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_service_data.py

@@ -0,0 +1,148 @@
+"""Tests for ServiceDataHarness lifecycle and QbittorrentSampleStore operations."""
+
+from __future__ import annotations
+
+import pytest
+
+from media_library_viewer_api.services.qbittorrent_store import (
+    MAX_SAMPLES,
+    QBITTORRENT_CONCERN,
+    QbittorrentSampleStore,
+)
+from media_library_viewer_api.services.service_data import (
+    ServiceDataHarness,
+    StorageConcern,
+)
+
+# A throwaway concern used to test harness lifecycle in isolation.
+_TEST_CONCERN = StorageConcern(
+    concern_key="test",
+    db_filename="test.db",
+    migrations=[
+        """
+        CREATE TABLE IF NOT EXISTS test_items (
+            id INTEGER PRIMARY KEY,
+            service_id TEXT NOT NULL,
+            value TEXT
+        );
+        CREATE INDEX IF NOT EXISTS idx_test_service ON test_items(service_id);
+        """
+    ],
+    tables=["test_items"],
+)
+
+
+class TestServiceDataHarnessMigrations:
+    def test_run_migrations_creates_tables(self, tmp_path):
+        harness = ServiceDataHarness(tmp_path)
+        harness.register(_TEST_CONCERN)
+        harness.run_migrations()
+
+        with harness.connect("test") as conn:
+            tables = {row[0] for row in conn.execute("SELECT name FROM sqlite_master WHERE type='table'").fetchall()}
+        assert "test_items" in tables
+
+    def test_migrations_are_idempotent(self, tmp_path):
+        """Re-running migrations on an already-migrated DB must not crash."""
+        harness = ServiceDataHarness(tmp_path)
+        harness.register(_TEST_CONCERN)
+        harness.run_migrations()
+        harness.run_migrations()  # should not raise
+
+    def test_alter_table_idempotency(self, tmp_path):
+        """ALTER TABLE ADD COLUMN must be silently skipped on re-run."""
+        concern = StorageConcern(
+            concern_key="alter_test",
+            db_filename="alter.db",
+            migrations=[
+                "CREATE TABLE IF NOT EXISTS items (id INTEGER PRIMARY KEY)",
+                "ALTER TABLE items ADD COLUMN extra TEXT DEFAULT ''",
+            ],
+            tables=["items"],
+        )
+        harness = ServiceDataHarness(tmp_path)
+        harness.register(concern)
+        harness.run_migrations()
+        harness.run_migrations()  # second run: "duplicate column name" caught
+
+        with harness.connect("alter_test") as conn:
+            cols = {row[1] for row in conn.execute("PRAGMA table_info(items)").fetchall()}
+        assert "extra" in cols
+
+
+class TestServiceDataHarnessCascadeDelete:
+    def test_cascade_delete_removes_only_matching_service(self, tmp_path):
+        harness = ServiceDataHarness(tmp_path)
+        harness.register(_TEST_CONCERN)
+        harness.run_migrations()
+
+        with harness.connect("test") as conn:
+            conn.execute("INSERT INTO test_items (id, service_id, value) VALUES (1, 'svc-a', 'a1')")
+            conn.execute("INSERT INTO test_items (id, service_id, value) VALUES (2, 'svc-a', 'a2')")
+            conn.execute("INSERT INTO test_items (id, service_id, value) VALUES (3, 'svc-b', 'b1')")
+            conn.commit()
+
+        harness.cascade_delete("svc-a")
+
+        with harness.connect("test") as conn:
+            remaining = conn.execute("SELECT service_id, value FROM test_items ORDER BY id").fetchall()
+        assert len(remaining) == 1
+        assert remaining[0][0] == "svc-b"
+
+    def test_cascade_delete_skips_missing_concern_db(self, tmp_path):
+        """cascade_delete on a concern whose DB file doesn't exist should not crash."""
+        harness = ServiceDataHarness(tmp_path)
+        harness.register(_TEST_CONCERN)
+        # No run_migrations → DB file doesn't exist
+        harness.cascade_delete("svc-x")  # should not raise
+
+
+class TestQbittorrentSampleStore:
+    @pytest.fixture()
+    def store(self, tmp_path):
+        harness = ServiceDataHarness(tmp_path)
+        harness.register(QBITTORRENT_CONCERN)
+        harness.run_migrations()
+        return QbittorrentSampleStore(harness=harness)
+
+    def test_append_and_window(self, store):
+        store.append("svc-1", ts=100, dl_speed=500, up_speed=50)
+        store.append("svc-1", ts=200, dl_speed=600, up_speed=60)
+        store.append("svc-1", ts=300, dl_speed=700, up_speed=70)
+
+        samples = store.window("svc-1")
+        assert len(samples) == 3
+        assert samples[0]["ts"] == 100
+        assert samples[2]["ts"] == 300
+        assert samples[1]["dl_speed"] == 600
+
+    def test_window_with_since_ts(self, store):
+        store.append("svc-1", ts=100, dl_speed=500, up_speed=50)
+        store.append("svc-1", ts=200, dl_speed=600, up_speed=60)
+        store.append("svc-1", ts=300, dl_speed=700, up_speed=70)
+
+        samples = store.window("svc-1", since_ts=200)
+        assert len(samples) == 2
+        assert samples[0]["ts"] == 200
+
+    def test_prune_enforces_max_samples(self, store):
+        for i in range(MAX_SAMPLES + 10):
+            store.append("svc-1", ts=i, dl_speed=i, up_speed=i)
+
+        samples = store.window("svc-1")
+        assert len(samples) == MAX_SAMPLES
+        # The oldest 10 should have been pruned
+        assert samples[0]["ts"] == 10
+        assert samples[-1]["ts"] == MAX_SAMPLES + 9
+
+    def test_two_services_do_not_cross_contaminate(self, store):
+        store.append("svc-a", ts=100, dl_speed=500, up_speed=50)
+        store.append("svc-b", ts=200, dl_speed=600, up_speed=60)
+
+        a_samples = store.window("svc-a")
+        b_samples = store.window("svc-b")
+
+        assert len(a_samples) == 1
+        assert a_samples[0]["dl_speed"] == 500
+        assert len(b_samples) == 1
+        assert b_samples[0]["dl_speed"] == 600