feat(service-storage-harness): slice 1 — harness + qbit store + client + integration

ServiceDataHarness (services/service_data.py): lifecycle-only registry of
per-concern storage — DB provisioning, idempotent migrations (ALTER TABLE
duplicate-column-name caught per-statement), cascade_delete(service_id).
QbittorrentSampleStore: append/window/prune (MAX_SAMPLES=120) in
qbittorrent.db. QbittorrentClient: cookie-login Web API client (403 re-login,
/sync/maindata). Integration registered with 3 widget kinds (totals/active/
speed). Harness initialized in main.py lifespan.

Backend: 314 pytest pass (21 new), ruff clean.

backend/tests/test_qbittorrent_client.py

@@ -0,0 +1,134 @@
+"""Unit tests for the QbittorrentClient."""
+
+from __future__ import annotations
+
+import unittest
+from unittest.mock import MagicMock, patch
+
+import requests
+
+from media_library_viewer_api.clients.qbittorrent import QbittorrentClient
+
+
+class QbittorrentClientTests(unittest.TestCase):
+    def setUp(self) -> None:
+        self.client = QbittorrentClient("https://qb.example.com", "admin", "secret", timeout=5)
+        self.session = MagicMock()
+        self.client._session = self.session
+
+    def _login_response(self, text: str = "Ok.") -> MagicMock:
+        resp = MagicMock()
+        resp.text = text
+        resp.raise_for_status.return_value = None
+        resp.status_code = 200
+        return resp
+
+    def _get_response(self, json_data: dict, status_code: int = 200) -> MagicMock:
+        resp = MagicMock()
+        resp.json.return_value = json_data
+        resp.raise_for_status.return_value = None
+        resp.status_code = status_code
+        resp.text = ""
+        return resp
+
+    def test_base_url_appends_api_v2(self) -> None:
+        c = QbittorrentClient("https://qb.example.com", "u", "p")
+        self.assertEqual(c.base_url, "https://qb.example.com/api/v2")
+
+    def test_base_url_keeps_existing_api_v2(self) -> None:
+        c = QbittorrentClient("https://qb.example.com/api/v2", "u", "p")
+        self.assertEqual(c.base_url, "https://qb.example.com/api/v2")
+
+    def test_base_url_strips_trailing_slash(self) -> None:
+        c = QbittorrentClient("https://qb.example.com/", "u", "p")
+        self.assertEqual(c.base_url, "https://qb.example.com/api/v2")
+
+    def test_empty_base_url_raises(self) -> None:
+        with self.assertRaises(ValueError):
+            QbittorrentClient("", "u", "p")
+
+    def test_empty_username_raises(self) -> None:
+        with self.assertRaises(ValueError):
+            QbittorrentClient("https://qb.example.com", "", "p")
+
+    def test_login_posts_credentials(self) -> None:
+        self.session.post.return_value = self._login_response("Ok.")
+        self.client._login()
+        self.session.post.assert_called_once()
+        call_args = self.session.post.call_args
+        self.assertIn("/auth/login", call_args.args[0])
+        self.assertEqual(call_args.kwargs["data"], {"username": "admin", "password": "secret"})
+        self.assertTrue(self.client._logged_in)
+
+    def test_login_failure_raises_runtime_error(self) -> None:
+        self.session.post.return_value = self._login_response("Fails.")
+        with self.assertRaises(RuntimeError):
+            self.client._login()
+
+    def test_get_auto_logs_in_on_first_call(self) -> None:
+        """First _get triggers login, then fetches data."""
+        self.session.post.return_value = self._login_response("Ok.")
+        self.session.get.return_value = self._get_response({"server_state": {}, "torrents": {}})
+
+        result = self.client._get("/sync/maindata")
+
+        self.session.post.assert_called_once()  # login happened
+        self.assertEqual(result, {"server_state": {}, "torrents": {}})
+
+    def test_cookie_reuse_does_not_re_login(self) -> None:
+        """After login, subsequent _get calls do NOT re-login."""
+        self.client._logged_in = True  # simulate already logged in
+        self.session.get.return_value = self._get_response({"data": 1})
+
+        self.client._get("/some/path")
+
+        self.session.post.assert_not_called()  # no re-login
+
+    def test_403_triggers_re_login(self) -> None:
+        """A 403 response triggers re-login and retries the GET."""
+        self.client._logged_in = True  # already logged in from a prior call
+        forbidden = MagicMock()
+        forbidden.status_code = 403
+        ok = self._get_response({"server_state": {}, "torrents": {}})
+        self.session.get.side_effect = [forbidden, ok]
+        self.session.post.return_value = self._login_response("Ok.")
+
+        result = self.client._get("/sync/maindata")
+
+        self.assertEqual(self.session.get.call_count, 2)  # initial + retry
+        self.session.post.assert_called_once()  # re-login happened
+        self.assertEqual(result, {"server_state": {}, "torrents": {}})
+
+    def test_maindata_returns_full_payload(self) -> None:
+        self.client._logged_in = True
+        payload = {
+            "server_state": {"dl_info_speed": 12345, "up_info_speed": 6789},
+            "torrents": {
+                "abc": {"name": "Movie.mkv", "state": "downloading", "progress": 0.5},
+                "def": {"name": "Show.mkv", "state": "uploading", "progress": 1.0},
+            },
+        }
+        self.session.get.return_value = self._get_response(payload)
+
+        result = self.client.maindata()
+
+        self.assertEqual(result["server_state"]["dl_info_speed"], 12345)
+        self.assertEqual(len(result["torrents"]), 2)
+
+    @patch("media_library_viewer_api.clients.qbittorrent.requests.Session")
+    def test_login_http_error_propagates(self, mock_session_cls: MagicMock) -> None:
+        """A network error during login propagates as requests exception."""
+        mock_session = MagicMock()
+        mock_session_cls.return_value = mock_session
+        bad_resp = MagicMock()
+        bad_resp.raise_for_status.side_effect = requests.ConnectionError("refused")
+        bad_resp.text = ""
+        mock_session.post.return_value = bad_resp
+
+        client = QbittorrentClient("https://qb.example.com", "u", "p")
+        with self.assertRaises(requests.ConnectionError):
+            client._login()
+
+
+if __name__ == "__main__":
+    unittest.main()