feat(effects): add Closing brush as inverse of Opening brush

Allow covering revealed darkness again during darkened scene sessions.

Co-authored-by: Cursor <cursoragent@cursor.com>

app/main/effects/sceneDarknessStore.test.ts

@@ -48,9 +48,10 @@ void test('SceneDarknessStore: draft синхронизируется и сбр
   store.switchScene('scene_a', true);
   store.dispatch({
     kind: 'draft.set',
-    draft: { points: [{ x: 0.1, y: 0.1, tMs: 1 }], radiusN: 0.05 },
+    draft: { points: [{ x: 0.1, y: 0.1, tMs: 1 }], radiusN: 0.05, mode: 'cover' },
   });
   assert.ok(store.getState().draft);
+  assert.equal(store.getState().draft?.mode, 'cover');
   store.dispatch({
     kind: 'stroke.add',
     stroke: {
@@ -59,8 +60,42 @@ void test('SceneDarknessStore: draft синхронизируется и сбр
       createdAtMs: 100,
       points: [{ x: 0.1, y: 0.1, tMs: 1 }],
       radiusN: 0.05,
+      mode: 'cover',
     },
   });
   assert.equal(store.getState().draft, null);
   assert.equal(store.getState().strokes.length, 1);
 });
+
+void test('SceneDarknessStore: cover-штрих сохраняется в кэше сцены', () => {
+  const store = new SceneDarknessStore();
+  store.switchScene('scene_a', true);
+  store.dispatch({
+    kind: 'stroke.add',
+    stroke: {
+      id: 'open1',
+      seed: 1,
+      createdAtMs: 100,
+      points: [{ x: 0.5, y: 0.5, tMs: 100 }],
+      radiusN: 0.08,
+      mode: 'reveal',
+    },
+  });
+  store.dispatch({
+    kind: 'stroke.add',
+    stroke: {
+      id: 'close1',
+      seed: 2,
+      createdAtMs: 200,
+      points: [{ x: 0.5, y: 0.5, tMs: 200 }],
+      radiusN: 0.08,
+      mode: 'cover',
+    },
+  });
+  assert.equal(store.getState().strokes.length, 2);
+  assert.equal(store.getState().strokes[1]?.mode, 'cover');
+  store.switchScene('scene_b', true);
+  store.switchScene('scene_a', true);
+  assert.equal(store.getState().strokes.length, 2);
+  assert.equal(store.getState().strokes[1]?.mode, 'cover');
+});