background-agent-pings

指导后台 agent 用系统提醒作为进度通知，避免轮询。

把系统提醒当作后台 agent 的进度通知，不用不停轮询。启动后台任务后可以继续做其他事，系统会以提醒告知 agent 的进展、使用新工具或何时在指定路径写出文件。适合需要并行执行和监控的场景，能降低轮询开销并保持清晰的进度追踪。

# Background Agent Pings

Trust system reminders as agent progress notifications. Don't poll.

## Pattern

When you launch a background agent, **continue working on other tasks**. The system will notify you via reminders when:
- Agent makes progress: `Agent <id> progress: X new tools used, Y new tokens`
- Agent writes output file (check the path you specified)

## DO

```
1. Task(run_in_background=true, prompt="... Output to: .claude/cache/agents/<type>/output.md")
2. Continue with next task immediately
3. When system reminder shows agent activity, check if output file exists
4. Read output file only when agent signals completion
```

## DON'T

```
# BAD: Polling wastes tokens and time
Task(