Update app.py

Fix FAISS thread initialization race condition

app.py

@@ -240,6 +240,9 @@ class ProductionFAISSIndex:
         self.texts = texts
         self._lock = threading.RLock()
         
+        # FIXED: Initialize shutdown event BEFORE starting thread
+        self._shutdown = threading.Event()
+        
         # Single writer thread (no concurrent write conflicts)
         self._write_queue: Queue = Queue()
         self._writer_thread = threading.Thread(
@@ -247,13 +250,11 @@ class ProductionFAISSIndex:
             daemon=True,
             name="FAISSWriter"
         )
-        self._writer_thread.start()
+        self._writer_thread.start()  # ← Only start ONCE, AFTER _shutdown exists
         
         # ProcessPool for encoding (avoids GIL + memory leaks)
         self._encoder_pool = ProcessPoolExecutor(max_workers=2)
         
-        self._shutdown = threading.Event()
-        
         logger.info(
             f"Initialized ProductionFAISSIndex with {len(texts)} vectors, "
             f"single-writer pattern"