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.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(