When agent spawns parallel (sub)agents, they report <systemnotification> with 'completed' state directly after launching

### Describe the bug

using Copilot CLI in Mac OS Terminal i notice since v1.0.5 that launching backgroundagents / subagents doesn't work anymore: imidiately after they kick-off: they report completed. Which confuses the orchestrating agent i use and burns a hole in my premiumrequests...

### Affected version

GitHub Copilot CLI 1.0.9

### Steps to reproduce the behavior

1. insruct the agent to perform tasks in parallel
2. as soon as the agent start parallel agents, they report completion imidiately (i see appearing. This makes the 'main' agent think: "ah subagents are done". Then the confusion starts: the agent looks at results, sees none (or partial) results, spawns the parallel agents again, and again, confusion all-over.

### Expected behavior

No premature , parallel agents should report completion when they **actually** complete their tasks, not imidiately after they start.

### Additional context

- Latest Mac OS version
- Mac OS Terminal (zsh)
- Copilot CLI v1.0.9 (problem started from v1.0.5)