Fix assistant messages without tool calls not being saved to session

nanobot/agent/loop.py

@@ -225,7 +225,16 @@ class AgentLoop:
                         messages, tool_call.id, tool_call.name, result
                     )
             else:
-                final_content = self._strip_think(response.content)
+                clean = self._strip_think(response.content)
+                if on_progress and clean:
+                    await on_progress(clean)
+                messages = self.context.add_assistant_message(
+                    messages,
+                    clean,
+                    tool_calls=None,
+                    reasoning_content=response.reasoning_content,
+                )
+                final_content = clean
                 break
 
         if final_content is None and iteration >= self.max_iterations: