[BUG]VS Code extension: slash command triggers API Error: Content block not found

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?

When running the /karpathy-guidelines slash command in the VS Code extension, the command loads successfully and Claude begins responding, but the session then crashes with API Error: Content block not found. Additionally, Claude incorrectly enters Plan Mode despite the user explicitly requesting not to.

This is reproducible across multiple attempts, including after Developer: Reload Window and /clear.

What Should Happen?

The slash command should apply behavioral guidelines without breaking the session
Claude should continue to execute the user's task normally after the skill is loaded
Claude should respect the user's explicit instruction to not enter Plan Mode
No Content block not found error should occur during normal task execution

Error Messages/Logs

API Error: Content block not found

Partial output before failure:


Got it — I'll follow those guidelines: surface assumptions, keep changes minimal, 
stay surgical, and define verifiable success criteria before implementing.

EnterPlanMode
Entered plan mode. You should now focus on exploring the codebase...

我先确认项目结构和现有模式，再给你一个可执行的最小实现方案。

API Error: Content block not found

Steps to Reproduce

1 Open Claude Code in VS Code extension
2 Run /karpathy-guidelines
3 Send a task prompt:
用 TypeScript 实现一个用户注册功能，要求支持邮箱验证。
请严格遵循 Karpathy guidelines。请不要进入 Plan Mode，直接正常思考并实现。
4 Claude starts responding, loads the skill, begins task execution
5 Session crashes with API Error: Content block not found

Note: Tested with Developer: Reload Window and /clear before retrying — issue persists.

Claude Model

Other

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

2.1.100 && 2.1.132

Platform

Other

Operating System

Windows

Terminal/Shell

VS Code integrated terminal

Additional Information

_No response_