diff --git a/.github/workflows/e2e.yml b/.github/workflows/e2e.yml
index c77482c..27e280d 100644
--- a/.github/workflows/e2e.yml
+++ b/.github/workflows/e2e.yml
@@ -10,8 +10,13 @@ on:
   workflow_dispatch:
 
 concurrency:
-  group: e2e-${{ github.ref }}
-  cancel-in-progress: true
+  # Repo-wide mutex: every E2E run shares one Supabase project, and concurrent
+  # runs race each other's beforeAll cleanupOldMessages hooks (run 25769955636
+  # on 2026-05-13 was cancelled at 60 min after PR #88's run, started 3 min
+  # later, wiped its data). Serialize across all refs; do not cancel a running
+  # job to make room for a queued one.
+  group: e2e-supabase-${{ github.repository }}
+  cancel-in-progress: false
 
 env:
   NEXT_PUBLIC_SUPABASE_URL: ${{ vars.NEXT_PUBLIC_SUPABASE_URL }}
diff --git a/tests/e2e/messaging/encrypted-messaging.spec.ts b/tests/e2e/messaging/encrypted-messaging.spec.ts
index adba5ea..97777f5 100644
--- a/tests/e2e/messaging/encrypted-messaging.spec.ts
+++ b/tests/e2e/messaging/encrypted-messaging.spec.ts
@@ -663,6 +663,7 @@ test.describe('Encrypted Messaging Flow', () => {
       .first()
       .evaluate((el) => {
         el.scrollTop = 0;
+        el.dispatchEvent(new Event('scroll', { bubbles: true }));
       });
 
     // Look for "Load More" button
diff --git a/tests/e2e/messaging/messaging-scroll.spec.ts b/tests/e2e/messaging/messaging-scroll.spec.ts
index d2e1791..5d77bd5 100644
--- a/tests/e2e/messaging/messaging-scroll.spec.ts
+++ b/tests/e2e/messaging/messaging-scroll.spec.ts
@@ -232,9 +232,14 @@ test.describe('Messaging Scroll - User Story 2: Scroll Through Messages', () =>
     );
     const initialInputBox = await messageInput.boundingBox();
 
-    // Scroll up in the message thread
+    // Scroll up in the message thread.
+    // WebKit does not always fire the scroll event for programmatic scrollTop
+    // assignments. Dispatch it explicitly so React listeners (e.g.,
+    // MessageThread's handleScroll at MessageThread.tsx:194) run reliably
+    // across browsers.
     await messageThread.evaluate((el) => {
       el.scrollTop = 0;
+      el.dispatchEvent(new Event('scroll', { bubbles: true }));
     });
 
     // Wait for scroll to complete
@@ -274,6 +279,7 @@ test.describe('Messaging Scroll - User Story 3: Jump to Bottom Button', () => {
     // Scroll up more than 500px to trigger button
     await messageThread.evaluate((el) => {
       el.scrollTop = Math.max(0, el.scrollHeight - el.clientHeight - 600);
+      el.dispatchEvent(new Event('scroll', { bubbles: true }));
     });
 
     await waitForUIStability(page);
@@ -320,6 +326,7 @@ test.describe('Messaging Scroll - User Story 3: Jump to Bottom Button', () => {
     // Scroll up to trigger button
     await messageThread.evaluate((el) => {
       el.scrollTop = 0;
+      el.dispatchEvent(new Event('scroll', { bubbles: true }));
     });
 
     await waitForUIStability(page);