feat(service-storage-harness): slice 3 — migrate MediaIndex onto harness (scoped replace_items, +service_id)

Register MediaIndex as a harness concern with ALTER TABLE migration to add
service_id column (idempotent). Scope replace_items by service_id (FIXES latent
global-clear bug where building for one Jellyfin wiped another's rows). Scope
query by service_id (empty-string = all rows, backward-compat). Thread
service_id through build_media_index + worker + query_media router. New
regression test proves scoped replace preserves other services' rows.

Backend: 321 pytest pass, ruff clean. Frontend: build green.

backend/src/media_library_viewer_api/routers/media.py

@@ -282,6 +282,7 @@ def query_media(
     sort_order: str = Query("Ascending", description="Ascending or Descending"),
     limit: int = Query(100, ge=1, le=1000),
     offset: int = Query(0, ge=0),
+    jellyfin_service_id: str | None = None,
     client: JellyfinClient = Depends(get_jellyfin_client),
     user_id: str = Depends(get_user_id),
     index: MediaIndex = Depends(get_media_index),
@@ -316,6 +317,7 @@ def query_media(
         sort_order=sort_order,
         limit=limit,
         offset=offset,
+        service_id=jellyfin_service_id or "",
     )
 
     logger.info("Media query returned total=%s rows=%s", total, len(rows))

backend/src/media_library_viewer_api/services/media_index_impl.py

@@ -17,6 +17,7 @@ from typing import Any, Callable, Iterable
 from media_library_viewer_api.clients.jellyfin import JellyfinClient
 from media_library_viewer_api.domain.media import display_media_row, normalize_media_item
 from media_library_viewer_api.path_utils import resolve_remote_media_path
+from media_library_viewer_api.services.service_data import StorageConcern
 
 logger = logging.getLogger(__name__)
 
@@ -25,6 +26,20 @@ logger = logging.getLogger(__name__)
 DEFAULT_INDEX_PATH = Path(".cache/media_library_viewer/media_index.sqlite")
 MEDIA_TYPES = "Movie,Episode,Video"
 
+# Harness concern registration: the media_index DB is scoped by service_id so
+# multiple Jellyfin instances can coexist. The ALTER TABLE migration adds the
+# service_id column to existing DBs; init_schema adds it for fresh installs.
+# The harness run_migrations catches "duplicate column name" on re-runs.
+MEDIA_INDEX_CONCERN = StorageConcern(
+    concern_key="media_index",
+    db_filename=DEFAULT_INDEX_PATH.name,
+    migrations=[
+        "ALTER TABLE media_items ADD COLUMN service_id TEXT NOT NULL DEFAULT ''",
+    ],
+    tables=["media_items"],
+    service_id_column="service_id",
+)
+
 # Only values from this whitelist are interpolated into ORDER BY. User-selected
 # sort keys map to these known SQL snippets to avoid SQL injection.
 SORT_COLUMNS = {
@@ -135,7 +150,8 @@ class MediaIndex:
                     date_added_ts INTEGER,
                     path TEXT,
                     library_id TEXT,
-                    library_name TEXT
+                    library_name TEXT,
+                    service_id TEXT NOT NULL DEFAULT ''
                 );
                 CREATE TABLE IF NOT EXISTS index_metadata (
                     key TEXT PRIMARY KEY,
@@ -167,8 +183,13 @@ class MediaIndex:
                 (key, str(value)),
             )
 
