[BUG] Mac Terminal goes into stroboscopic spasms

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?

I find that my terminal occasionally goes into a crazy scrolling mode where it's impossible to tell whether it's _doing_ something (and I'm just too slow to see what it's doing) or just spasming, but I managed to repro just now when simply attempting to examine the background tasks I had running. Here is a recording of what happened when I pressed the down arrow at the input prompt and hit Enter on "2 background tasks" to view the running tasks.

https://github.com/user-attachments/assets/e46badb4-cf88-45bf-a670-fce3acf68713

I kept the recording mercifully short to avoid creating a huge video file, but in the past, I have watched this for several minutes before realizing that the only useful action is probably to hit Esc and ask the bot what it's doing.

What Should Happen?

The terminal display should display what it's supposed to.

Error Messages/Logs

It looks vaguely like it's scrolling to different points in the scrollback buffer or perhaps channeling an MTV music video from some psychotic rap band in the 1990s.

Steps to Reproduce

This seems to happen completely at random. I can vaguely estimate 2-3 times per week but there seems to be no specific trigger.

Beginning to type a slash command seems to often trigger a milder form of this. Just now when I typed /model because this dialog told me to, it spasmed again, though in this case it's more obvious that it's just a glitch (I think it's switching rapidly between 2 or 3 different positions in the scroll buffer, or perhaps independent screens with different portions of my previous dialogue with it.)

Claude Model

Sonnet (default)

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.5 (Claude Code)

Platform

AWS Bedrock

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

I don't think this is specific to the model or the platform; I had this at home on a different computer where I was using Opus, using the regular Anthropic platform rather than AWS Bedrock.