fix(agent): preserve interrupted tool-call turns

Keep tool-call assistant messages valid across provider sanitization and avoid trailing user-only history after model errors. This prevents follow-up requests from sending broken tool chains back to the gateway.

nanobot/providers/base.py

@@ -375,6 +375,14 @@ class LLMProvider(ABC):
                 and role in ("user", "assistant")
             ):
                 prev = merged[-1]
+                if role == "assistant":
+                    prev_has_tools = bool(prev.get("tool_calls"))
+                    curr_has_tools = bool(msg.get("tool_calls"))
+                    if curr_has_tools:
+                        merged[-1] = dict(msg)
+                        continue
+                    if prev_has_tools:
+                        continue
                 prev_content = prev.get("content") or ""
                 curr_content = msg.get("content") or ""
                 if isinstance(prev_content, str) and isinstance(curr_content, str):

nanobot/providers/openai_compat_provider.py

@@ -243,6 +243,10 @@ class OpenAICompatProvider(LLMProvider):
                     tc_clean["id"] = map_id(tc_clean.get("id"))
                     normalized.append(tc_clean)
                 clean["tool_calls"] = normalized
+                if clean.get("role") == "assistant":
+                    # Some OpenAI-compatible gateways reject assistant messages
+                    # that mix non-empty content with tool_calls.
+                    clean["content"] = None
             if "tool_call_id" in clean and clean["tool_call_id"]:
                 clean["tool_call_id"] = map_id(clean["tool_call_id"])
         return self._enforce_role_alternation(sanitized)