fix(calls): one delayed-event restart in flight per id, with a timeout (#318)

During a homeserver stall Element Call retries update_delayed_event every
2 s, and the host opened a new HTTP request each time: 12 pending in a
60 s stall, all landing together on recovery (404 x5, 429 x7). Share the
in-flight restart per delay id and abort it after 5 s.

Refs #318

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017PCb59uY3UKqDqt7B6hzd5

src/app/plugins/call/CallWidgetDriver.ts

@@ -28,7 +28,10 @@ import {
 } from 'matrix-js-sdk';
 import { getCallCapabilities } from './utils';
 import { downloadMedia, mxcUrlToHttp } from '../../utils/matrix';
+import { dedupeInFlight } from '../../utils/inFlight';
 
+/** A little longer than Element Call's own 2 s timeout for a restart. */
+const RESTART_TIMEOUT_MS = 5000;
 export class CallWidgetDriver extends WidgetDriver {
   private allowedCapabilities: Set<Capability>;
 
@@ -129,8 +132,18 @@ export class CallWidgetDriver extends WidgetDriver {
     await this.mx._unstable_cancelScheduledDelayedEvent(delayId);
   }
 
+  // [Gitea #318] While the homeserver is stalled, Element Call times out each
+  // restart locally after 2 s and asks again, so requests for the same delay
+  // id piled up and hit the server together on recovery (404s, then 429s).
+  // Share one in-flight restart per id, and give it a timeout of its own.
+  private readonly restartOnce = dedupeInFlight<unknown>();
+
   public async restartScheduledDelayedEvent(delayId: string): Promise<void> {
-    await this.mx._unstable_restartScheduledDelayedEvent(delayId);
+    await this.restartOnce(delayId, () =>
+      this.mx._unstable_restartScheduledDelayedEvent(delayId, {
+        localTimeoutMs: RESTART_TIMEOUT_MS,
+      }),
+    );
   }
 
   public async sendScheduledDelayedEvent(delayId: string): Promise<void> {

src/app/utils/inFlight.test.ts

@@ -0,0 +1,32 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { dedupeInFlight } from './inFlight';
+
+test('dedupeInFlight: one request per key while pending, a new one after (#318)', async () => {
+  const once = dedupeInFlight<number>();
+  let calls = 0;
+  let release!: () => void;
+  const gate = new Promise<void>((r) => {
+    release = r;
+  });
+  const run = async () => {
+    calls += 1;
+    await gate;
+    return calls;
+  };
+  const a = once('d1', run);
+  const b = once('d1', run);
+  const c = once('d2', run);
+  assert.equal(a, b);
+  release();
+  assert.deepEqual(await Promise.all([a, b, c]), [2, 2, 2]);
+  assert.equal(calls, 2);
+  await once('d1', run);
+  assert.equal(calls, 3, 'settled requests are not reused');
+});
+
+test('dedupeInFlight: a rejection clears the key', async () => {
+  const once = dedupeInFlight<void>();
+  await assert.rejects(once('k', () => Promise.reject(new Error('boom'))));
+  await once('k', () => Promise.resolve());
+});

src/app/utils/inFlight.ts

@@ -0,0 +1,14 @@
+/**
+ * Share one in-flight promise per key: callers that ask again while a request
+ * for the same key is still pending get that request instead of a new one.
+ */
+export function dedupeInFlight<T>(): (key: string, run: () => Promise<T>) => Promise<T> {
+  const pending = new Map<string, Promise<T>>();
+  return (key, run) => {
+    const existing = pending.get(key);
+    if (existing) return existing;
+    const p = run().finally(() => pending.delete(key));
+    pending.set(key, p);
+    return p;
+  };
+}