chore: Add debug logging for missing function call events

This change adds a debug log statement to output the function response IDs and the event list when a matching function call event is not found, which helps in debugging.

Co-authored-by: Hangfei Lin <hangfei@google.com>
PiperOrigin-RevId: 829059186

src/google/adk/flows/llm_flows/contents.py

@@ -15,6 +15,7 @@
 from __future__ import annotations
 
 import copy
+import logging
 from typing import AsyncGenerator
 from typing import Optional
 
@@ -29,6 +30,8 @@ from .functions import remove_client_function_call_id
 from .functions import REQUEST_CONFIRMATION_FUNCTION_CALL_NAME
 from .functions import REQUEST_EUC_FUNCTION_CALL_NAME
 
+logger = logging.getLogger('google_adk.' + __name__)
+
 
 class _ContentLlmRequestProcessor(BaseLlmRequestProcessor):
   """Builds the contents for the LLM request."""
@@ -183,6 +186,12 @@ def _rearrange_events_for_latest_function_response(
           break
 
   if function_call_event_idx == -1:
+    logger.debug(
+        'No function call event found for function responses ids: %s in'
+        ' event list: %s',
+        function_responses_ids,
+        events,
+    )
     raise ValueError(
         'No function call event found for function responses ids:'
         f' {function_responses_ids}'