feat(scenes): add scene darkness reveal and fix project reopen crash

Add darkenScene with Opening brush in presentation, persist reveal strokes per scene during a session, and close projects properly on return to home. Harden dnd asset streaming to avoid Windows main-process crashes when reopening projects.

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

app/main/effects/sceneDarknessStore.test.ts

@@ -0,0 +1,66 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+
+import { SceneDarknessStore } from './sceneDarknessStore';
+
+void test('SceneDarknessStore: сохраняет штрихи при переключении сцен', () => {
+  const store = new SceneDarknessStore();
+  store.switchScene('scene_a', true);
+  store.dispatch({
+    kind: 'stroke.add',
+    stroke: {
+      id: 's1',
+      seed: 1,
+      createdAtMs: 100,
+      points: [{ x: 0.5, y: 0.5, tMs: 100 }],
+      radiusN: 0.08,
+    },
+  });
+
+  store.switchScene('scene_b', true);
+  assert.equal(store.getState().strokes.length, 0);
+
+  store.switchScene('scene_a', true);
+  assert.equal(store.getState().strokes.length, 1);
+  assert.equal(store.getState().strokes[0]?.id, 's1');
+});
+
+void test('SceneDarknessStore: resetSession очищает кэш', () => {
+  const store = new SceneDarknessStore();
+  store.switchScene('scene_a', true);
+  store.dispatch({
+    kind: 'stroke.add',
+    stroke: {
+      id: 's1',
+      seed: 1,
+      createdAtMs: 100,
+      points: [{ x: 0.2, y: 0.2, tMs: 100 }],
+      radiusN: 0.08,
+    },
+  });
+  store.resetSession();
+  store.switchScene('scene_a', true);
+  assert.equal(store.getState().strokes.length, 0);
+});
+
+void test('SceneDarknessStore: draft синхронизируется и сбрасывается при commit', () => {
+  const store = new SceneDarknessStore();
+  store.switchScene('scene_a', true);
+  store.dispatch({
+    kind: 'draft.set',
+    draft: { points: [{ x: 0.1, y: 0.1, tMs: 1 }], radiusN: 0.05 },
+  });
+  assert.ok(store.getState().draft);
+  store.dispatch({
+    kind: 'stroke.add',
+    stroke: {
+      id: 's1',
+      seed: 1,
+      createdAtMs: 100,
+      points: [{ x: 0.1, y: 0.1, tMs: 1 }],
+      radiusN: 0.05,
+    },
+  });
+  assert.equal(store.getState().draft, null);
+  assert.equal(store.getState().strokes.length, 1);
+});

app/main/effects/sceneDarknessStore.ts

@@ -0,0 +1,80 @@
+import type { SceneDarknessEvent, SceneDarknessRevealStroke, SceneDarknessState } from '../../shared/types';
+
+function emptyState(): SceneDarknessState {
+  return {
+    revision: 1,
+    enabled: false,
+    cacheKey: null,
+    strokes: [],
+    draft: null,
+  };
+}
+
+export class SceneDarknessStore {
+  private state: SceneDarknessState = emptyState();
+  /** Кэш раскрытых областей по ключу (graphNodeId или sceneId) на время сессии показа. */
+  private cache = new Map<string, SceneDarknessRevealStroke[]>();
+  private currentKey: string | null = null;
+
+  getState(): SceneDarknessState {
+    return { ...this.state, strokes: [...this.state.strokes] };
+  }
+
+  /** Сброс кэша при новом запуске показа (кнопка «Запустить»). */
+  resetSession(): void {
+    this.cache.clear();
+    this.currentKey = null;
+    this.state = emptyState();
+  }
+
+  /**
+   * Переключение сцены: сохраняем текущие штрихи в кэш и загружаем состояние новой сцены.
+   */
+  switchScene(cacheKey: string | null, enabled: boolean): SceneDarknessState {
+    if (this.currentKey !== null) {
+      this.cache.set(this.currentKey, [...this.state.strokes]);
+    }
+    this.currentKey = cacheKey;
+    const strokes =
+      cacheKey && enabled ? [...(this.cache.get(cacheKey) ?? [])] : [];
+    this.state = {
+      revision: this.state.revision + 1,
+      enabled,
+      cacheKey,
+      strokes,
+      draft: null,
+    };
+    return this.getState();
+  }
+
+  dispatch(event: SceneDarknessEvent): SceneDarknessState {
+    if (!this.state.enabled) return this.getState();
+    switch (event.kind) {
+      case 'draft.set':
+        this.state = {
+          ...this.state,
+          revision: this.state.revision + 1,
+          draft: event.draft,
+        };
+        return this.getState();
+      case 'stroke.add': {
+        const strokes = [...this.state.strokes, event.stroke];
+        if (this.currentKey) {
+          this.cache.set(this.currentKey, strokes);
+        }
+        this.state = {
+          ...this.state,
+          revision: this.state.revision + 1,
+          strokes,
+          draft: null,
+        };
+        return this.getState();
+      }
+      default: {
+        // eslint-disable-next-line @typescript-eslint/no-unused-vars
+        const _x: never = event;
+        return this.getState();
+      }
+    }
+  }
+}