test(models): repair anthropic fallback regression assertions

Move the non-standard FunctionResponse assertions back into the regression test that exercises the fallback serialization path, and keep the PDF document test focused on document serialization only.

Validated with pyink --check, the full anthropic_llm test file, and a runtime proof script covering both the fallback tool_result path and the PDF document path.

Author: giulio-leone

tests/unittests/models/test_anthropic_llm.py

@@ -764,27 +764,28 @@ def test_part_to_message_block_with_non_standard_response():
   )
   part.function_response.id = "test_skill_id"
 
-
-def test_part_to_message_block_with_pdf_document():
-  """Test that part_to_message_block handles PDF document parts."""
-  pdf_data = b"%PDF-1.4 fake pdf content"
-  part = Part(
-      inline_data=types.Blob(mime_type="application/pdf", data=pdf_data)
-  )
-
   result = part_to_message_block(part)
 
   assert isinstance(result, dict)
   assert result["tool_use_id"] == "test_skill_id"
   assert result["type"] == "tool_result"
   assert not result["is_error"]
-  # Content must be non-empty and contain the original data
   parsed = json.loads(result["content"])
   assert parsed["skill_name"] == "search_docs"
   assert parsed["instructions"] == "Use the search API to find documents."
   assert parsed["frontmatter"] == {"version": "1.0"}
 
 
+def test_part_to_message_block_with_pdf_document():
+  """Test that part_to_message_block handles PDF document parts."""
+  pdf_data = b"%PDF-1.4 fake pdf content"
+  part = Part(
+      inline_data=types.Blob(mime_type="application/pdf", data=pdf_data)
+  )
+
+  result = part_to_message_block(part)
+
+  assert isinstance(result, dict)
   assert result["type"] == "document"
   assert result["source"]["type"] == "base64"
   assert result["source"]["media_type"] == "application/pdf"