From 22344c37a90014c115cc0b1c73a9d777604ce784 Mon Sep 17 00:00:00 2001
From: Enjoy Kumawat <ekumawat54@gmail.com>
Date: Wed, 8 Apr 2026 10:03:06 +0530
Subject: [PATCH 1/2] fix: warn on silent MIME type fallback and propagate
 model in recursive calls

LiteLLM silently fell back to application/octet-stream when file_uri
MIME type could not be determined, using only a debug log that was easy
to miss. Upgrade to warning level so developers notice the fallback.

Also fix _content_to_message_param() to propagate the model parameter
in recursive calls for mixed function_response + content parts, which
caused incorrect provider detection on Vertex AI / Anthropic.

Fixes #5184
---
 src/google/adk/models/lite_llm.py      |  3 +-
 tests/unittests/models/test_litellm.py | 53 ++++++++++++++++++++++++++
 2 files changed, 55 insertions(+), 1 deletion(-)

diff --git a/src/google/adk/models/lite_llm.py b/src/google/adk/models/lite_llm.py
index 7d13696c96..e3803b8da9 100644
--- a/src/google/adk/models/lite_llm.py
+++ b/src/google/adk/models/lite_llm.py
@@ -811,6 +811,7 @@ async def _content_to_message_param(
     follow_up = await _content_to_message_param(
         types.Content(role=content.role, parts=non_tool_parts),
         provider=provider,
+        model=model,
     )
     follow_up_messages = (
         follow_up if isinstance(follow_up, list) else [follow_up]
@@ -1091,7 +1092,7 @@ async def _get_content(
       if not mime_type:
         # LiteLLM's Vertex AI backend requires format for GCS URIs.
         mime_type = _DEFAULT_MIME_TYPE
-        logger.debug(
+        logger.warning(
             "Could not determine MIME type for file_uri %s, using default: %s",
             part.file_data.file_uri,
             mime_type,
diff --git a/tests/unittests/models/test_litellm.py b/tests/unittests/models/test_litellm.py
index ace08ad997..891bf4f984 100644
--- a/tests/unittests/models/test_litellm.py
+++ b/tests/unittests/models/test_litellm.py
@@ -4894,3 +4894,56 @@ async def test_content_to_message_param_anthropic_no_signature_falls_back():
   # Falls back to reasoning_content when no signatures present
   assert result.get("reasoning_content") == "thinking without sig"
   assert "thinking_blocks" not in result
+
+
+@pytest.mark.asyncio
+async def test_content_to_message_param_file_uri_mime_fallback_logs_warning(
+    caplog,
+):
+  """Test that falling back to application/octet-stream logs a warning."""
+  file_part = types.Part(
+      file_data=types.FileData(
+          file_uri="gs://bucket/artifact/0"
+      )
+  )
+  content = types.Content(
+      role="user",
+      parts=[file_part],
+  )
+
+  with caplog.at_level(logging.WARNING, logger="google.adk.models.lite_llm"):
+    await _content_to_message_param(content)
+
+  assert any(
+      "Could not determine MIME type" in record.message
+      for record in caplog.records
+  ), "Expected a warning about MIME type fallback"
+
+
+@pytest.mark.asyncio
+async def test_content_to_message_param_function_response_with_extra_parts_propagates_model():
+  """Test that model parameter is propagated in recursive calls for mixed parts."""
+  tool_part = types.Part.from_function_response(
+      name="load_image",
+      response={"status": "success"},
+  )
+  tool_part.function_response.id = "tool_call_1"
+
+  text_part = types.Part.from_text(text="Here is the result")
+
+  content = types.Content(
+      role="user",
+      parts=[tool_part, text_part],
+  )
+
+  # Call with model parameter — should not raise and should produce valid output
+  messages = await _content_to_message_param(
+      content, provider="anthropic", model="anthropic/claude-4-sonnet"
+  )
+  assert isinstance(messages, list)
+  assert len(messages) == 2
+  # First message is tool response
+  assert messages[0]["role"] == "tool"
+  assert messages[0]["tool_call_id"] == "tool_call_1"
+  # Second message is the text follow-up
+  assert messages[1]["role"] == "user"

From c03864d4565e09bb4f662463e36fe91583bae671 Mon Sep 17 00:00:00 2001
From: Enjoy Kumawat <ekumawat54@gmail.com>
Date: Thu, 9 Apr 2026 13:11:50 +0530
Subject: [PATCH 2/2] style: apply pyink formatting and add return type
 annotations

---
 tests/unittests/models/test_litellm.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tests/unittests/models/test_litellm.py b/tests/unittests/models/test_litellm.py
index 891bf4f984..e92c5d1da3 100644
--- a/tests/unittests/models/test_litellm.py
+++ b/tests/unittests/models/test_litellm.py
@@ -4899,7 +4899,7 @@ async def test_content_to_message_param_anthropic_no_signature_falls_back():
 @pytest.mark.asyncio
 async def test_content_to_message_param_file_uri_mime_fallback_logs_warning(
     caplog,
-):
+) -> None:
   """Test that falling back to application/octet-stream logs a warning."""
   file_part = types.Part(
       file_data=types.FileData(
@@ -4921,7 +4921,7 @@ async def test_content_to_message_param_file_uri_mime_fallback_logs_warning(
 
 
 @pytest.mark.asyncio
-async def test_content_to_message_param_function_response_with_extra_parts_propagates_model():
+async def test_content_to_message_param_function_response_with_extra_parts_propagates_model() -> None:
   """Test that model parameter is propagated in recursive calls for mixed parts."""
   tool_part = types.Part.from_function_response(
       name="load_image",