fix: pre-empt review findings before next push

- hnsw_index: fetch folder embedding IDs before acquiring the read lock
  in find_similar_image_matches; holding the lock across a SQLite query
  was delaying concurrent ensure_index write-lock requests

- store/DuplicateFinder: add duplicateScanError state; scanDuplicates
  now catches errors and stores them rather than silently leaving the
  user with empty results and no feedback

src-tauri/src/hnsw_index.rs

@@ -103,16 +103,29 @@ pub fn find_similar_image_matches(
         None => return Ok(Vec::new()),
     };
 
+    // Fetch folder image IDs *before* acquiring the read lock so we don't hold
+    // the lock across a potentially slow SQLite query, which would delay any
+    // concurrent ensure_index call waiting for a write lock.
+    let folder_image_ids: Option<Vec<i64>> = if let Some(folder_id) = folder_id {
+        let ids = vector::get_all_image_embeddings_with_ids(conn, Some(folder_id))?
+            .into_iter()
+            .map(|(id, _)| id)
+            .collect();
+        Some(ids)
+    } else {
+        None
+    };
+
     let guard = cache().read().expect("hnsw cache poisoned");
     let Some(cached) = guard.as_ref() else {
         return Ok(Vec::new());
     };
 
     let knbn = (offset + limit).max(limit).saturating_add(32);
-    let neighbours: Vec<Neighbour> = if let Some(folder_id) = folder_id {
-        let mut allowed_ids = vector::get_all_image_embeddings_with_ids(conn, Some(folder_id))?
+    let neighbours: Vec<Neighbour> = if let Some(image_ids) = folder_image_ids {
+        let mut allowed_ids = image_ids
             .into_iter()
-            .filter_map(|(allowed_image_id, _)| {
+            .filter_map(|allowed_image_id| {
                 cached.external_by_image_id.get(&allowed_image_id).copied()
             })
             .collect::<Vec<_>>();

src/components/DuplicateFinder.tsx

@@ -116,6 +116,7 @@ export function DuplicateFinder() {
   const duplicateGroups = useGalleryStore((state) => state.duplicateGroups);
   const duplicateScanning = useGalleryStore((state) => state.duplicateScanning);
   const duplicateScanProgress = useGalleryStore((state) => state.duplicateScanProgress);
+  const duplicateScanError = useGalleryStore((state) => state.duplicateScanError);
   const duplicateSelectedIds = useGalleryStore((state) => state.duplicateSelectedIds);
   const duplicateLastScanned = useGalleryStore((state) => state.duplicateLastScanned);
   const selectedFolderId = useGalleryStore((state) => state.selectedFolderId);
@@ -228,6 +229,9 @@ export function DuplicateFinder() {
           </div>
         ) : null}
 
+        {duplicateScanError ? (
+          <p className="mt-2 text-[11px] text-red-400/80">{duplicateScanError}</p>
+        ) : null}
         {deleteResult ? (
           <p className="mt-2 text-[11px] text-white/40">{deleteResult}</p>
         ) : null}

src/store.ts

@@ -278,6 +278,7 @@ interface GalleryState {
   duplicateGroups: DuplicateGroup[];
   duplicateScanning: boolean;
   duplicateScanProgress: { scanned: number; total: number } | null;
+  duplicateScanError: string | null;
   duplicateSelectedIds: Set<number>;
   duplicateLastScanned: number | null; // Unix timestamp (seconds)
   duplicateScanFolderId: number | null | undefined; // undefined = never scanned
@@ -613,6 +614,7 @@ export const useGalleryStore = create<GalleryState>((set, get) => ({
   duplicateGroups: [],
   duplicateScanning: false,
   duplicateScanProgress: null,
+  duplicateScanError: null,
   duplicateSelectedIds: new Set(),
   duplicateLastScanned: null,
   duplicateScanFolderId: undefined,
@@ -1466,7 +1468,7 @@ export const useGalleryStore = create<GalleryState>((set, get) => ({
 
   scanDuplicates: async (folderId = null) => {
     const { listen } = await import("@tauri-apps/api/event");
-    set({ duplicateScanning: true, duplicateGroups: [], duplicateScanProgress: null, duplicateSelectedIds: new Set() });
+    set({ duplicateScanning: true, duplicateGroups: [], duplicateScanProgress: null, duplicateScanError: null, duplicateSelectedIds: new Set() });
     const unlisten = await listen<[number, number]>("duplicate_scan_progress", (event) => {
       const [scanned, total] = event.payload;
       set({ duplicateScanProgress: { scanned, total } });
@@ -1478,6 +1480,8 @@ export const useGalleryStore = create<GalleryState>((set, get) => ({
         "Duplicate scan complete",
         groups.length === 1 ? "Found 1 duplicate group." : `Found ${groups.length.toLocaleString()} duplicate groups.`,
       );
+    } catch (e) {
+      set({ duplicateScanError: String(e) });
     } finally {
       unlisten();
       set({ duplicateScanning: false });