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])?;