feat(settings): add "Rebuild semantic index" maintenance action

Drops and recreates the sqlite-vec tables at the current model dimension, then
re-queues every image for embedding. Fixes "dimension mismatch" search errors
that occur when the vector table was built for a different model/dimension (e.g.
after experimenting with 768-dim models against this 512-dim build).

The rebuild runs under the embedding worker's DB write lock and resets the job
queue inside a single transaction, so it can't interleave with an in-flight
embedding batch (per code review).

src-tauri/src/commands.rs

@@ -1987,6 +1987,14 @@ pub async fn vacuum_database(
     })
 }
 
+#[tauri::command]
+pub async fn rebuild_semantic_index(db: State<'_, DbState>) -> Result<usize, String> {
+    let conn = db.get().map_err(|e| e.to_string())?;
+    // Serialize against the embedding worker (which writes under the same lock)
+    // so the rebuild can't interleave with an in-flight embedding batch.
+    indexer::with_db_write_lock(|| db::reset_all_embeddings(&conn)).map_err(|e| e.to_string())
+}
+
 #[derive(serde::Serialize)]
 pub struct OrphanedThumbnailsInfo {
     pub count: u64,

src-tauri/src/db.rs

@@ -496,6 +496,41 @@ pub fn repair_embedding_consistency(conn: &Connection) -> Result<(usize, usize)>
     Ok((orphaned_vectors, missing_vector_ids.len()))
 }
 
+/// Full semantic-index rebuild: recreate the vector tables at the current model
+/// dimension and re-queue every image for embedding. Used by the maintenance
+/// action when the index is stale or its dimension no longer matches the model
+/// (which otherwise surfaces as a "dimension mismatch" search error). Returns the
+/// number of images re-queued.
+pub fn reset_all_embeddings(conn: &Connection) -> Result<usize> {
+    // Recreate the vector tables at the current model dimension first (DDL, kept
+    // out of the transaction below). The caller holds the DB write lock, so the
+    // embedding worker can't interleave a write between this and the queue reset.
+    vector::rebuild_tables(conn)?;
+    let tx = conn.unchecked_transaction()?;
+    tx.execute(
+        "UPDATE images
+         SET embedding_status = 'pending',
+             embedding_model = NULL,
+             embedding_updated_at = NULL,
+             embedding_error = NULL",
+        [],
+    )?;
+    tx.execute("DELETE FROM embedding_jobs", [])?;
+    let queued = tx.execute(
+        "INSERT INTO embedding_jobs (image_id, status, attempts, last_error, created_at, updated_at)
+         SELECT id, 'pending', 0, NULL, datetime('now'), datetime('now')
+         FROM images",
+        [],
+    )?;
+    tx.execute(
+        "INSERT INTO app_kv (key, value) VALUES ('embedding_revision', 1)
+         ON CONFLICT(key) DO UPDATE SET value = value + 1",
+        [],
+    )?;
+    tx.commit()?;
+    Ok(queued)
+}
+
 pub fn retry_failed_embedding_jobs(conn: &Connection, folder_id: i64) -> Result<usize> {
     // Only re-queue images that are actually embeddable right now.
     // Videos without a thumbnail would just fail again immediately, so skip them —

src-tauri/src/indexer.rs

@@ -1288,7 +1288,7 @@ fn max_worker_fetch_size(active_folders: &HashSet<i64>) -> usize {
         .unwrap_or(StorageProfile::Balanced.worker_fetch_size())
 }
 
-fn with_db_write_lock<T>(operation: impl FnOnce() -> Result<T>) -> Result<T> {
+pub fn with_db_write_lock<T>(operation: impl FnOnce() -> Result<T>) -> Result<T> {
     let lock = DB_WRITE_LOCK.get_or_init(|| Mutex::new(()));
     let _guard = lock.lock().unwrap();
     operation()

src-tauri/src/lib.rs

@@ -192,6 +192,7 @@ pub fn run() {
             commands::open_app_data_folder,
             commands::get_database_info,
             commands::vacuum_database,
+            commands::rebuild_semantic_index,
             commands::get_orphaned_thumbnails_info,
             commands::cleanup_orphaned_thumbnails,
             commands::get_muted_folder_ids,

src-tauri/src/vector.rs

@@ -36,6 +36,18 @@ pub fn migrate(conn: &Connection) -> Result<()> {
     Ok(())
 }
 
