConnected = createHomeserverConnected$(scope, client, session);
+    const hsConnected = createHomeserverConnected$(scope, client, session, 0);
     client.setSyncState(SyncState.Syncing);
     session.setMembershipStatus(Status.Connected);
     expect(hsConnected.combined$.value).toBe(true);
@@ -150,7 +151,7 @@ describe("createHomeserverConnected$", () => {
   });
 
   it("drops to false when ProbablyLeft is emitted after being true", () => {
-    const hsConnected = createHomeserverConnected$(scope, client, session);
+    const hsConnected = createHomeserverConnected$(scope, client, session, 0);
     client.setSyncState(SyncState.Syncing);
     session.setMembershipStatus(Status.Connected);
     expect(hsConnected.combined$.value).toBe(true);
@@ -160,7 +161,7 @@ describe("createHomeserverConnected$", () => {
   });
 
   it("recovers to true if ProbablyLeft becomes false again while other conditions remain true", () => {
-    const hsConnected = createHomeserverConnected$(scope, client, session);
+    const hsConnected = createHomeserverConnected$(scope, client, session, 0);
     client.setSyncState(SyncState.Syncing);
     session.setMembershipStatus(Status.Connected);
     expect(hsConnected.combined$.value).toBe(true);
@@ -174,7 +175,7 @@ describe("createHomeserverConnected$", () => {
   });
 
   it("composite sequence reflects each individual failure reason", () => {
-    const hsConnected = createHomeserverConnected$(scope, client, session);
+    const hsConnected = createHomeserverConnected$(scope, client, session, 0);
 
     // Initially false (sync error + disconnected + not probably left)
     expect(hsConnected.combined$.value).toBe(false);

src/state/CallViewModel/localMember/HomeserverConnected.ts

@@ -12,9 +12,11 @@ import {
   type MatrixRTCSession,
 } from "matrix-js-sdk/lib/matrixrtc";
 import { ClientEvent, type MatrixClient, SyncState } from "matrix-js-sdk";
-import { fromEvent, startWith, map, tap, type Observable } from "rxjs";
+import { fromEvent, startWith, map, tap, type Observable, debounceTime } from "rxjs";
 import { logger as rootLogger } from "matrix-js-sdk/lib/logger";
 
+import { Config } from "../../../config/Config";
+
 import { type ObservableScope } from "../../ObservableScope";
 import { type Behavior } from "../../Behavior";
 import { and$ } from "../../../utils/observable";
@@ -35,21 +37,29 @@ export interface HomeserverConnected {
  * for the purposes of a MatrixRTC session.
  *
  * Becomes FALSE if ANY sub-condition is fulfilled:
- * 1. Sync loop is not in SyncState.Syncing
+ * 1. Sync loop is not in SyncState.Syncing (after grace period)
  * 2. membershipStatus !== Status.Connected
  * 3. probablyLeft === true
+ *
+ * @param gracePeriodMs - Grace period in milliseconds to wait before reporting sync disconnect.
+ *                        If not provided, uses the config value (default 60000ms).
  */
 export function createHomeserverConnected$(
   scope: ObservableScope,
   client: NodeStyleEventEmitter & Pick<MatrixClient, "getSyncState">,
   matrixRTCSession: NodeStyleEventEmitter &
     Pick<MatrixRTCSession, "membershipStatus" | "probablyLeft">,
+  gracePeriodMs?: number,
 ): HomeserverConnected {
+  // Get grace period from parameter or config (default 60000ms)
+  const graceMs = gracePeriodMs ?? Config.get().sync_disconnect_grace_period_ms ?? 60000;
+
   const syncing$ = (
     fromEvent(client, ClientEvent.Sync) as Observable<[SyncState]>
   ).pipe(
     startWith([client.getSyncState()]),
     map(([state]) => state === SyncState.Syncing),
+    debounceTime(graceMs),
   );
 
   const rtsSession$ = scope.behavior<Status>(