[BUG] Agent Teams: Teammate cannot exit properly in v2.1.76 (2.1.74 works, 2.1.75 broken)

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Agent Teams: Teammate cannot exit properly in v2.1.76 (works fine in v2.1.74)

The Agent Teams feature has an issue where teammates cannot exit normally in version 2.1.76.
The same operations work correctly in version 2.1.74.

Test prompt as below:

You are the team lead.
Follow the steps below **strictly in order**, do not skip any steps.

## Step 1: Create a team
Use `Teammate spawnTeam` to create a team named "hello-team".

## Step 2: Spawn 3 teammates
Use the `Task` tool to spawn 3 teammates one by one (can be sent in parallel).
The spawn prompts are as follows:

- **teammate-1**:
  "You are teammate-1, one of the team members.
  Wait for a message from the team-lead.
  Upon receiving it, reply to the team-lead using `Teammate write` with the content 'me too'.
  Immediately after replying, wait for `shutdown_request`.
  When you receive it, reply 'approve' and exit.
  Do not do anything else proactively."

- **teammate-2**:
  "You are teammate-2, one of the team members.
  Wait for a message from the team-lead.
  Upon receiving it, reply to the team-lead using `Teammate write` with the content 'me too'.
  Immediately after replying, wait for `shutdown_request`.
  When you receive it, reply 'approve' and exit.
  Do not do anything else proactively."

- **teammate-3**:
  "You are teammate-3, one of the team members.
  Wait for a message from the team-lead.
  Upon receiving it, reply to the team-lead using `Teammate write` with the content 'me too'.
  Immediately after replying, wait for `shutdown_request`.
  When you receive it, reply 'approve' and exit.
  Do not do anything else proactively."

What Should Happen?

The teammate can exit properly.

Error Messages/Logs

Steps to Reproduce

Run the test prompt.

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.76

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_