Version discovery spoke only hub.docker.com, and every other registry
got a shrug: updaterTagExists returned "no" and updaterRegistryTags
returned nothing. Five apps live off Hub — stoat and wireguard on
ghcr.io, bookstack and speedtest on lscr.io, invidious on quay.io — and
for all of them the updater reported "up to date" having never asked.
That is the same dishonesty as a scan that never ran: an absence of
evidence rendered as a clean bill of health.
There was never a barrier, only unwritten code. The standard
Distribution API needs one extra step: request, read the
WWW-Authenticate challenge, fetch a token from the realm it names,
retry. ghcr.io, quay.io and lscr.io all answer anonymously for public
images — lscr.io by pointing its realm at ghcr.io, quay.io by not
challenging at all.
Docker Hub deliberately keeps its own path. hub.docker.com returns tags
NEWEST-first, so the 100 it pages are the 100 that matter, and it draws
on a different budget from the pull limit — registry-1.docker.io
manifest reads count against the anonymous 100/hour that the updater
needs for actual pulls, and a ladder probes a tag per rung.
Tag LISTING off Hub is a weaker signal and the comment says so: /v2/
tags/list is lexical, not newest-first, and large repos cap the page, so
the newest release can legitimately be absent. Probing backfills it,
which is why the probe fallback added earlier matters more off Hub than
on it.
Verified against all four registries: existence probing correct on eight
cases including true negatives; stoat climbs v0.15.0 -> v0.15.1 through
ghcr.io, and correctly reports nothing above v0.15.1 — the same answer
as before, but now because it looked. Hub unregressed: matrix still
resolves v1.158.0 -> v1.159.0 and nextcloud still ladders 31 -> 32 33 34.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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