fix(messaging,ios): fix an issue where the scene initializer could be called twice in latest Flutter versions

[Lyokone]

Description

Fix EXC_BAD_ACCESS crash on iOS when tapping a notification under UIScene lifecycle (FlutterImplicitEngineDelegate).

setupNotificationHandlingWithRemoteNotification: was called twice (from UIApplicationDidFinishLaunchingNotification + scene:willConnectToSession:), causing _originalNotificationCenterDelegate to point to self → infinite recursion on notification tap.

Added a guard so delegate/swizzler setup only runs once, while still allowing the second call to process the launch notification.

No test: requires a real push notification tap delivered by the OS under UIScene lifecycle — not possible from E2E or unit tests.

Related Issues

Fixes #18037

Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• My PR includes unit or integration tests for all changed/updated/fixed behaviors (See Contributor Guide).
• All existing and new tests are passing.
• I updated/added relevant documentation (doc comments with ///).
• The analyzer (melos run analyze) does not report any problems on my PR.
• I read and followed the Flutter Style Guide.
• I signed the CLA.
• I am willing to follow-up on review comments in a timely manner.

Breaking Change

• Yes, this is a breaking change.
• No, this is not a breaking change.

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[cdeil]

Our Flutter app also crashes because of this issue.

Terminating app due to uncaught exception 'NSInvalidArgumentException',
reason: '-[Runner.AppDelegate initialNotificationCallback]:
unrecognized selector sent to instance 0x102251780'

Coding agent is recommending to put this into the AppDelegate as workaround but I don't know if that's proper:

  // Required for firebase_messaging compatibility with Flutter 3.41+.
  // Without this, the plugin adds a donor method to AppDelegate that crashes
  // because `self` is the AppDelegate instead of the plugin instance.
  override func application(
    _ application: UIApplication,
    didReceiveRemoteNotification userInfo: [AnyHashable: Any],
    fetchCompletionHandler completionHandler: @escaping (UIBackgroundFetchResult) -> Void
  ) {
    super.application(application, didReceiveRemoteNotification: userInfo, fetchCompletionHandler: completionHandler)
  }

Could you please release a new version with this fix?