feat(packs-lab): DSM 호출 retry/backoff + 업로드 cleanup 보강

- dsm_client.py: _request_with_retry()로 5xx·transport·timeout만 지수백오프
  재시도 (DSM_MAX_RETRIES, DSM_BACKOFF_SEC env). DSM error code 응답 본문 로깅.
- routes.py: upload 핸들러를 try/finally로 감싸 부분파일 정리 보장, Supabase
  INSERT 호출 자체에 try/except 추가해 네트워크 예외도 cleanup.
- test_dsm_client.py: retry 시나리오 4종 추가 (5xx→성공/소진/transport
  error/4xx no-retry). 전체 29 테스트 pass.

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

packs-lab/tests/test_dsm_client.py

@@ -8,6 +8,13 @@ import httpx
 from app.dsm_client import create_share_link, DSMError
 
 
+@pytest.fixture(autouse=True)
+def _no_backoff(monkeypatch):
+    """retry 백오프 sleep 제거 — 테스트 속도."""
+    from app import dsm_client
+    monkeypatch.setattr(dsm_client, "DSM_BACKOFF_SEC", 0.0)
+
+
 @pytest.fixture(autouse=True)
 def _dsm_env(monkeypatch):
     monkeypatch.setenv("DSM_HOST", "https://test-nas:5001")
@@ -109,3 +116,109 @@ def test_dsm_share_failure_logs_out():
 
     assert "login" in call_order
     assert "logout" in call_order, "logout이 호출되지 않음 (finally 누락 의심)"
+
+
+def test_retry_on_5xx_then_success(monkeypatch):
+    """첫 호출 5xx → retry → 두 번째 200으로 성공."""
+    from app import dsm_client
+    monkeypatch.setattr(dsm_client, "DSM_MAX_RETRIES", 3)
+
+    login_calls = {"n": 0}
+
+    async def fake_get(self, url, *, params=None, **kw):
+        method = (params or {}).get("method", "")
+        if method == "login":
+            login_calls["n"] += 1
+            if login_calls["n"] == 1:
+                return _make_response({}, status_code=503)
+            return _make_response({"success": True, "data": {"sid": "sid-after-retry"}})
+        if method == "create":
+            return _make_response({
+                "success": True,
+                "data": {"links": [{"url": "https://nas/sharing/retry"}]},
+            })
+        return _make_response({"success": True})
+
+    with patch.object(httpx.AsyncClient, "get", new=fake_get):
+        url, _ = asyncio.run(create_share_link("/volume1/x.zip"))
+
+    assert url == "https://nas/sharing/retry"
+    assert login_calls["n"] == 2, "5xx 응답에 대해 retry가 동작해야 함"
+
+
+def test_retry_exhausts_on_persistent_5xx(monkeypatch):
+    """5xx가 MAX_RETRIES 동안 계속되면 DSMError로 raise."""
+    from app import dsm_client
+    monkeypatch.setattr(dsm_client, "DSM_MAX_RETRIES", 2)
+
+    login_calls = {"n": 0}
+
+    async def fake_get(self, url, *, params=None, **kw):
+        method = (params or {}).get("method", "")
+        if method == "login":
+            login_calls["n"] += 1
+            return _make_response({}, status_code=503)
+        return _make_response({"success": True})
+
+    with patch.object(httpx.AsyncClient, "get", new=fake_get):
+        with pytest.raises(DSMError, match="재시도"):
+            asyncio.run(create_share_link("/volume1/x.zip"))
+
+    assert login_calls["n"] == 2, f"MAX_RETRIES만큼 시도해야 함 (실제: {login_calls['n']})"
+
+
+def test_retry_on_transport_error_then_success(monkeypatch):
+    """httpx.ConnectError → retry → 성공."""
+    from app import dsm_client
+    monkeypatch.setattr(dsm_client, "DSM_MAX_RETRIES", 3)
+
+    login_calls = {"n": 0}
+
+    async def fake_get(self, url, *, params=None, **kw):
+        method = (params or {}).get("method", "")
+        if method == "login":
+            login_calls["n"] += 1
+            if login_calls["n"] == 1:
+                raise httpx.ConnectError("connection refused")
+            return _make_response({"success": True, "data": {"sid": "sid"}})
+        if method == "create":
+            return _make_response({
+                "success": True,
+                "data": {"links": [{"url": "https://nas/sharing/tr"}]},
+            })
+        return _make_response({"success": True})
+
+    with patch.object(httpx.AsyncClient, "get", new=fake_get):
+        url, _ = asyncio.run(create_share_link("/volume1/x.zip"))
+
+    assert url == "https://nas/sharing/tr"
+    assert login_calls["n"] == 2
+
+
+def test_no_retry_on_4xx(monkeypatch):
+    """4xx (영구 오류)는 retry 없이 즉시 raise_for_status."""
+    from app import dsm_client
+    monkeypatch.setattr(dsm_client, "DSM_MAX_RETRIES", 3)
+
+    login_calls = {"n": 0}
+
+    def _raise_4xx():
+        raise httpx.HTTPStatusError(
+            "client error",
+            request=MagicMock(),
+            response=MagicMock(status_code=403),
+        )
+
+    async def fake_get(self, url, *, params=None, **kw):
+        login_calls["n"] += 1
+        resp = MagicMock(spec=httpx.Response)
+        resp.status_code = 403
+        resp.json.return_value = {}
+        resp.raise_for_status = _raise_4xx
+        return resp
+
+    with patch.object(httpx.AsyncClient, "get", new=fake_get):
+        with pytest.raises(httpx.HTTPStatusError):
+            asyncio.run(create_share_link("/volume1/x.zip"))
+
+    assert login_calls["n"] == 1, "4xx는 retry 없이 즉시 raise"