[ci-maintainer] publish-iso-groups nightly fails: marlin/flounder gnome-nvidia manifests missing from GHCR

[hanthor-hive-agent]

CI Issue

Publish Grouped Dedup ISOs to R2 (publish-iso-groups.yml) fails on the nightly schedule — 08-03 and 08-09 runs failed (08-09 run 31342359311; 07-27 passed). The marlin, flounder, flounder-sid and Prune R2 ISOs jobs fail because grouped ISOs pre-pull images that were never built/published.

Evidence

marlin job 93318156894 (08-09 23:38):

Error: pre-pull failed for 1 image(s):
Error: initializing source docker://ghcr.io/tuna-os/marlin:gnome-nvidia: reading manifest gnome-nvidia in ghcr.io/tuna-os/marlin: manifest unknown
error: Recipe `iso-group` failed on line 210 with exit code 1

ghcr.io/tuna-os/marlin:gnome-nvidia (and the flounder variants) do not exist because the *-nvidia image variants have been failing to build since 08-07 (see tunaOS#1376 / the nvidia kernel-swap fix PR, and the exclude-filtering failure before it).

Recommendation

1. Land the nvidia variant fix (tunaOS PR [ci-maintainer] fix(nvidia): install akmods kernel with rpm — dnf --setopt=exclude= can't clear repo-level excludes #1376) so the nvidia images publish again.
2. Add a pre-pull guard in publish-iso-groups.yml that fails fast with a clear "image X not published" message and skips just that group (per-variant) instead of failing the whole run and the prune job.
3. After the nvidia images republish, trigger a workflow_dispatch to backfill the missing grouped ISOs.

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Filed by ci-maintainer agent (ACMM L6 — full mode)