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

nanobot/providers/openai_compat_provider.py

@@ -449,59 +449,6 @@ class OpenAICompatProvider(LLMProvider):
                 clean["content"] = self._coerce_content_to_string(clean.get("content"))
         return self._enforce_role_alternation(sanitized)
 
-    def _drop_deepseek_incomplete_reasoning_history(
-        self,
-        messages: list[dict[str, Any]],
-        model_name: str,
-        reasoning_effort: str | None,
-    ) -> list[dict[str, Any]]:
-        if (
-            not self._spec
-            or self._spec.name != "deepseek"
-        ):
-            return messages
-
-        semantic_effort = reasoning_effort.lower() if isinstance(reasoning_effort, str) else None
-        if semantic_effort in {"none", "minimal", "minimum"}:
-            return messages
-
-        # DeepSeek-V4 can require reasoning_content even when the config did
-        # not explicitly request reasoning_effort. Keep that implicit-thinking
-        # cleanup scoped to known thinking-capable DeepSeek models so normal
-        # deepseek-chat history is not trimmed.
-        if semantic_effort is None:
-            model_lower = model_name.lower()
-            if not any(token in model_lower for token in ("deepseek-v4", "deepseek-reasoner")):
-                return messages
-
-        bad_idx = None
-        for idx, msg in enumerate(messages):
-            if (
-                msg.get("role") == "assistant"
-                and msg.get("tool_calls")
-                and not msg.get("reasoning_content")
-            ):
-                bad_idx = idx
-        if bad_idx is None:
-            return messages
-
-        keep_from = None
-        for idx in range(bad_idx + 1, len(messages)):
-            if messages[idx].get("role") == "user":
-                keep_from = idx
-                break
-
-        if keep_from is None:
-            trimmed = messages[:bad_idx]
-        else:
-            prefix = [msg for msg in messages[:keep_from] if msg.get("role") == "system"]
-            trimmed = prefix + messages[keep_from:]
-        logger.warning(
-            "Dropped {} DeepSeek thinking history message(s) with incomplete reasoning_content",
-            len(messages) - len(trimmed),
-        )
-        return trimmed
-
     # ------------------------------------------------------------------
     # Build kwargs
     # ------------------------------------------------------------------
@@ -542,11 +489,6 @@ class OpenAICompatProvider(LLMProvider):
         if spec and spec.strip_model_prefix:
             model_name = model_name.split("/")[-1]
 
-        messages = self._drop_deepseek_incomplete_reasoning_history(
-            messages,
-            model_name,
-            reasoning_effort,
-        )
         kwargs: dict[str, Any] = {
             "model": model_name,
             "messages": self._sanitize_messages(self._sanitize_empty_content(messages)),
@@ -611,22 +553,22 @@ class OpenAICompatProvider(LLMProvider):
             kwargs["tools"] = tools
             kwargs["tool_choice"] = tool_choice or "auto"
 
-        # Backfill reasoning_content on legacy assistant messages.
-        # DeepSeek V4 (and potentially others) rejects thinking-mode
-        # requests that contain assistant messages without reasoning_content
-        # — even on turns that had no tool calls. This happens when a
-        # session was started with a non-thinking model or without
-        # reasoning_effort, then the user switches thinking mode on
-        # mid-session. Injecting an empty string satisfies the API
-        # without altering semantics (the model treats it as "no
-        # thinking happened on that turn").
-        thinking_active = (
-            (spec and spec.thinking_style and reasoning_effort is not None
-             and semantic_effort not in ("none", "minimal"))
-            or (reasoning_effort is not None and _is_kimi_thinking_model(model_name)
-                and semantic_effort not in ("none", "minimal"))
+        # Backfill reasoning_content="" on assistants missing it: DeepSeek
+        # thinking mode rejects history otherwise (#3554, #3584); "" reads
+        # as "no thinking that turn". DeepSeek-V4/reasoner reason natively,
+        # so backfill even without explicit reasoning_effort.
+        explicit_thinking = (
+            reasoning_effort is not None
+            and semantic_effort not in ("none", "minimal")
+            and ((spec and spec.thinking_style) or _is_kimi_thinking_model(model_name))
         )
-        if thinking_active:
+        implicit_deepseek_thinking = (
+            spec is not None
+            and spec.name == "deepseek"
+            and semantic_effort not in ("none", "minimal", "minimum")
+            and any(t in model_name.lower() for t in ("deepseek-v4", "deepseek-reasoner"))
+        )
+        if explicit_thinking or implicit_deepseek_thinking:
             for msg in kwargs["messages"]:
                 if msg.get("role") == "assistant" and "reasoning_content" not in msg:
                     msg["reasoning_content"] = ""