[BUG] Multiple issues in new version, working in CLI v2.1.156

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?

Title: Multiple subagents edit the same file concurrently, causing write collisions

Description
When multiple subagents are active, two or more attempt to modify the same file
at the same time, producing write-collision errors.

Title: Custom subagent ("art-director") invoked 3x instead of once, ~1.1M tokens consumed

Description
A custom "art-director" profile/subagent was called three times in a single
task where it should have run once, consuming roughly 1.1M tokens.

Title: Brainstorming question menu returns to already-answered questions

Description
During an interactive brainstorming flow, the question menu repeatedly returns
to questions that were already answered. This happened 3x today.

Impact
Edits fail; work has to be retried, and partial writes risk leaving the file
in an inconsistent state. Extra tokens burned. Time wasted. Developer annoyed.

Environment

• OS: Windows 10

What Should Happen?

Maybe test in a real production environment before pushing?

Error Messages/Logs

Steps to Reproduce

Steps to reproduce

1. Do any work that involves subagents

Steps to reproduce

1. Do any work that involves subagents

Steps to reproduce

1. Start the brainstorming question flow [name the command/mode if you know it]
2. Answer several questions in sequence
3. Observe the menu re-present previously answered questions

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

v2.1.156

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Other

Additional Information

_No response_