Fix Messaging Module in My Vibe-Coded Flutter App

I have a Flutter mobile app that was mostly created using AI-assisted/vibe coding. The app is working, but the messaging module has several problems. Current issues: • • • • • Messages sometimes remain stuck on “sending” New messages do not appear for the other user in real time Some messages appear twice after reopening the chat The unread message count is not updating correctly The chat list sometimes shows the old last message The backend uses Firebase Authentication and Cloud Firestore. I only need the messaging module checked and fixed. Please do not change the design or other parts of the application. I will provide the complete source code as a ZIP file after hiring. Please apply only if you have experience with: • • • • Flutter and Dart Firebase Firestore Real-time chat systems Debugging AI-generated or poorly structured Flutter code