fix: prefill queue handler async task should not silently error (#442)

examples/llm/components/prefill_worker.py

@@ -16,6 +16,7 @@
 
 import asyncio
 import os
+import sys
 
 from pydantic import BaseModel
 from utils.nixl import NixlMetadataStore
@@ -84,7 +85,16 @@ class PrefillWorker:
         self._metadata_store = NixlMetadataStore("dynamo", runtime)
         await self._metadata_store.put(metadata.engine_id, metadata)
         task = asyncio.create_task(self.prefill_queue_handler())
-        task.add_done_callback(lambda _: print("prefill queue handler created"))
+
+        def prefill_queue_handler_cb(fut):
+            try:
+                fut.result()
+                print("prefill queue handler exited successfully")
+            except Exception as e:
+                print(f"[ERROR] prefill queue handler failed: {e!r}")
+                sys.exit(1)
+
+        task.add_done_callback(prefill_queue_handler_cb)
         print("PrefillWorker initialized")
 
     async def prefill_queue_handler(self):