metadata_diff found the discriminator. Every refused image carries
use_case="gizmo" — ChatGPT's name for Projects and custom GPTs — while
everything that downloads is image_gen or multimodal. All are state=ready,
so nothing is damaged: the plain /files/{id}/download endpoint just will
not serve a project-scoped file.
Second clue: all 11 were created 2026-07-14 within minutes of each other,
yet appear in conversations dated 2025-11 through 2026-08, several
predating their own creation_time. Something on July 14 re-created them as
gizmo-scoped copies and repointed the conversations — which is also why
the losses start in July. Not a policy change, an event.
gizmo_download_probe.py dumps the raw conversation part carrying one of
these assets (it may simply name the scope the download wants) and then
tries the plausible calls — gizmo_id/conversation_id query params, a
/gizmos/{id}/files path, a project Referer. A 200 is the fix.
