Data loss: update recreated ~/.local/share/opencode and did not migrate legacy sessions

Summary

After an OpenCode update (storage moved to a SQLite database, opencode.db), the entire ~/.local/share/opencode data directory was recreated and all previously saved session history was lost. The legacy JSON storage/ directory no longer exists and was not imported into the new database.

Environment

• OS: macOS (Apple Silicon, arm64)
• Storage format observed: SQLite (opencode.db, -wal, -shm)
• Date of incident: 2026-06-29

What happened

1. UI changed after an update (new storage layout).
2. All contents of ~/.local/share/opencode were timestamped to the moment of the update (no older files remained).
3. New opencode.db contained only the single session created post-update.
4. No legacy storage/session/*.json directory existed anywhere on disk.
5. Logs contained no record of a data-migration/import step.
6. Config (~/.config/opencode/opencode.json), plugins, and skills were untouched — only session history under ~/.local/share/opencode was lost.

Expected behavior

The update/migration should import existing JSON sessions into the new SQLite database, or preserve the legacy storage/ directory, rather than recreating the data directory and discarding prior session history.

Impact

Irrecoverable loss of prior conversation/session history for users without an independent backup (no Time Machine / snapshots).

Suggested fixes

• Detect and migrate legacy storage/ data into opencode.db on first run of the new version.
• If migration is not possible, move (not delete) the legacy directory to a *.bak path and log it.
• Emit an explicit log line documenting the migration outcome.