A URL copied from the browser gave us the route we never tried:
/backend-api/estuary/content?id=…&ts=496382&p=fs&cid=1&sig=…&v=0
Fetched with no cookies it returns 403 {"detail":"File stream access
denied."}, so the signature rides on the session rather than replacing it.
Every earlier probe lived under /backend-api/files/*; estuary/* is new
ground.
estuary_probe.py checks two things:
A. What /files/{id}/download hands back for a file that works. If its
download_url is an estuary URL, that endpoint is the minting step, and a
gizmo file's 403 is a refusal to mint — which is why no amount of
scoping helped.
B. Whether the estuary namespace exposes a route that serves a refused
file directly.
It also replays a pasted URL through the exporter's session, and says
plainly whether the id in that URL is one of the refused files — the two
captured so far were working images, so they showed the shape without
telling us whether the broken ones have a URL at all.
