fix: accept Azure assistant file ids

Author: he-yufeng

src/google/adk/models/lite_llm.py

@@ -281,7 +281,7 @@ def _infer_mime_type_from_uri(uri: str) -> Optional[str]:
 
 def _looks_like_openai_file_id(file_uri: str) -> bool:
   """Returns True when file_uri resembles an OpenAI/Azure file id."""
-  return file_uri.startswith("file-")
+  return file_uri.startswith(("file-", "assistant-"))
 
 
 def _is_http_url(uri: str) -> bool:

tests/unittests/models/test_litellm.py

@@ -2943,6 +2943,20 @@ async def test_get_content_file_uri_file_id_required_preserves_file_id(
   assert content == [{"type": "file", "file": {"file_id": "file-abc123"}}]
 
 
+@pytest.mark.asyncio
+async def test_get_content_file_uri_azure_preserves_assistant_file_id():
+  parts = [
+      types.Part(
+          file_data=types.FileData(
+              file_uri="assistant-abc123",
+              mime_type="application/pdf",
+          )
+      )
+  ]
+  content = await _get_content(parts, provider="azure", model="azure/gpt-4.1")
+  assert content == [{"type": "file", "file": {"file_id": "assistant-abc123"}}]
+
+
 @pytest.mark.asyncio
 @pytest.mark.parametrize(
     "provider,model",