+/// Drop and recreate the vector tables at the current `CLIP_VECTOR_DIM`. Used by
+/// the "Rebuild semantic index" maintenance action when stored vectors no longer
+/// match the active model's dimension (e.g. after switching embedding models),
+/// so the columns are rebuilt to the right size before embeddings regenerate.
+pub fn rebuild_tables(conn: &Connection) -> Result<()> {
+    conn.execute_batch(
+        "DROP TABLE IF EXISTS image_vec;
+         DROP TABLE IF EXISTS caption_vec;",
+    )?;
+    migrate(conn)
+}
+
 #[allow(dead_code)]
 pub fn delete_embedding(conn: &Connection, image_id: i64) -> Result<()> {
     conn.execute("DELETE FROM image_vec WHERE image_id = ?1", [image_id])?;

src/components/SettingsModal.tsx

@@ -138,6 +138,8 @@ export function SettingsModal() {
   const [dbInfo, setDbInfo] = useState<DatabaseInfo | null>(null);
   const [vacuuming, setVacuuming] = useState(false);
   const [vacuumResult, setVacuumResult] = useState<VacuumResult | null>(null);
+  const [rebuildingIndex, setRebuildingIndex] = useState(false);
+  const [rebuildIndexResult, setRebuildIndexResult] = useState<string | null>(null);
   const [thumbnailInfo, setThumbnailInfo] = useState<OrphanedThumbnailsInfo | null>(null);
   const [cleaningThumbnails, setCleaningThumbnails] = useState(false);
   const [thumbnailCleanupResult, setThumbnailCleanupResult] = useState<CleanupOrphanedThumbnailsResult | null>(null);
@@ -184,6 +186,7 @@ export function SettingsModal() {
   const setNotificationsPaused = useGalleryStore((state) => state.setNotificationsPaused);
   const getDatabaseInfo = useGalleryStore((state) => state.getDatabaseInfo);
   const vacuumDatabase = useGalleryStore((state) => state.vacuumDatabase);
+  const rebuildSemanticIndex = useGalleryStore((state) => state.rebuildSemanticIndex);
   const getOrphanedThumbnailsInfo = useGalleryStore((state) => state.getOrphanedThumbnailsInfo);
   const cleanupOrphanedThumbnails = useGalleryStore((state) => state.cleanupOrphanedThumbnails);
   const appVersion = useGalleryStore((state) => state.appVersion);
@@ -799,6 +802,42 @@ export function SettingsModal() {
                     </button>
                   </SettingsItem>
 
+                  <SettingsItem
+                    label="Rebuild semantic index"
+                    description={
+                      <>
+                        <span>
+                          Recreates the visual-embedding index and re-embeds every image in the
+                          background. Use this if semantic or similar-image search reports a
+                          dimension-mismatch error (for example after experimenting with a
+                          different embedding model).
+                        </span>
+                        {rebuildIndexResult !== null ? (
+                          <span className="mt-2 block text-gray-600">{rebuildIndexResult}</span>
+                        ) : null}
+                      </>
+                    }
+                  >
+                    <button
+                      className="rounded-md border border-white/10 bg-white/[0.055] px-3 py-1.5 text-xs text-gray-300 transition-colors hover:bg-white/10 hover:text-white disabled:cursor-not-allowed disabled:opacity-45 light-theme:border-gray-700/50 light-theme:bg-gray-900 light-theme:text-white light-theme:hover:bg-gray-800 light-theme:hover:text-white"
+                      onClick={() => {
+                        setRebuildingIndex(true);
+                        setRebuildIndexResult(null);
+                        void rebuildSemanticIndex()
+                          .then((count) =>
+                            setRebuildIndexResult(
+                              `Re-queued ${count.toLocaleString()} image${count === 1 ? "" : "s"} for embedding.`,
+                            ),
+                          )
+                          .catch((error) => setRebuildIndexResult(String(error)))
+                          .finally(() => setRebuildingIndex(false));
+                      }}
+                      disabled={rebuildingIndex}
+                    >
+                      {rebuildingIndex ? "Rebuilding…" : "Rebuild index"}
+                    </button>
+                  </SettingsItem>
+
                   <SettingsItem
                     label="Thumbnail cache"
                     description={

src/store.ts

@@ -467,6 +467,7 @@ interface GalleryState {
   openAppDataFolder: () => Promise<void>;
   getDatabaseInfo: () => Promise<DatabaseInfo>;
   vacuumDatabase: () => Promise<VacuumResult>;
+  rebuildSemanticIndex: () => Promise<number>;
   getOrphanedThumbnailsInfo: () => Promise<OrphanedThumbnailsInfo>;
   cleanupOrphanedThumbnails: () => Promise<CleanupOrphanedThumbnailsResult>;
   retryFailedEmbeddings: (folderId: number) => Promise<void>;
@@ -1858,6 +1859,8 @@ export const useGalleryStore = create<GalleryState>((set, get) => ({
 
   vacuumDatabase: () => invoke<VacuumResult>("vacuum_database"),
 
+  rebuildSemanticIndex: () => invoke<number>("rebuild_semantic_index"),
+
   getOrphanedThumbnailsInfo: () => invoke<OrphanedThumbnailsInfo>("get_orphaned_thumbnails_info"),
 
   cleanupOrphanedThumbnails: () => invoke<CleanupOrphanedThumbnailsResult>("cleanup_orphaned_thumbnails"),