test: добавить Stage 6 в golden-матрицу (#673)

Issue: #673
User-Visible: no

scripts/mutation-registry.mjs

@@ -10792,6 +10792,16 @@ const MUTANT_DEFINITIONS = [
       replace: '  rotDeg: 4,\n',
     }],
   },
+  {
+    id: 'stage6-acceptance-left-diagnostic-only',
+    guard: 'node --test --test-name-pattern="#673" test/golden-matrix.test.mjs',
+    because: '#673: the five approved Stage 6 frames must be in the canonical matrix, not only the diagnostic exporter',
+    patches: [{
+      file: 'demo/golden/matrix.mjs',
+      find: '  ...STAGE6_ACCEPTANCE_SCENARIOS,\n  // #663 AC3/AC10/AC12:',
+      replace: '  // mutant: Stage 6 acceptance remains diagnostic-only\n  // #663 AC3/AC10/AC12:',
+    }],
+  },
   {
     id: 'stage3-w2-room-label-left-on-floor',
     guard: 'node --test --test-name-pattern="exact Stage 4 overlay matrix" test/iso-overlays.test.mjs',