fix(calls): hang up explicitly when answering another call while in one (#195)

Answering from the in-call banner is the only call-to-call switch path; it
started the new embed and let the atom dispose the old one, which just removed
the iframe — our m.call.member in the old room lingered ~17 s (until the
delayed leave expired), so everyone there still saw us in the call.

hangupAndWait moves out of LogoutDialog into plugins/call/hangup.ts and
handleAnswer now hangs up, waits for our membership to clear (bounded 4 s),
disposes the old embed itself (its HangupCall echo would otherwise land after
startCall and clear the NEW embed from the atom — seen in testing), then joins
the new call. Measured headless: old membership gone in 1 s, new call live
with both participants.

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

src/app/components/LogoutDialog.tsx

@@ -1,11 +1,10 @@
 import React, { forwardRef, useCallback } from 'react';
 import { Dialog, Header, config, Box, Text, Button, Spinner, color } from 'folds';
 import { useAtom } from 'jotai';
-import { MatrixClient } from 'matrix-js-sdk';
 import { AsyncStatus, useAsyncCallback } from '../hooks/useAsyncCallback';
 import { logoutClient } from '../../client/initMatrix';
 import { callEmbedAtom } from '../state/callEmbed';
-import { CallEmbed } from '../plugins/call';
+import { hangupCallAndWait } from '../plugins/call/hangup';
 import { useMatrixClient } from '../hooks/useMatrixClient';
 import { useModalStyle } from '../hooks/useModalStyle';
 import { useCrossSigningActive } from '../hooks/useCrossSigning';
@@ -20,27 +19,6 @@ import {
  * membership has actually been removed from the room, so the leave reaches
  * the homeserver before the client is stopped and the token is revoked.
  */
-const hangupAndWait = async (mx: MatrixClient, embed: CallEmbed): Promise<void> => {
-  const myUserId = mx.getUserId();
-  const myDeviceId = mx.getDeviceId();
-  const stillIn = (): boolean =>
-    mx.matrixRTC
-      .getRoomSession(embed.room)
-      .memberships.some((m) => m.sender === myUserId && m.deviceId === myDeviceId);
-  try {
-    await embed.hangup();
-  } catch {
-    // widget already gone — fall through to the wait/timeout
-  }
-  const deadline = Date.now() + 4000;
-  while (stillIn() && Date.now() < deadline) {
-    // eslint-disable-next-line no-await-in-loop
-    await new Promise((r) => {
-      setTimeout(r, 150);
-    });
-  }
-};
-
 type LogoutDialogProps = {
   handleClose: () => void;
 };
@@ -64,7 +42,7 @@ export const LogoutDialog = forwardRef<HTMLDivElement, LogoutDialogProps>(
         // membership (expires: 4 h) stays behind as a ghost participant and
         // everyone else sees you "in call" until it times out.
         if (callEmbed && callEmbed.joined && !callEmbed.disposed) {
-          await hangupAndWait(mx, callEmbed);
+          await hangupCallAndWait(mx, callEmbed);
           setCallEmbed(undefined);
         }
         await logoutClient(mx);