👷 Skip main CI run for release commits

A release pushes main and then a tag pointing at the same commit, so
the branch run re-verifies the identical SHA the tag run already
verifies (and publishes). Add a cheap release-gate job that recognizes
the '🔖 Release x.y.z' commit message on main and skips the
full build/maintain jobs; tag, PR, and ordinary main pushes are
unaffected, and the gate fails open (runs CI) if it errors.

.gitea/workflows/ci.yml

@@ -12,7 +12,42 @@ on:
     workflow_dispatch: {}
 
 jobs:
+    # Cheap gate that collapses the release double-run. `scripts/release.sh`
+    # pushes `main` and the tag seconds apart, and the tag points at exactly
+    # the HEAD commit that push delivers — so the branch run would verify the
+    # identical tree the tag run verifies anyway (plus `publish`). When a push
+    # to `main` is headed by a release commit (`:bookmark: Release x.y.z`, the
+    # single commit release.sh creates), the full CI is skipped here and the
+    # tag run becomes the authoritative one for that SHA. All other pushes —
+    # PRs, tags, ordinary `main` merges — see `skip=false` and run as before.
+    #
+    # Coupling: the pattern below MUST stay in sync with the release commit
+    # message in `scripts/release.sh`. Failure mode if the tag push ever fails
+    # after `main` accepted the release commit: no CI fires; fix by re-running
+    # `git push --tags`.
+    release-gate:
+        runs-on: ubuntu-latest
+        outputs:
+            skip: ${{ steps.decide.outputs.skip }}
+        steps:
+            - uses: actions/checkout@v4
+            - id: decide
+              env:
+                  REF: ${{ gitea.ref }}
+              run: |
+                  # Keyed on the ref, not just the message: a tag run checks out
+                  # the same release commit, and `publish` needs its `build`.
+                  if [ "${REF}" = "refs/heads/main" ] &&
+                      git log -1 --format=%s | grep -qE '^:bookmark: Release [0-9]+\.[0-9]+\.[0-9]+$'; then
+                      echo 'Release commit on main — the tag run covers this SHA; skipping full CI.'
+                      echo 'skip=true' >>"${GITHUB_OUTPUT}"
+                  else
+                      echo 'skip=false' >>"${GITHUB_OUTPUT}"
+                  fi
+
     build:
+        needs: release-gate
+        if: needs.release-gate.outputs.skip != 'true'
         runs-on: ubuntu-latest
         # Bind-mount the shared pages tree so the coverage step below can write
         # into it. The runner whitelists this path via `container.valid_volumes`
@@ -69,6 +104,8 @@ jobs:
     # the Actions tab for visibility, but must never gate a merge — so
     # continue-on-error and intentionally NOT in `publish`'s `needs`.
     maintain:
+        needs: release-gate
+        if: needs.release-gate.outputs.skip != 'true'
         runs-on: ubuntu-latest
         continue-on-error: true
         steps: