Nightly #25 built all platform artifacts successfully (ccache-free), but the Publish nightly pre-release job failed.

Root cause

The Create signed nightly tag step does:

git tag -s "$TAG" ... HEAD          # local signed tag OBJECT
TAG_SHA=$(git rev-parse "$TAG")     # SHA of that local object
gh api .../git/refs -f sha="$TAG_SHA"  # 422 Object does not exist

The git/refs API can only point a ref at a SHA that already exists on the server. The local signed tag object was never uploaded → HTTP 422 'Object does not exist'.

Affects the 2.7.1 release too (same code).

Fix

Push the signed tag directly (preserves signature; a tag push adds no commits so workflow push-protection doesn't apply), with a correct two-step API fallback.