[BUG] Viewport jumps to top on every interaction in browser-based terminal (regression after 2.1.64)

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 using Claude Code in a browser-based SSH terminal (NAS Docker GUI),
the viewport jumps to the top of the page on every interaction — sending
a message, approving a tool use, etc. The user has to manually scroll
back down after each action.

What Should Happen?

The viewport should stay at the bottom (latest content) after every interaction, not jump to the top of the conversation.

Steps to Reproduce

• Environment: Node.js 22 Docker container on NAS
• Terminal: Browser-based SSH terminal (NAS Docker management GUI, likely

xterm.js)

• Access method: docker exec -it or NAS web terminal

Version info

• 2.1.64: No jumping, works correctly
• 2.1.81: Jumps briefly then auto-corrects back
• 2.1.90: Jumps and stays at top, must manually scroll down

## What was tried

• Custom terminfo disabling alternate screen buffer (smcup/rmcup) — didn't

help

• tmux with mouse on — masked the issue but introduced mouse/copy conflicts
• dtach — transparent passthrough, jumping still occurs
• Downgrading to 2.1.64 — fully resolves the issue

Claude Model

us.anthropic.claude-opus-4-6-v1

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.90

Platform

AWS Bedrock

Operating System

Other Linux

Terminal/Shell

Other

Additional Information