-    def replace_items(self, rows: Iterable[dict[str, Any]]) -> int:
-        """Atomically replace indexed media rows with a freshly built set."""
+    def replace_items(self, rows: Iterable[dict[str, Any]], service_id: str = "") -> int:
+        """Atomically replace indexed media rows with a freshly built set.
+
+        Scoped by ``service_id``: only rows belonging to this service are
+        deleted before the new batch is inserted. This means building for one
+        Jellyfin instance no longer wipes another instance's rows.
+        """
         self.init_schema()
         row_list = list(rows)
         columns = [
@@ -194,13 +215,14 @@ class MediaIndex:
             "path",
             "library_id",
             "library_name",
+            "service_id",
         ]
         placeholders = ",".join(["?"] * len(columns))
         with self.connect() as conn:
-            conn.execute("DELETE FROM media_items")
+            conn.execute("DELETE FROM media_items WHERE service_id = ?", (service_id,))
             conn.executemany(
                 f"INSERT OR REPLACE INTO media_items ({','.join(columns)}) VALUES ({placeholders})",
-                [[row.get(column) for column in columns] for row in row_list],
+                [[row.get(column) if column != "service_id" else service_id for column in columns] for row in row_list],
             )
             conn.execute(
                 "INSERT OR REPLACE INTO index_metadata (key, value) VALUES ('updated_at', ?)",
@@ -287,8 +309,14 @@ class MediaIndex:
         sort_order: str = "Ascending",
         limit: int = 100,
         offset: int = 0,
+        service_id: str = "",
     ) -> tuple[list[dict[str, Any]], int]:
-        """Query indexed media with full-index filters, sorting, and pagination."""
+        """Query indexed media with full-index filters, sorting, and pagination.
+
+        When ``service_id`` is non-empty, only rows matching that service are
+        returned. When empty (the default), all rows are returned (backward-
+        compatible with callers that are not multi-instance aware).
+        """
         self.init_schema()
         where = []
         params: list[Any] = []
@@ -309,6 +337,9 @@ class MediaIndex:
             where.append("hdr = 1")
         elif hdr_filter == "SDR/unknown only":
             where.append("(hdr IS NULL OR hdr = 0)")
+        if service_id:
+            where.append("service_id = ?")
+            params.append(service_id)
 
         where_sql = " WHERE " + " AND ".join(where) if where else ""
         sort_sql = SORT_COLUMNS.get(sort_key, SORT_COLUMNS["title"])
@@ -338,6 +369,7 @@ def build_media_index(
     fallback_prefix: str = "",
     progress_callback: Callable[[dict[str, Any]], None] | None = None,
     should_cancel: Callable[[], bool] | None = None,
+    service_id: str = "",
 ) -> int:
     """Fetch Jellyfin pages for all selected libraries and rebuild the index."""
     index = index or MediaIndex()
@@ -453,7 +485,7 @@ def build_media_index(
     logger.info("Media index finalizing rows=%s", len(normalized_rows))
     emit("finalizing", "Writing index to disk")
     ensure_not_cancelled()
-    count = index.replace_items(normalized_rows)
+    count = index.replace_items(normalized_rows, service_id=service_id)
     duration = time.perf_counter() - started_at
     index.set_metadata("build_duration_seconds", f"{duration:.3f}")
     processed_total = count

backend/src/media_library_viewer_api/services/service_data.py

@@ -143,6 +143,10 @@ def get_service_data_harness() -> ServiceDataHarness:
         from media_library_viewer_api.services.qbittorrent_store import QBITTORRENT_CONCERN
 
         _HARNESS.register(QBITTORRENT_CONCERN)
+
+        from media_library_viewer_api.services.media_index_impl import MEDIA_INDEX_CONCERN
+
+        _HARNESS.register(MEDIA_INDEX_CONCERN)
         _HARNESS.run_migrations()
     return _HARNESS
 

backend/src/media_library_viewer_api/workers/media_index_worker.py

@@ -174,6 +174,7 @@ def run_build(final_index_path: str | Path, staging_index_path: str | Path, serv
             fallback_prefix=settings.path_prefix,
             progress_callback=lambda state: _progress_callback(final_index, pid, state),
             should_cancel=lambda: _cancel_requested(final_index),
+            service_id=service_id,
         )
         # Swap the staging database into place atomically.
         os.replace(staging_index.db_path, final_index.db_path)