fix: API 입력 이벤트의 원자적 재실행을 보장한다

app/game-api/test/requestId.test.ts

@@ -1,6 +1,7 @@
 import { describe, expect, it } from 'vitest';
 
 import { scopeHttpIdempotencyKey } from '../src/requestId.js';
+import { scopeApiInputEventRequestId } from '../src/trpc.js';
 
 describe('HTTP idempotency request IDs', () => {
     it('is stable for one principal and isolated across users and profiles', () => {
@@ -24,4 +25,12 @@ describe('HTTP idempotency request IDs', () => {
         expect(scoped).toMatch(/^http:[0-9a-f]{64}$/u);
         expect(scoped).toHaveLength(69);
     });
+
+    it('keeps the first call compatible and isolates later calls in a same-path batch', () => {
+        expect(scopeApiInputEventRequestId('http:base', 'messages.send', 0)).toBe('http:base:messages.send');
+        expect(scopeApiInputEventRequestId('http:base', 'messages.send', 1)).toBe('http:base:messages.send:batch:1');
+        expect(scopeApiInputEventRequestId('http:base', 'messages.send', 2)).not.toBe(
+            scopeApiInputEventRequestId('http:base', 'messages.send', 1)
+        );
+    });
 });