fix(call): actually resolve .well-known rtc_foci for MSC4515 — SDK cache is empty at runtime

81a6d9c9 wired getRtcTransports() but its .well-known fallback read
mx.getClientWellKnown(), which the SDK only populates when the client
is started with clientWellKnownPollPeriod — cinny never sets it, so on
the live client the fallback returned [] and calls still failed with
MISSING_MATRIX_RTC_TRANSPORT after deploy. (The unit test faked a
populated cache and hid this.)

The driver now fetches the client .well-known itself, once, via
AutoDiscovery.getRawClientConfig(domain) — the same resolver Element
Call used before 0.22 — and only when the SDK has nothing cached. Test
added for the uncached path (asserts a single fetch); verified the
resolver returns the livekit focus for matrix.lotusguild.org.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/app/plugins/call/CallWidgetDriver.rtcTransports.test.ts

@@ -1,6 +1,7 @@
 import { test } from 'node:test';
 import assert from 'node:assert/strict';
 import type { MatrixClient } from 'matrix-js-sdk';
+import { AutoDiscovery } from 'matrix-js-sdk';
 import { CallWidgetDriver } from './CallWidgetDriver';
 
 // MSC4515: Element Call (widget mode) asks the host for RTC transports. Without a
@@ -17,6 +18,7 @@ function fakeClient(opts: {
       return opts.serverTransports ?? [];
     },
     getClientWellKnown: () => opts.wellKnown,
+    getDomain: () => 'example.org',
   } as unknown as MatrixClient;
 }
 
@@ -40,13 +42,43 @@ test('getRtcTransports falls back to .well-known rtc_foci when the endpoint 404s
   assert.deepEqual(r.rtc_transports, [focus]);
 });
 
+test('getRtcTransports fetches .well-known itself when the SDK has nothing cached (the live cinny case)', async () => {
+  // cinny never sets clientWellKnownPollPeriod, so getClientWellKnown() is undefined
+  // at runtime; the driver must resolve it via AutoDiscovery instead.
+  const orig = AutoDiscovery.getRawClientConfig;
+  let calls = 0;
+  AutoDiscovery.getRawClientConfig = async () => {
+    calls += 1;
+    return { 'org.matrix.msc4143.rtc_foci': [focus] } as never;
+  };
+  try {
+    const driver = new CallWidgetDriver(
+      fakeClient({ serverTransports: new Error('404'), wellKnown: undefined }),
+      '!r:x',
+    );
+    const r1 = await driver.getRtcTransports();
+    const r2 = await driver.getRtcTransports();
+    assert.deepEqual(r1.rtc_transports, [focus]);
+    assert.deepEqual(r2.rtc_transports, [focus]);
+    assert.equal(calls, 1, 'well-known is fetched once per driver');
+  } finally {
+    AutoDiscovery.getRawClientConfig = orig;
+  }
+});
+
 test('getRtcTransports returns an empty list when nothing is advertised', async () => {
-  const driver = new CallWidgetDriver(
-    fakeClient({ serverTransports: [], wellKnown: { 'm.homeserver': {} } }),
-    '!r:x',
-  );
-  const r = await driver.getRtcTransports();
-  assert.deepEqual(r.rtc_transports, []);
+  const orig = AutoDiscovery.getRawClientConfig;
+  AutoDiscovery.getRawClientConfig = async () => ({ 'm.homeserver': {} }) as never;
+  try {
+    const driver = new CallWidgetDriver(
+      fakeClient({ serverTransports: [], wellKnown: { 'm.homeserver': {} } }),
+      '!r:x',
+    );
+    const r = await driver.getRtcTransports();
+    assert.deepEqual(r.rtc_transports, []);
+  } finally {
+    AutoDiscovery.getRawClientConfig = orig;
+  }
 });
 
 test('the MSC4515 capability is granted to the call widget', async () => {

src/app/plugins/call/CallWidgetDriver.ts

@@ -24,6 +24,7 @@ import {
   type StateEvents,
   type TimelineEvents,
   MatrixClient,
+  AutoDiscovery,
 } from 'matrix-js-sdk';
 import { getCallCapabilities } from './utils';
 import { downloadMedia, mxcUrlToHttp } from '../../utils/matrix';
@@ -33,6 +34,9 @@ export class CallWidgetDriver extends WidgetDriver {
 
   private readonly mx: MatrixClient;
 
+  // Memoised client .well-known fetch for getRtcTransports (MSC4515).
+  private wellKnownPromise: Promise<unknown> | undefined;
+
   public constructor(
     mx: MatrixClient,
     private inRoomId: string,
@@ -303,9 +307,22 @@ export class CallWidgetDriver extends WidgetDriver {
     } catch {
       // 404 / M_UNRECOGNIZED on homeservers without MSC4143 — fall through.
     }
-    const wellKnown = this.mx.getClientWellKnown() as
+    // The SDK only caches the client .well-known when started with
+    // `clientWellKnownPollPeriod`, which we don't set — so getClientWellKnown()
+    // is normally undefined here. Fetch it ourselves (once per driver) via the
+    // SDK's own resolver; this is exactly what Element Call did pre-0.22.
+    let wellKnown = this.mx.getClientWellKnown() as
       | { 'org.matrix.msc4143.rtc_foci'?: unknown }
       | undefined;
+    if (!wellKnown?.['org.matrix.msc4143.rtc_foci']) {
+      const domain = this.mx.getDomain();
+      if (domain) {
+        if (!this.wellKnownPromise) {
+          this.wellKnownPromise = AutoDiscovery.getRawClientConfig(domain).catch(() => ({}));
+        }
+        wellKnown = (await this.wellKnownPromise) as typeof wellKnown;
+      }
+    }
     const foci = wellKnown?.['org.matrix.msc4143.rtc_foci'];
     const transports = Array.isArray(foci)
       ? (foci.filter(