fix(deepseek): forward image content in role=tool messages

DeepSeekChatConfig._is_vision_forwardable_content() rejected every
non-user role, so a role=tool message carrying image_url blocks was
silently string-collapsed before the request left LiteLLM — agent
loops that screenshot inside a tool sent pixels that never reached the
model. The DeepSeek Chat Completions API itself accepts and reads
tool-result images (verified directly against the API, issue #44211).

Allow role=tool alongside role=user in the forwardable check; the
model capability gate (supports_vision) still lives in the caller.

litellm/llms/deepseek/chat/transformation.py

@@ -160,13 +160,18 @@ class DeepSeekChatConfig(OpenAIGPTConfig):
 
     def _is_vision_forwardable_content(self, message: AllMessageValues, content: Sequence[object]) -> bool:
         """
-        True only for a user message whose content list holds well-formed
-        text and image_url blocks with at least one image; a block missing
-        its payload falls back to the string collapse instead of crashing
-        or reaching the wire malformed. The model capability gate lives in
-        the caller.
+        True only for a user or tool message whose content list holds
+        well-formed text and image_url blocks with at least one image; a block
+        missing its payload falls back to the string collapse instead of
+        crashing or reaching the wire malformed. The model capability gate
+        lives in the caller.
+
+        ``role="tool"`` is forwardable: the DeepSeek Chat Completions API
+        accepts and reads image_url blocks in tool results (verified directly
+        against the API; bug #44211) — agent loops that screenshot inside a
+        tool rely on it.
         """
-        if message.get("role") != "user":
+        if message.get("role") not in ("user", "tool"):
             return False
         if not all(self._is_forwardable_block(block) for block in content):
             return False

tests/unit/llms/deepseek/test_deepseek_vision_tool_message.py

@@ -0,0 +1,67 @@
+"""
+Tests for DeepSeek vision-content forwarding in role=tool messages.
+
+Bug #44211: ``_is_vision_forwardable_content`` rejected every non-user role,
+so a ``role=tool`` message carrying image_url blocks was silently collapsed
+to text before the request left LiteLLM — while the DeepSeek API itself
+accepts and reads tool-result images.
+"""
+
+import pytest
+
+from litellm.llms.deepseek.chat.transformation import DeepSeekChatConfig
+
+
+TOOL_MESSAGE_WITH_IMAGE = {
+    "role": "tool",
+    "tool_call_id": "abc",
+    "content": [
+        {"type": "text", "text": "screenshot:"},
+        {"type": "image_url", "image_url": {"url": "data:image/png;base64,aGVsbG8="}},
+    ],
+}
+
+
+class TestVisionForwardableContent:
+    def test_tool_message_with_image_is_forwardable(self):
+        config = DeepSeekChatConfig()
+        assert config._is_vision_forwardable_content(
+            message=TOOL_MESSAGE_WITH_IMAGE,
+            content=TOOL_MESSAGE_WITH_IMAGE["content"],
+        )
+
+    def test_user_message_with_image_stays_forwardable(self):
+        config = DeepSeekChatConfig()
+        message = {"role": "user", "content": TOOL_MESSAGE_WITH_IMAGE["content"]}
+        assert config._is_vision_forwardable_content(message=message, content=message["content"])
+
+    def test_assistant_message_stays_collapsed(self):
+        config = DeepSeekChatConfig()
+        message = {"role": "assistant", "content": TOOL_MESSAGE_WITH_IMAGE["content"]}
+        assert not config._is_vision_forwardable_content(message=message, content=message["content"])
+
+    def test_image_missing_payload_falls_back(self):
+        config = DeepSeekChatConfig()
+        message = {
+            "role": "tool",
+            "content": [
+                {"type": "text", "text": "screenshot:"},
+                {"type": "image_url", "image_url": {"url": ""}},
+            ],
+        }
+        assert not config._is_vision_forwardable_content(message=message, content=message["content"])
+
+
+class TestForwardOrCollapseContent:
+    def test_tool_message_image_content_is_not_collapsed(self):
+        config = DeepSeekChatConfig()
+        out = config._forward_or_collapse_content(message=TOOL_MESSAGE_WITH_IMAGE, forward_images=True)
+        assert isinstance(out.get("content"), list)
+        blocks = out["content"]
+        assert any(isinstance(block, dict) and block.get("type") == "image_url" for block in blocks)
+
+    def test_tool_message_text_only_still_collapsed(self):
+        config = DeepSeekChatConfig()
+        message = {"role": "tool", "content": [{"type": "text", "text": "plain"}]}
+        out = config._forward_or_collapse_content(message=message, forward_images=True)
+        assert out.get("content") == "plain"