Refactor: Message Synchronization

🎯The objective

The goal of this project is to automatically fetch messages from the server when the user expects this to happen.

• When opening a folder for viewing
• When scrolling down the message list and reaching the end of the downloaded messages

🎒Resources

ℹ️ List all relevant resources like BugZilla meta bugs, Figma files, Notion links and other files.

• https://github.com/thunderbird/thunderbird-android/issues/8252

🦮Rules of the Road

🟢In Scope

• Find and implement synchronization related quick wins that would increase perception of stability for users
• Revise internal database to make it easier (TBD define) to synchronize messages with the remote server
  • Consider alignment with iOS database
  • Consider encryption and data safety
• Create KMP module with SQLDelight or Exposed that allows structured access to the database (do a spike to determine the right path forward). Likely we won't use the ORM version, but instead raw database access.
• Add a KMP module that builds a layer on top to abstract the actual queries into the email operations we need
• Migration mechanism to support changes to the new database
• Develop a strategy to move from old to new database model - this is a critical component, make sure we provide mitigations for dataloss.
• Various refactoring to adapt TfA to use the new database. This will likely be a substantial amount of work.
  • Move away from key/value store to a more relational model. Existing code around message list/compose will be difficult here.
  • TBD define this more closely after the first spike
• Elaborate testing strategy to minimize dataloss risks

🔴Out of Scope

Technical Considerations

• Consider writing an exporter for email before we roll out the new database to production, this way we can pre-empt any database dataloss by asking users to backup.