check for doubles

sync.py

@@ -64,6 +64,14 @@ def run_sync(limit: int | None = None) -> None:
         total_batches = -(-len(new_zips) // batch_size)  # ceiling division
         client = CalibreClient(cfg.calibre)
 
+        # Pre-load existing book titles so duplicate detection doesn't need per-book OPDS searches
+        try:
+            from uploader import fetch_all_books
+            existing = fetch_all_books(cfg.calibre)
+            client.preload_existing_titles(existing)
+        except Exception as exc:
+            log.warning("Could not pre-load existing books (%s) — will fall back to per-book OPDS search", exc)
+
         for batch_num, i in enumerate(range(0, len(new_zips), batch_size), start=1):
             chunk = new_zips[i : i + batch_size]
             log.info("Batch %d/%d — processing %d zip(s)", batch_num, total_batches, len(chunk))