feat(engine): execute story actions via storyChoiceId

src/engine/__tests__/storyActions.test.ts

@@ -0,0 +1,22 @@
+import { describe, expect, it } from 'vitest';
+import { content } from '../../content/index';
+import { createGameState, executeStoryAction } from '../game';
+import { enterStoryNode } from '../story';
+
+describe('executeStoryAction()', () => {
+  it('applies the linked story choice', () => {
+    const state = createGameState(content);
+    enterStoryNode(state, content, 'fork_choice');
+    executeStoryAction(state, content, 'pick_high_road');
+    expect(state.storyFlags.route_a).toBe(true);
+    expect(state.currentStoryNodeId).toBe('route_a_beat');
+  });
+
+  it('throws when the choice is not available', () => {
+    const state = createGameState(content);
+    enterStoryNode(state, content, 'fork_choice');
+    executeStoryAction(state, content, 'pick_high_road');
+    // after taking route A, the current node has no choices, so follow_river (pick_b) is unavailable
+    expect(() => executeStoryAction(state, content, 'follow_river')).toThrow();
+  });
+});