fix: override cancelScheduledDelayedEvent/restart/send in CallWidgetDriver

The base WidgetDriver throws Failed to override function for these
methods. ClientWidgetApi routes update_delayed_event widget actions to
cancelScheduledDelayedEvent, restartScheduledDelayedEvent, or
sendScheduledDelayedEvent. Without these overrides every delayed-event
refresh from element-call fails, causing MembershipManager to drop the
call after retries.

Also make listenAction auto-call preventDefault so io.element.join and
other custom widget actions return success. Add set_always_on_screen
handler so element-call PiP requests are acknowledged.

src/app/plugins/call/CallEmbed.ts

@@ -12,6 +12,7 @@ import {
   IRoomEvent,
   IWidget,
   Widget,
+  WidgetApiFromWidgetAction,
   WidgetApiToWidgetAction,
   WidgetDriver,
 } from 'matrix-widget-api';
@@ -248,6 +249,10 @@ export class CallEmbed {
     this.disposables.push(
       this.listenAction(ElementWidgetActions.JoinCall, this.onCallJoined.bind(this)),
     );
+    // Acknowledge set_always_on_screen; we manage PiP ourselves so just return success
+    this.disposables.push(
+      this.listenAction(WidgetApiFromWidgetAction.UpdateAlwaysOnScreen, () => {}),
+    );
 
     // Populate the map of "read up to" events for this widget with the current event in every room.
     // This is a bit inefficient, but should be okay. We do this for all rooms in case the widget
@@ -460,7 +465,11 @@ export class CallEmbed {
   }
 
   public listenAction<T>(type: string, callback: (event: CustomEvent<T>) => void) {
-    return this.listenEvent(`action:${type}`, callback);
+    const wrapped = (ev: CustomEvent<T>) => {
+      ev.preventDefault();
+      callback(ev);
+    };
+    return this.listenEvent(`action:${type}`, wrapped);
   }
 
   public listenEvent<T>(type: string, callback: (event: T) => void) {

src/app/plugins/call/CallWidgetDriver.ts

@@ -148,6 +148,18 @@ export class CallWidgetDriver extends WidgetDriver {
     await client._unstable_updateDelayedEvent(delayId, action);
   }
 
+  public async cancelScheduledDelayedEvent(delayId: string): Promise<void> {
+    await this.mx._unstable_cancelScheduledDelayedEvent(delayId);
+  }
+
+  public async restartScheduledDelayedEvent(delayId: string): Promise<void> {
+    await this.mx._unstable_restartScheduledDelayedEvent(delayId);
+  }
+
+  public async sendScheduledDelayedEvent(delayId: string): Promise<void> {
+    await this.mx._unstable_sendScheduledDelayedEvent(delayId);
+  }
+
   public async sendToDevice(
     eventType: string,
     encrypted: boolean,