fix: avoid UserWarning in _build_response_log when response has funct…

Merge google#6127

# Fix: `_build_response_log()` triggers genai SDK UserWarning on every tool call

Closes google#4685

## What's the problem?

Every time an ADK agent invokes a tool, the debug logger calls `_build_response_log(response)`, which includes `resp.text` in its f-string:

```python
return f"""
LLM Response:
...
Text:
{resp.text}   # ← triggers UserWarning
...
"""
```

The `GenerateContentResponse.text` property in the google-genai SDK raises a `UserWarning` whenever the response contains non-text parts — which is exactly the case when the model responds with a `function_call`. This means **every single tool invocation floods the log with warnings** like:

```
UserWarning: Warning: there are non-text parts in the response: ['function_call'],returning concatenated text result from text parts, check `response.parts` directly to inspect non-text parts
  warnings.warn(
```

Since `_build_response_log` is only called inside `if logger.isEnabledFor(logging.DEBUG)`, this hits any developer who enables debug logging — which is common when debugging agents.

## Root cause

`GenerateContentResponse.text` is a convenience property that warns when mixed content is present. Accessing it in a log formatter silently poisons the log output whenever agents use tools.

## Fix

Replace `resp.text` with a manual join of only the text parts from `resp.candidates`, bypassing the warning entirely:

```python
# Before
return f"""
...
Text:
{resp.text}
...
"""

# After — safe extraction with no warning
text_parts = []
if resp.candidates:
    for candidate in resp.candidates:
        if candidate.content and candidate.content.parts:
            text_parts.extend(
                p.text for p in candidate.content.parts if p.text is not None
            )
text = ''.join(text_parts)

return f"""
...
Text:
{text}
...
"""
```

This produces identical output when only text parts are present, and correctly shows an empty string (rather than a warning) when the response is a function call — which is the right behavior for a debug log.

## Files changed

- `src/google/adk/models/google_llm.py` — 10-line change inside `_build_response_log()`, no other logic touched

Co-authored-by: Yifan Wang <wanyif@google.com>
COPYBARA_INTEGRATE_REVIEW=google#6127 from AdeevMardia2008:fix/response-log-text-warning 011c153
PiperOrigin-RevId: 933440866

Author: 2 people

src/google/adk/models/google_llm.py

@@ -614,11 +614,30 @@ def _build_response_log(resp: types.GenerateContentResponse) -> str:
       function_calls_text.append(
           f'name: {func_call.name}, args: {func_call.args}'
       )
+  # Avoid accessing resp.text directly: the genai SDK raises a UserWarning
+  # whenever .text is accessed on a response that contains non-text parts
+  # (e.g. function_call). This floods logs on every tool invocation.
+  # Instead, manually join only the text parts from candidates.
+  text_parts = []
+  # Mimic resp.text behavior exactly but without triggering linter warnings:
+  # 1. Only use the first candidate.
+  # 2. Exclude thought/reasoning parts.
+  if (
+      resp.candidates
+      and resp.candidates[0].content
+      and resp.candidates[0].content.parts
+  ):
+    for part in resp.candidates[0].content.parts:
+      if isinstance(part.text, str):
+        if getattr(part, 'thought', False):
+          continue
+        text_parts.append(part.text)
+  text = ''.join(text_parts)
   return f"""
 LLM Response:
 -----------------------------------------------------------
 Text:
-{resp.text}
+{text}
 -----------------------------------------------------------
 Function calls:
 {_NEW_LINE.join(function_calls_text)}