Historical Video Thumbnail Cache Recovery
Previously uploaded Bilibili covers were still intact; complete response ETags and versioned thumbnail proxy URLs now make existing browsers discard cached empty covers without requiring another upload.
# Historical Video Thumbnail Cache Recovery
The manually uploaded covers for older Bilibili videos remain intact in the database, and every public thumbnail endpoint returns a valid image. This fix addresses cached empty covers in existing browsers.
## Cause and recovery
- The previous `/api/videos` ETag was derived only from video-row timestamps. When thumbnail interpretation changed without a database edit, browsers received 304 and reused the pre-fix response with empty cover fields.
- Video-list and single-video ETags now derive from the complete public representation, so changes to cover URLs, dimensions, categories, or other public fields produce a new cache identity.
- Same-origin proxy URLs for uploaded covers now carry the video update version. Historical empty caches are bypassed immediately, and later cover replacements cannot remain stuck on an older image.
## Verification
All 11 historical Bilibili covers on the live site returned valid JPEG responses and rendered in a clean browser profile. The recovery neither rewrites the stored cover data nor requires another admin upload.
