Sync between devices

[ITechGeek81]

Given any thoughts about syncing between devices? Maybe make it so all the data can be synced over a service like SyncThing or Resilio Sync?

So my same setup is accessible across my phone and laptop. And potentially you could host a cloud service to generate some extra revenue to support development.

[farfromexact]

Syncthing or Resilio Sync could be a good first experiment, but I would avoid syncing a live database file between the phone and laptop. Concurrent SQLite or JSON writes can produce last-writer-wins data loss even when the sync tool reports that both files were transferred successfully.

A safer architecture is to separate the data model from the transport:

1. Keep a stable export format with IDs, timestamps, and schema version.
2. Add an explicit import/export or sync folder first.
3. Represent changes as append-only records or per-item files so conflicts can be detected.
4. Merge by stable item ID, not by filename or device clock alone.
5. Surface conflicts to the user instead of silently choosing one copy.

That would let Syncthing work as a privacy-friendly transport without tying Kai to one hosted service. A hosted backend could be added later behind the same sync interface, with authentication and end-to-end encryption handled separately.

For a first milestone, I would support one-way export and import plus a dry-run conflict report. Once the merge rules are proven, bidirectional sync becomes much less risky. The most important design decision is whether Kai's data is append-only, editable, or includes ordering/recurrence; those fields determine whether simple last-write-wins is acceptable or whether per-field merge metadata is needed.