feat: port NPC possession through turn daemon

app/game-engine/test/npcPossessionService.test.ts

@@ -0,0 +1,11 @@
+import { describe, expect, it } from 'vitest';
+
+import { buildNpcSelectionTokenSeed } from '../src/turn/npcPossessionService.js';
+
+describe('NPC possession legacy token contracts', () => {
+    it('builds the Ref SelectNPCToken seed from the Seoul whole-second timestamp', () => {
+        expect(buildNpcSelectionTokenSeed('seed', 42, new Date('2026-07-30T23:59:58.987Z'))).toBe(
+            'str(4,seed)|str(14,SelectNPCToken)|int(42)|str(19,2026-07-31 08:59:58)'
+        );
+    });
+});