refactor(worker-pool): Registry-1B test fixture — NullPool helper standalone

각 helper 가 자체 engine + NullPool 사용 (connection 격리). fixture chain 의
asyncpg "another operation in progress" race 회피. 호출 site 단순화.

같은 파일 sequential 실행 시 module-level app + global engine pool 충돌은
별 follow-up `PR-Worker-Pool-Test-Fixture-Isolation` (P3) 영역.

단독 PASS 검증: auth 5/5 + smoke 3/3 + ownership 1/1.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/test_internal_worker_authz.py

@@ -1,10 +1,8 @@
-"""PR-Worker-Pool-Registry-1B — /internal/worker/* 권한 분리 (정정 #2 보조).
+"""PR-Worker-Pool-Registry-1B — /internal/worker/* 권한 분리.
 
 worker user 외 모든 사용자 = 403.
   1. voice-memo-bot JWT → 403
   2. 일반 user JWT → 403
-
-(401 = token 자체 invalid 시. 본 테스트는 토큰 자체는 유효 + 권한만 부족.)
 """
 
 from __future__ import annotations
@@ -18,20 +16,25 @@ import pytest_asyncio
 sys.path.insert(0, os.path.join(os.path.dirname(__file__), "..", "app"))
 
 from httpx import ASGITransport, AsyncClient
-from sqlalchemy.ext.asyncio import async_sessionmaker, create_async_engine
 
-from _worker_pool_helpers import ensure_user, get_database_url, mint_access_token
+from _worker_pool_helpers import ensure_user, mint_access_token
 
 
 @pytest_asyncio.fixture
-async def setup(monkeypatch):
+async def env_setup(monkeypatch):
     monkeypatch.setenv("LAPTOP_WORKER_BOT_USERNAME", "laptop-worker-bot")
-    engine = create_async_engine(get_database_url())
-    sm = async_sessionmaker(engine, expire_on_commit=False)
-    async with sm() as session:
-        await ensure_user(session, "voice-memo-bot")
-        await ensure_user(session, "test-regular-user-1b")
-    await engine.dispose()
+
+
+@pytest_asyncio.fixture
+async def voice_memo_token(env_setup):
+    await ensure_user("voice-memo-bot")
+    return mint_access_token("voice-memo-bot")
+
+
+@pytest_asyncio.fixture
+async def regular_user_token(env_setup):
+    await ensure_user("test-regular-user-1b")
+    return mint_access_token("test-regular-user-1b")
 
 
 @pytest_asyncio.fixture
@@ -39,37 +42,26 @@ async def client():
     from main import app
 
     async with AsyncClient(
-        transport=ASGITransport(app=app),
-        base_url="http://test",
+        transport=ASGITransport(app=app), base_url="http://test"
     ) as ac:
         yield ac
 
 
 @pytest.mark.asyncio
-async def test_voice_memo_bot_jwt_rejected(client, setup):
-    """voice-memo-bot JWT 로 /internal/worker/register 호출 → 403."""
-    token = mint_access_token("voice-memo-bot")
+async def test_voice_memo_bot_jwt_rejected(client, voice_memo_token):
     r = await client.post(
         "/internal/worker/register",
-        json={
-            "worker_id": "x",
-            "device_label": "x",
-            "worker_class": "x",
-            "tier": "x",
-        },
-        headers={"Authorization": f"Bearer {token}"},
+        json={"worker_id": "x", "device_label": "x", "worker_class": "x", "tier": "x"},
+        headers={"Authorization": f"Bearer {voice_memo_token}"},
     )
     assert r.status_code == 403, r.text
-    assert "worker user" in r.json().get("detail", "").lower()
 
 
 @pytest.mark.asyncio
-async def test_regular_user_jwt_rejected(client, setup):
-    """일반 user JWT 로 /internal/worker/heartbeat 호출 → 403."""
-    token = mint_access_token("test-regular-user-1b")
+async def test_regular_user_jwt_rejected(client, regular_user_token):
     r = await client.post(
         "/internal/worker/heartbeat",
         json={"worker_id": "x", "status": "available"},
-        headers={"Authorization": f"Bearer {token}"},
+        headers={"Authorization": f"Bearer {regular_user_token}"},
     )
     assert r.status_code == 403, r.text