♻️ Assert the baked tool cache instead of logging it

The diagnostics did their job (missing <version>/<arch>.complete marker, now
written by the image). Replace the noise with a fail-fast assert that names
the same invariant, mirroring the publish job's NPM_TOKEN check: a stale tag
on the runner would otherwise silently reintroduce the per-job download, with
nothing in the repo to catch it.

.gitea/workflows/ci.yml

@@ -63,24 +63,13 @@ jobs:
                 - /data/gitea-pages:/data/gitea-pages
         steps:
             - uses: actions/checkout@v4
-            # TEMPORARY (remove once understood): the image provably carries
-            # the tool-cache entry (verified with `docker run --rm <image> ls
-            # /opt/hostedtoolcache/node/26.8.2/x64/bin`), yet setup-node still
-            # downloads. Print what the job container actually sees at
-            # runtime, mounts first — a mount over /opt/hostedtoolcache would
-            # hide the baked directory from the probe.
-            - name: Tool cache diagnostics
+            # Fail fast when the job container is not the baked image: a stale
+            # tag on the runner (`forcePull=false` in its pull log) silently
+            # reintroduces the per-job download. Mirrors the publish job's
+            # NPM_TOKEN assert — cheap, and it names the invariant.
+            - name: Assert the baked tool cache is present
               run: |
-                  id
-                  grep -E 'hostedtoolcache|workspace|overlay' /proc/mounts || true
-                  ls -la /opt/hostedtoolcache || true
-                  ls -la /opt/hostedtoolcache/node || true
-                  ls -la "/opt/hostedtoolcache/node/$(tr -d '[:space:]' < .node-version)/" || true
-                  test -f "/opt/hostedtoolcache/node/$(tr -d '[:space:]' < .node-version)/x64.complete" && echo MARKER-PRESENT || echo MARKER-MISSING
-                  ls -la "/opt/hostedtoolcache/node/$(tr -d '[:space:]' < .node-version)/x64/bin" || true
-                  "/opt/hostedtoolcache/node/$(tr -d '[:space:]' < .node-version)/x64/bin/node" -v || true
-                  env | grep -iE 'RUNNER|TOOL|CACHE' || true
-                  head -2 /etc/os-release
+                  test -f "/opt/hostedtoolcache/node/$(tr -d '[:space:]' < .node-version)/x64.complete"
             - uses: actions/setup-node@v4
               with:
                   node-version-file: .node-version