fix(provider): backfill DeepSeek reasoning_content instead of dropping history (#3554, #3584)

tests/providers/test_litellm_kwargs.py

@@ -620,7 +620,8 @@ def _tool_call(call_id: str) -> dict:
     }
 
 
-def test_deepseek_thinking_drops_tool_history_missing_reasoning_content() -> None:
+def test_deepseek_thinking_backfills_missing_reasoning_content_on_tool_history() -> None:
+    """Backfill reasoning_content="" instead of dropping the turn (#3554, #3584)."""
     kwargs = _deepseek_kwargs([
         {"role": "system", "content": "system"},
         {"role": "user", "content": "can we use wechat?"},
@@ -629,10 +630,12 @@ def test_deepseek_thinking_drops_tool_history_missing_reasoning_content() -> Non
         {"role": "user", "content": "continue"},
     ])
 
-    assert kwargs["messages"] == [
-        {"role": "system", "content": "system"},
-        {"role": "user", "content": "continue"},
+    assert [m["role"] for m in kwargs["messages"]] == [
+        "system", "user", "assistant", "tool", "user",
     ]
+    assistant = kwargs["messages"][2]
+    assert assistant["reasoning_content"] == ""
+    assert assistant["tool_calls"][0]["function"]["name"] == "my"
 
 
 def test_deepseek_thinking_keeps_tool_history_with_reasoning_content() -> None:
@@ -654,20 +657,6 @@ def test_deepseek_thinking_keeps_tool_history_with_reasoning_content() -> None:
     assert kwargs["messages"][2]["role"] == "tool"
 
 
-def test_deepseek_thinking_drops_current_bad_tool_turn_without_followup_user() -> None:
-    kwargs = _deepseek_kwargs([
-        {"role": "system", "content": "system"},
-        {"role": "user", "content": "can we use wechat?"},
-        {"role": "assistant", "content": "", "tool_calls": [_tool_call("call_bad")]},
-        {"role": "tool", "tool_call_id": "call_bad", "name": "my", "content": "channels"},
-    ])
-
-    assert kwargs["messages"] == [
-        {"role": "system", "content": "system"},
-        {"role": "user", "content": "can we use wechat?"},
-    ]
-
-
 def test_openai_compat_keeps_tool_calls_after_consecutive_assistant_messages() -> None:
     with patch("nanobot.providers.openai_compat_provider.AsyncOpenAI"):
         provider = OpenAICompatProvider()
@@ -937,8 +926,8 @@ def test_backfill_does_not_touch_messages_when_thinking_explicitly_off() -> None
                 assert "reasoning_content" not in msg
 
 
-def test_deepseek_v4_drops_incomplete_reasoning_history_when_effort_implicit() -> None:
-    """DeepSeek-V4 may default to thinking, so incomplete legacy history is trimmed."""
+def test_deepseek_v4_backfills_incomplete_reasoning_history_when_effort_implicit() -> None:
+    """DeepSeek-V4 reasons natively: backfill even without explicit reasoning_effort."""
     spec = find_by_name("deepseek")
     with patch("nanobot.providers.openai_compat_provider.AsyncOpenAI"):
         p = OpenAICompatProvider(api_key="k", default_model="deepseek-v4-pro", spec=spec)
@@ -958,12 +947,16 @@ def test_deepseek_v4_drops_incomplete_reasoning_history_when_effort_implicit() -
         reasoning_effort=None, tool_choice=None,
     )
 
-    assert [msg["role"] for msg in kw["messages"]] == ["system", "user"]
+    assert [msg["role"] for msg in kw["messages"]] == [
+        "system", "user", "assistant", "tool", "user",
+    ]
+    assert kw["messages"][2]["reasoning_content"] == ""
     assert kw["messages"][-1]["content"] == "thanks"
 
 
 def test_deepseek_chat_keeps_tool_history_when_effort_implicit() -> None:
-    """Implicit cleanup must not trim non-thinking DeepSeek chat models."""
+    """Non-thinking deepseek-chat must keep history untouched and must NOT
+    receive backfilled reasoning_content (#3554, #3584)."""
     spec = find_by_name("deepseek")
     with patch("nanobot.providers.openai_compat_provider.AsyncOpenAI"):
         p = OpenAICompatProvider(api_key="k", default_model="deepseek-chat", spec=spec)
@@ -985,6 +978,7 @@ def test_deepseek_chat_keeps_tool_history_when_effort_implicit() -> None:
     roles = [msg["role"] for msg in kw["messages"]]
     assert roles == ["user", "assistant", "tool", "user"]
     assert kw["messages"][1]["tool_calls"]
+    assert "reasoning_content" not in kw["messages"][1]
 
 
 def test_deepseek_coerces_list_content_to_string() -> None: