From 745772f6720d7cf5b86512976da36babed161be6 Mon Sep 17 00:00:00 2001
From: Timo K <toger5@hotmail.de>
Date: Tue, 20 Jan 2026 13:45:07 +0100
Subject: [PATCH] Fix rejoin EC crash Due to a duplcaited key (the key not
 being specific enough)

---
 playwright/spa-call-sticky.spec.ts            | 60 ++++++++++++++++---
 .../remoteMembers/MatrixLivekitMembers.ts     | 14 ++++-
 2 files changed, 62 insertions(+), 12 deletions(-)

diff --git a/playwright/spa-call-sticky.spec.ts b/playwright/spa-call-sticky.spec.ts
index ea2355d1..246b4a73 100644
--- a/playwright/spa-call-sticky.spec.ts
+++ b/playwright/spa-call-sticky.spec.ts
@@ -5,15 +5,21 @@ SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
 Please see LICENSE in the repository root for full details.
 */
 
-import { expect, type Page, test, type Request } from "@playwright/test";
+import {
+  expect,
+  type Page,
+  test,
+  type Request,
+  type Browser,
+} from "@playwright/test";
 
 import { SpaHelpers } from "./spa-helpers";
 
-test("One to One call using matrix rtc 2.0 aka sticky events", async ({
-  browser,
-  page,
-  browserName,
-}) => {
+async function setupTwoUserSpaCall(
+  browser: Browser,
+  page: Page,
+  browserName: string,
+): Promise<{ guestPage: Page }> {
   test.skip(
     browserName === "firefox",
     "The is test is not working on firefox CI environment. No mic/audio device inputs so cam/mic are disabled",
@@ -63,13 +69,49 @@ test("One to One call using matrix rtc 2.0 aka sticky events", async ({
     "Pevara",
     "2_0",
   );
+  // Assert both sides have sent sticky membership events
+  expect(androlHasSentStickyEvent).toEqual(true);
+  expect(pevaraHasSentStickyEvent).toEqual(true);
+
+  return { guestPage };
+}
+
+test("One to One call using matrix rtc 2.0 aka sticky events", async ({
+  browser,
+  page,
+  browserName,
+}) => {
+  const { guestPage } = await setupTwoUserSpaCall(browser, page, browserName);
+
+  await SpaHelpers.expectVideoTilesCount(page, 2);
+  await SpaHelpers.expectVideoTilesCount(guestPage, 2);
+});
+
+// This issue occurs when a member leave but does not clean up their sticky event.
+// If they rejoin they will use a new stickye key (stickyKey = member.id = UUID())
+// We end up with two memberships with the same user and device id. This previously
+// was a impossible case since that would be the same state event. Now its possible.
+// We need to ALWAYS key by userId, deviceId and member.id. This test checks that.
+test("One to One rejoin after improper leave does not crash EC", async ({
+  browser,
+  page,
+  browserName,
+}) => {
+  const { guestPage } = await setupTwoUserSpaCall(browser, page, browserName);
 
   await SpaHelpers.expectVideoTilesCount(page, 2);
   await SpaHelpers.expectVideoTilesCount(guestPage, 2);
 
-  // Assert both sides have sent sticky membership events
-  expect(androlHasSentStickyEvent).toEqual(true);
-  expect(pevaraHasSentStickyEvent).toEqual(true);
+  await guestPage.reload();
+  await expect(guestPage.getByTestId("lobby_joinCall")).toBeVisible();
+
+  // Check if rejoining with the same browser context (device) breaks EC.
+  // This has happened on versions that do not consider the member.id as part of the key for a media tile.
+  await guestPage.getByTestId("lobby_joinCall").click();
+
+  // We cannot use the `expectVideoTilesCount` helper here since one of them is expected to show waiting for media
+  await expect(page.getByTestId("videoTile")).toHaveCount(3);
+  await expect(guestPage.getByTestId("videoTile")).toHaveCount(2);
 });
 
 function isStickySend(url: string): boolean {
diff --git a/src/state/CallViewModel/remoteMembers/MatrixLivekitMembers.ts b/src/state/CallViewModel/remoteMembers/MatrixLivekitMembers.ts
index c98cb581..b54a50df 100644
--- a/src/state/CallViewModel/remoteMembers/MatrixLivekitMembers.ts
+++ b/src/state/CallViewModel/remoteMembers/MatrixLivekitMembers.ts
@@ -111,15 +111,23 @@ export function createMatrixLivekitMembers$({
               : null;
 
             yield {
-              keys: [membership.userId, membership.deviceId],
+              // This could also just be the memberId without the other fields.
+              // In theory we should never have the same memberId for different userIds (they are UUIDs)
+              // This still makes us resilient agains someone who intentionally tries to use the same memberId.
+              // If they want to do this they would now need to also use the same sender which is impossible.
+              keys: [
+                membership.userId,
+                membership.deviceId,
+                membership.memberId,
+              ],
               data: { membership, participant, connection },
             };
           }
         },
         // Each update where the key of the generator array do not change will result in updates to the `data$` observable in the factory.
-        (scope, data$, userId, deviceId) => {
+        (scope, data$, userId, deviceId, memberId) => {
           logger.debug(
-            `Generating member for livekitIdentity: ${data$.value.membership.rtcBackendIdentity}, userId:deviceId: ${userId}${deviceId}`,
+            `Generating member for livekitIdentity: ${data$.value.membership.rtcBackendIdentity},keys userId:deviceId:memberId ${userId}:${deviceId}:${memberId}`,
           );
           const { participant$, ...rest } = scope.splitBehavior(data$);
           // will only get called once per `participantId, userId` pair.