feat(service-storage-harness): slice 4 — cascade-delete wiring + integration test

Wire ServiceDataHarness.cascade_delete into SettingsStore.delete_service
(best-effort try/except, logs on failure). Fix migration runner to also
catch 'no such table' on fresh DBs (ALTER TABLE before init_schema).
Integration test proves end-to-end cascade across both concerns (qBit
samples + media items) with multi-instance preservation.

Backend: 322 pytest pass, ruff clean.

backend/src/media_library_viewer_api/services/service_data.py

@@ -95,8 +95,9 @@ class ServiceDataHarness:
                         try:
                             conn.execute(stmt)
                         except sqlite3.OperationalError as exc:
-                            if "duplicate column name" in str(exc).lower():
+                            lowered = str(exc).lower()
-                                logger.debug("Skipping already-applied migration: %s", stmt[:80])
+                            if "duplicate column name" in lowered or "no such table" in lowered:
+                                logger.debug("Skipping migration (already applied or table absent): %s", stmt[:80])
                             else:
                                 raise
                 conn.commit()

backend/src/media_library_viewer_api/services/settings_store.py

@@ -1740,7 +1740,7 @@ class SettingsStore:
         return self.get_service(service["id"]) or service
 
     def delete_service(self, service_id: str) -> None:
-        """Delete a service and cascade-delete widgets referencing it."""
+        """Delete a service and cascade-delete widgets + harness data."""
         self.init_schema()
         with self.connect() as conn:
             # The service_id column on dashboard_widgets is added in a later
@@ -1753,6 +1753,15 @@ class SettingsStore:
                 )
             conn.execute("DELETE FROM services WHERE id = ?", (service_id,))
 
+        # Cascade-delete harness-managed data (best-effort: the service row is
+        # already removed; data cleanup must not block service deletion).
+        try:
+            from media_library_viewer_api.services.service_data import get_service_data_harness
+
+            get_service_data_harness().cascade_delete(service_id)
+        except Exception:
+            logger.exception("Failed to cascade-delete harness data for service %s", service_id)
+
     def record_service_task_run(self, payload: dict[str, Any]) -> dict[str, Any]:
         """Append a service task run history row."""
         self.init_schema()

backend/tests/test_media_index.py

@@ -228,16 +228,20 @@ class TestMediaIndexQuery:
 
 class TestMediaIndexReplace:
     def test_replace_clears_old(self, index):
-        index.replace_items([
+        index.replace_items(
-            {"id": "x", "title": "Old", "type": "Movie", "library_id": "l1", "library_name": "L1"},
+            [
-        ])
+                {"id": "x", "title": "Old", "type": "Movie", "library_id": "l1", "library_name": "L1"},
+            ]
+        )
         status = index.status()
         assert status.item_count == 1
 
-        index.replace_items([
+        index.replace_items(
-            {"id": "y", "title": "New1", "type": "Movie", "library_id": "l1", "library_name": "L1"},
+            [
-            {"id": "z", "title": "New2", "type": "Movie", "library_id": "l1", "library_name": "L1"},
+                {"id": "y", "title": "New1", "type": "Movie", "library_id": "l1", "library_name": "L1"},
-        ])
+                {"id": "z", "title": "New2", "type": "Movie", "library_id": "l1", "library_name": "L1"},
+            ]
+        )
         status = index.status()
         assert status.item_count == 2
 
@@ -335,15 +339,11 @@ class TestMediaIndexBuildPaths:
                 self.calls.append(kwargs.get("start_index", 0))
                 if kwargs.get("start_index", 0) == 0:
                     return {
-                        "Items": [
+                        "Items": [{"Id": "m1", "Name": "Movie One", "Type": "Movie", "Path": "/media/a.mkv"}],
-                            {"Id": "m1", "Name": "Movie One", "Type": "Movie", "Path": "/media/a.mkv"}
-                        ],
                         "TotalRecordCount": 2,
                     }
                 return {
-                    "Items": [
+                    "Items": [{"Id": "m2", "Name": "Movie Two", "Type": "Movie", "Path": "/media/b.mkv"}],
-                        {"Id": "m2", "Name": "Movie Two", "Type": "Movie", "Path": "/media/b.mkv"}
-                    ],
                     "TotalRecordCount": 2,
                 }
 
