check for doubles

main.py

@@ -214,6 +214,14 @@ async def delete_book_api(book_id: int):
     return {"ok": ok, "message": message}
 
 
+@app.get("/api/debug/calibre_books")
+async def debug_calibre_books():
+    """Return raw listbooks sample so we can verify field names and structure."""
+    cfg = config.load()
+    books = fetch_all_books(cfg.calibre)
+    return {"total": len(books), "sample": books[:5]}
+
+
 # --- Data reset ---
 
 @app.post("/settings/reset-sync-data")