feat(cron): improve cron job context handling

Improve cron job execution context to ensure proper message delivery and
session history recording.

Changes:
- Add [绯荤粺瀹氭椂浠诲姟] prefix to cron reminder messages to clearly mark
  them as system-driven, not user queries
- Use user role for cron reminder messages (required by some LLM APIs)
- Properly handle MessageTool to avoid duplicate message delivery
- Correctly save turn history with proper skip count
- Ensure Runtime Context is included in the message list

This ensures that:
1. Cron jobs execute with proper context
2. Messages are correctly delivered to users
3. Session history accurately records cron job interactions
4. The LLM understands these are system-driven reminders, not user queries

nanobot/cli/commands.py

@@ -295,20 +295,55 @@ def gateway(
     # Set cron callback (needs agent)
     async def on_cron_job(job: CronJob) -> str | None:
         """Execute a cron job through the agent."""
-        response = await agent.process_direct(
-            job.payload.message,
-            session_key=f"cron:{job.id}",
-            channel=job.payload.channel or "cli",
-            chat_id=job.payload.to or "direct",
+        from nanobot.agent.tools.message import MessageTool
+        
+        cron_session_key = f"cron:{job.id}"
+        cron_session = agent.sessions.get_or_create(cron_session_key)
+        
+        reminder_note = (
+            f"[系统定时任务] ⏰ 计时已结束\n\n"
+            f"定时任务 '{job.name}' 已触发。定时内容：{job.payload.message}\n\n"
         )
-        if job.payload.deliver and job.payload.to:
+        
+        cron_session.add_message(role="user", content=reminder_note)
+        agent.sessions.save(cron_session)
+        
+        agent._set_tool_context(
+            job.payload.channel or "cli",
+            job.payload.to or "direct",
+            None
+        )
+        
+        message_tool = agent.tools.get("message")
+        if isinstance(message_tool, MessageTool):
+            message_tool.start_turn()
+        
+        history = cron_session.get_history(max_messages=agent.memory_window)
+        
+        messages = [
+            {"role": "system", "content": agent.context.build_system_prompt()},
+            *history,
+            {"role": "user", "content": agent.context._build_runtime_context(
+                job.payload.channel or "cli",
+                job.payload.to or "direct"
+            )},
+        ]
+        
+        final_content, _, all_msgs = await agent._run_agent_loop(messages)
+        agent._save_turn(cron_session, all_msgs, 1 + len(history) + 1)
+        agent.sessions.save(cron_session)
+        
+        if isinstance(message_tool, MessageTool) and message_tool._sent_in_turn:
+            return final_content
+        
+        if job.payload.deliver and job.payload.to and final_content:
             from nanobot.bus.events import OutboundMessage
             await bus.publish_outbound(OutboundMessage(
                 channel=job.payload.channel or "cli",
                 chat_id=job.payload.to,
-                content=response or ""
+                content=final_content
             ))
-        return response
+        return final_content
     cron.on_job = on_cron_job
 
     # Create channel manager