GTM preview URL is not applied on UIScene cold start Body

[mmyha]

Description

After migrating our Flutter iOS app to the UIScene lifecycle, Mobile GTM Preview no longer works on cold start.

The preview URL is correctly delivered to:

scene(_:willConnectTo:options:)


and exists in connectionOptions.urlContexts.
We forward it using the documented API:
Analytics.handleOpen(context.url)
GTM logs that it processed the URL, but it still loads the saved container instead of the preview container.

• Actual behavior

GoogleTagManager info: Loading container: GTM-XXXX
GoogleTagManager info: Attempting to load saved version of container GTM-XXXX
GoogleTagManager info: processing URL: tagmanager.c.<bundle-id>://preview/...

• Expected behavior

GoogleTagManager info: Attempting to load preview container for GTM-XXXX

Workaround
Calling the private API +[TAGContainerLoader processURL:] before GTM container initialization makes the preview container load correctly.
We do not want to depend on this private API.

Environment
GoogleTagManager: 9.2.0
FirebaseAnalytics / GoogleAppMeasurement: 12.9.0
Flutter: 3.41.4
Xcode: 16.4
iOS: 18.5
Lifecycle: UIScene

Flutter integration details:

• AppDelegate subclasses FlutterAppDelegate and implements FlutterImplicitEngineDelegate.
• SceneDelegate subclasses FlutterSceneDelegate.
• UIApplicationSceneManifest in Info.plist explicitly specifies the app's SceneDelegate, which subclasses FlutterSceneDelegate.
• Flutter plugins are registered through GeneratedPluginRegistrant in didInitializeImplicitFlutterEngine(_:).
• Firebase is initialized from Dart using FlutterFire:

Question
What is the supported public way to process a Mobile GTM preview URL before container loading during a UIScene cold start?