Bidirectional sync between a local directory and a Drive folder with
diff detection (new_local, new_remote, modified, unchanged) and
conflict resolution strategies (--on-conflict: remote-wins, local-wins,
keep-both, ask).
Key behaviors:
- Type conflict detection: hard-fail when local file vs remote non-file
or local directory vs remote file
- Keep-both: rename local with __lark_<hash> suffix, then pull remote;
occupied map includes localDirs to prevent suffix collision
- Local-wins partial-success: prefer returned file_token on upload failure
- Empty directory mirroring: pre-create local dirs on Drive via
drivePushWalkLocal before scope preflight
- Structured errors throughout (output.Errorf / output.ErrWithHint)
Includes unit tests and E2E tests (dry-run + live workflow).