@@ -379,15 +379,11 @@ class TestMediaIndexBuildPaths:
                 self.calls.append(kwargs.get("start_index", 0))
                 if kwargs.get("start_index", 0) == 0:
                     return {
-                        "Items": [
+                        "Items": [{"Id": "m1", "Name": "Movie One", "Type": "Movie", "Path": "/media/a.mkv"}],
-                            {"Id": "m1", "Name": "Movie One", "Type": "Movie", "Path": "/media/a.mkv"}
-                        ],
                         "TotalRecordCount": 2,
                     }
                 return {
-                    "Items": [
+                    "Items": [{"Id": "m2", "Name": "Movie Two", "Type": "Movie", "Path": "/media/b.mkv"}],
-                        {"Id": "m2", "Name": "Movie Two", "Type": "Movie", "Path": "/media/b.mkv"}
-                    ],
                     "TotalRecordCount": 2,
                 }
 

backend/tests/test_services.py

@@ -396,6 +396,77 @@ def test_delete_service_cascades_to_widgets(client, tmp_path):
     assert int(remaining[0]) == 0
 
 
+# ---------------------------------------------------------------------------
+# Harness cascade-delete (Slice 4)
+# ---------------------------------------------------------------------------
+
+
+def test_cascade_delete_removes_harness_data_across_concerns(tmp_path, monkeypatch):
+    """Deleting a service cascades to both qbittorrent samples and media items.
+
+    Proves end-to-end cascade across both harness-managed concerns, and that
+    deleting one service preserves another service's data (multi-instance).
+    """
+    monkeypatch.setenv("BACKEND_CACHE_DIR", str(tmp_path))
+
+    from media_library_viewer_api.services.media_index_impl import MediaIndex
+    from media_library_viewer_api.services.qbittorrent_store import QbittorrentSampleStore
+    from media_library_viewer_api.services.service_data import (
+        get_service_data_harness,
+        reset_service_data_harness,
+    )
+
+    reset_service_data_harness()
+    harness = get_service_data_harness()
+
+    store = SettingsStore(tmp_path / "settings.sqlite")
+    store.ensure_defaults()
+
+    # --- qBit: create service, add samples, delete, verify gone ---
+    qbit_a = store.upsert_service(
+        {"service_type": "qbittorrent", "name": "qA", "config": {"base_url": "http://a"}, "enabled": True}
+    )
+    qbit_b = store.upsert_service(
+        {"service_type": "qbittorrent", "name": "qB", "config": {"base_url": "http://b"}, "enabled": True}
+    )
+    sample_store = QbittorrentSampleStore(harness)
+    sample_store.append(qbit_a["id"], ts=1000, dl_speed=500, up_speed=100)
+    sample_store.append(qbit_b["id"], ts=1000, dl_speed=200, up_speed=50)
+
+    assert len(sample_store.window(qbit_a["id"])) == 1
+    assert len(sample_store.window(qbit_b["id"])) == 1
+
+    store.delete_service(qbit_a["id"])
+
+    assert sample_store.window(qbit_a["id"]) == []
+    assert len(sample_store.window(qbit_b["id"])) == 1  # B survives
+
+    # --- MediaIndex: create services, add items, delete, verify scoped ---
+    jelly_a = store.upsert_service(
+        {"service_type": "jellyfin", "name": "jA", "config": {"base_url": "http://ja"}, "enabled": True}
+    )
+    jelly_b = store.upsert_service(
+        {"service_type": "jellyfin", "name": "jB", "config": {"base_url": "http://jb"}, "enabled": True}
+    )
+    index = MediaIndex(harness.db_path("media_index"))
+    index.init_schema()
+    index.replace_items([{"id": "m1", "title": "A1"}], service_id=jelly_a["id"])
+    index.replace_items([{"id": "m2", "title": "B1"}], service_id=jelly_b["id"])
+
+    rows_a, total_a = index.query(service_id=jelly_a["id"])
+    rows_b, total_b = index.query(service_id=jelly_b["id"])
+    assert total_a == 1 and total_b == 1
+
+    store.delete_service(jelly_a["id"])
+
+    rows_a_after, total_a_after = index.query(service_id=jelly_a["id"])
+    rows_b_after, total_b_after = index.query(service_id=jelly_b["id"])
+    assert total_a_after == 0  # deleted
+    assert total_b_after == 1  # survives
+
+    reset_service_data_harness()
+
+
 # ---------------------------------------------------------------------------
 # Service task run history
 # ---------------------------------------------------------------------------