fix: migration

[pwltr]

Summary of Fixes

Bug 1: Migration completion not checked during restore

Problem: After migration, users should only use VSS backups, but restoreFromMostRecentBackup() didn't check if migration was completed.

Fix: Added a check at the start of restoreFromMostRecentBackup() - if isMigrationCompleted is true, only use VSS backups and skip RN backup checks entirely.

Bug 2: Migration flag cleared during wipe

Problem: AppReset.wipe() clears all UserDefaults (line 37), which removes the rnMigrationCompleted flag. After wipe+restore, the app would check RN backups again.

Fix: Preserve the rnMigrationCompleted flag before wiping UserDefaults, then restore it after wipe. This ensures that if a user migrated before, they'll only use VSS backups after restore.

Bug 3: Aggressive fallback to RN when VSS timestamp unavailable

Problem: If VSS timestamp fetch failed (returned nil), the code would immediately fall back to RN backup, even though VSS backup might exist.

Fix: Improved the logic to prefer VSS even when timestamp is unavailable, with better logging to help debug timestamp fetch issues.

Changes Made

1. MigrationsService.swift: Added isMigrationCompleted property and markMigrationCompleted() method
2. AppScene.swift:
   • Added early return if migration was completed (only use VSS)
   • Improved logging for backup selection
   • Better handling when VSS timestamp is unavailable
3. AppReset.swift: Preserve rnMigrationCompleted flag during wipe

Testing Recommendations

1. Test scenario: User migrates from RN → uses native app → wipes → restores
   • Should only use VSS backup, not RN backup
2. Test scenario: User migrates from RN → wipes → restores (no VSS backup yet)
   • Should use RN backup as fallback
3. Test scenario: Fresh install (no migration) → restore
   • Should compare timestamps correctly

The fix ensures that once a user has migrated from RN, they'll always use VSS backups for restores, preventing the issue of restoring stale RN channel data.