feat: VTT version control — snapshots, diff, restore
Backend:
- VttVersion model (vtt_version.py): immutable snapshot per job/lang/kind/version
- vtt_versioning service: create_version (atomic counter + GCS snapshot),
list_versions, get_version, restore_version, diff_versions (difflib line-level)
- routes_vtt_versions.py: GET /versions, GET /versions/{v}, GET /versions/diff,
POST /versions/{v}/restore (PRODUCTION/ADMIN only, overwrites live file + audit log)
- Hook create_version into update_job_vtt_content before each live-file overwrite
- Mongo indexes: unique (job_id, lang, kind, version) + (job_id, created_at)
Frontend:
- VttVersionSummary / VttVersionFull / VttDiffResponse types
- api.ts: listVttVersions, getVttVersion, diffVttVersions, restoreVttVersion
- VersionsTab.tsx: lang/kind switcher, version list with A/B compare buttons,
inline diff viewer (color-coded +/−), content viewer, restore with confirm dialog
- JobDetail.tsx: new "VTT Versions" tab wired to VersionsTab
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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