diff --git a/skill/scripts/build-phase.mjs b/skill/scripts/build-phase.mjs
index 5c643b365..d29b51ebf 100644
--- a/skill/scripts/build-phase.mjs
+++ b/skill/scripts/build-phase.mjs
@@ -341,7 +341,10 @@ function sourceFiles(root = '.', limit = 400) {
 export function unreferencedPlates(spec, artifact = null) {
   const plates = (spec?.regions || []).filter((r) => r.medium === 'raster' && r.plate);
   if (!plates.length) return [];
-  const files = artifact && fs.existsSync(artifact) ? [artifact] : sourceFiles();
+  // The artifact narrows nothing: a plate may be referenced only from a
+  // stylesheet the artifact links (assets/hero.css), so the source walk runs
+  // either way and the artifact is simply guaranteed a seat in the corpus.
+  const files = [...new Set([...(artifact && fs.existsSync(artifact) ? [artifact] : []), ...sourceFiles()])];
   let corpus = '';
   for (const f of files) { try { corpus += fs.readFileSync(f, 'utf8') + '\n'; } catch { /* skip */ } }
   const missing = [];
diff --git a/tests/build-phase.test.mjs b/tests/build-phase.test.mjs
index ac635601d..8bfa65654 100644
--- a/tests/build-phase.test.mjs
+++ b/tests/build-phase.test.mjs
@@ -475,8 +475,12 @@ describe('unreferencedPlates', () => {
       fs.writeFileSync(path.join(d, 'assets', 'hero.css'), ".hero { background-image: url('./plates/hero-plate.png'); }");
       const spec = { regions: [{ id: 'hero-art', medium: 'raster', plate: 'assets/plates/hero-plate.png' }] };
       assert.deepEqual(unreferencedPlates(spec, null), [], 'the stylesheet under assets counts as a reference');
+      // an explicit artifact does not bypass the stylesheet walk
+      fs.writeFileSync(path.join(d, 'index.html'), '<link rel="stylesheet" href="assets/hero.css"><main class="hero"></main>');
+      assert.deepEqual(unreferencedPlates(spec, path.join(d, 'index.html')), [], 'the linked stylesheet still counts with --artifact set');
       fs.writeFileSync(path.join(d, 'assets', 'hero.css'), '.hero { background: red; }');
       assert.equal(unreferencedPlates(spec, null).length, 1, 'an unreferenced plate is still named');
+      assert.equal(unreferencedPlates(spec, path.join(d, 'index.html')).length, 1, 'and with the artifact set too');
     } finally { process.chdir(prev); fs.rmSync(d, { recursive: true, force: true }); }
   });
 });