Stable twin of #1151.
The script here carried the identical defect: it computed `storage/events/active/<photo.path>` and fs.access'd it, which does not exist for external or reference rows. #1129 already landed on this branch, so the route was fixed and the script was the remaining half.
Resolution goes through ensureThumbnail, which stable already exports with the external branch intact. Also carried: videos skipped on every marker, skip-vs-generate asked from isThumbnailValid, and a nonzero exit when a photo could not be built.
Not carried: the responsive-tier backfill — THUMBNAIL_WIDTHS and ensureThumbnailAtWidth are #1095/#1109 and do not exist on this branch.
Merged with admin privileges: the author cannot self-approve.
Paul Nothaft
e46260ad07