Document yarn cache behavior in CI

Author: ibgreen

.github/workflows/test.yaml

@@ -30,6 +30,7 @@ jobs:
 
       # ✅ Cache Yarn 4's compressed archives
       - name: Cache Yarn 4 artifacts
+        id: yarn-cache
         uses: actions/cache@v4
         with:
           path: |
@@ -47,6 +48,7 @@ jobs:
           node -p "process.versions"
 
       - name: Install deps
+        # Always run to materialize node_modules; the cache only restores tarballs.
         run: yarn --frozen-lockfile
 
       # Sanity-check that Vite sees the root config (this MUST be true)