Fix unintended user message text that triggers content filters (Closes #4249)

src/google/adk/models/lite_llm.py

@@ -98,6 +98,9 @@
 # 1. FinishReason.TOOL_CALL enum does not exist (as of google-genai 0.8.0)
 # 2. Tool calls represent normal completion (model stopped to invoke tools)
 # 3. Gemini native responses use STOP for tool calls (see lite_llm.py:910)
+# 4. Mapping tool-related finish reasons to STOP preserves backward
+#    compatibility with existing ADK consumers that assume STOP
+#    indicates a successful, non-error completion.
 _FINISH_REASON_MAPPING = {
     "length": types.FinishReason.MAX_TOKENS,
     "stop": types.FinishReason.STOP,
@@ -131,6 +134,10 @@
     "before a response was recorded)."
 )
 
+_FALLBACK_USER_CONTENT_TEXT = (
+    "Handle the incoming request according to the provided requirements."
+)
+
 _LITELLM_IMPORTED = False
 _LITELLM_GLOBAL_SYMBOLS = (
     "ChatCompletionAssistantMessage",
@@ -489,22 +496,13 @@ def _append_fallback_user_content_if_missing(
       if not parts:
         content.parts = []
       content.parts.append(
-          types.Part.from_text(
-              text="Handle the requests as specified in the System Instruction."
-          )
+          types.Part.from_text(text=_FALLBACK_USER_CONTENT_TEXT)
       )
       return
   llm_request.contents.append(
       types.Content(
           role="user",
-          parts=[
-              types.Part.from_text(
-                  text=(
-                      "Handle the requests as specified in the System"
-                      " Instruction."
-                  )
-              ),
-          ],
+          parts=[types.Part.from_text(text=_FALLBACK_USER_CONTENT_TEXT)],
       )
   )
 

tests/unittests/models/test_litellm.py

@@ -25,6 +25,7 @@
 import warnings
 
 from google.adk.models.lite_llm import _content_to_message_param
+from google.adk.models.lite_llm import _FALLBACK_USER_CONTENT_TEXT
 from google.adk.models.lite_llm import _FILE_ID_REQUIRED_PROVIDERS
 from google.adk.models.lite_llm import _FINISH_REASON_MAPPING
 from google.adk.models.lite_llm import _function_declaration_to_tool_param
@@ -978,16 +979,13 @@ async def test_generate_content_async_adds_fallback_user_message(
       message for message in kwargs["messages"] if message["role"] == "user"
   ]
   assert any(
-      message.get("content")
-      == "Handle the requests as specified in the System Instruction."
+      message.get("content") == _FALLBACK_USER_CONTENT_TEXT
       for message in user_messages
   )
   assert (
       sum(1 for content in llm_request.contents if content.role == "user") == 1
   )
-  assert llm_request.contents[-1].parts[0].text == (
-      "Handle the requests as specified in the System Instruction."
-  )
+  assert llm_request.contents[-1].parts[0].text == _FALLBACK_USER_CONTENT_TEXT
 
 
 litellm_append_user_content_test_cases = [