[BUG] Agent loses context mid-task when working with moderately-sized documents (~660 lines). Repeated failures across multiple attempts/agents.

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?

What happened: Agent loses context mid-task when working with moderately-sized documents (~660 lines). Repeated failures across multiple attempts/agents.
Reproduction: Ask Claude Code to apply a list of corrections to a ~660 line markdown file. Agent stalls, loses context, or fails to complete the write.
Environment: Claude Opus 4.6 (1M context), VS Code extension, macOS

What Should Happen?

Complete the planning task. I keep getting the message 'Not responding'.

Error Messages/Logs

Steps to Reproduce

The context window shouldn't be an issue for a document this size — this sounds like a bug in how conversation state or tool results are being managed, not an actual token limit problem.

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.17

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_