diff --git a/backend/src/media_library_viewer_api/routers/media.py b/backend/src/media_library_viewer_api/routers/media.py
index eda060e..e4174c1 100644
--- a/backend/src/media_library_viewer_api/routers/media.py
+++ b/backend/src/media_library_viewer_api/routers/media.py
@@ -133,20 +133,27 @@ def get_index_status(index: MediaIndex = Depends(get_media_index)) -> dict[str,
 
 @router.post("/build", status_code=status.HTTP_202_ACCEPTED)
 def post_build_index(
-    client: JellyfinClient = Depends(get_jellyfin_client),
-    user_id: str = Depends(get_user_id),
     jellyfin_service_id: str | None = None,
     index: MediaIndex = Depends(get_media_index),
 ) -> dict[str, Any]:
-    """Start a media index build in a subprocess worker."""
+    """Start a media index build in a subprocess worker.
+
+    The worker resolves its own Jellyfin connection from the settings store.
+    We do NOT use Depends(get_jellyfin_client) here because the worker runs
+    in a separate process and needs to resolve the client itself. Validating
+    the connection here would fail if Jellyfin is briefly unreachable, even
+    though the build just needs to start the worker process.
+    """
     with _build_lock:
         current_status = _clean_stale_build_state(index)
         if current_status.build_running and _pid_is_alive(current_status.build_pid):
             logger.warning("Media build already running pid=%s", current_status.build_pid)
             raise HTTPException(status_code=status.HTTP_409_CONFLICT, detail="Media index build already in progress")
 
-        libraries = client.libraries(user_id)
-        logger.info("Starting media index build user_id=%s libraries=%s", user_id, len(libraries))
+        logger.info(
+            "Starting media index build service_id=%s",
+            jellyfin_service_id or "<default>",
+        )
         process = _start_worker(index, jellyfin_service_id or "")
         _set_build_metadata(
             index,
@@ -159,7 +166,7 @@ def post_build_index(
                 "build_items_total": 0,
                 "build_current_library": "",
                 "build_library_index": 0,
-                "build_libraries_total": len(libraries),
+                "build_libraries_total": 0,
                 "build_library_progress": None,
                 "build_library_items_processed": 0,
                 "build_library_items_total": 0,
diff --git a/backend/tests/test_api.py b/backend/tests/test_api.py
index ba29134..42fde98 100644
--- a/backend/tests/test_api.py
+++ b/backend/tests/test_api.py
@@ -363,7 +363,7 @@ class TestMediaIndexApi:
                 assert data["status"] == "started"
                 assert data["build_running"] is True
                 assert data["build_stage"] == "queued"
-                assert data["build_libraries_total"] == len(mock_jellyfin.libraries.return_value)
+                assert data["build_libraries_total"] == 0
                 assert data["build_pid"] == 4321
                 start_worker.assert_called_once()
             finally:
diff --git a/frontend/src/components/WidgetConfigDialog.tsx b/frontend/src/components/WidgetConfigDialog.tsx
index 90b8a66..ef341a4 100644
--- a/frontend/src/components/WidgetConfigDialog.tsx
+++ b/frontend/src/components/WidgetConfigDialog.tsx
@@ -237,8 +237,9 @@ export function WidgetConfigDialog({
 	useEffect(() => {
 		if (open && editWidgetId) {
 			// Search both owned widgets and referenced widgets.
-			const target = instances.find((w) => w.id === editWidgetId)
-				?? references.find((r) => r.widget.id === editWidgetId)?.widget;
+			const target =
+				instances.find((w) => w.id === editWidgetId) ??
+				references.find((r) => r.widget.id === editWidgetId)?.widget;
 			if (target) {
 				startEdit(target);
 			}
diff --git a/frontend/src/hooks/useMedia.ts b/frontend/src/hooks/useMedia.ts
index 2b89d7a..5a9577f 100644
--- a/frontend/src/hooks/useMedia.ts
+++ b/frontend/src/hooks/useMedia.ts
@@ -54,6 +54,10 @@ export function useBuildIndex(jellyfinServiceId?: string) {
 		onSuccess: () => {
 			invalidateMedia(queryClient);
 		},
+		onError: () => {
+			// Invalidate status so the UI reflects the current (non-building) state.
+			invalidateMedia(queryClient);
+		},
 	});
 }
 
diff --git a/frontend/src/pages/service-tabs/MediaTab.tsx b/frontend/src/pages/service-tabs/MediaTab.tsx
index 74097a7..3c972d9 100644
--- a/frontend/src/pages/service-tabs/MediaTab.tsx
+++ b/frontend/src/pages/service-tabs/MediaTab.tsx
@@ -352,6 +352,11 @@ export function MediaTab({ instance }: { instance: ServiceInstance }) {
 				>
 					{buildIndex.isPending || buildRunning ? "Building..." : "Build index"}
 				</Button>
+				{buildIndex.isError ? (
+					<span className="text-sm text-destructive">
+						Build failed: {buildIndex.error instanceof Error ? buildIndex.error.message : "Unknown error"}
+					</span>
+				) : null}
 				{buildRunning && (
 					<>
 						<Button