[BUG] Main composer doesn't scroll with cursor position — content above visible window becomes inaccessible while typing long prompts

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?

The main prompt composer has a max height, which is expected and necessary to preserve space for the conversation view. However, when the input grows beyond that height, there's no visible scrolling tied to cursor position. Once you keep typing past the visible window, the beginning of your prompt (or wherever the cursor currently isn't) becomes inaccessible for reading, reviewing, or verifying — you're effectively typing blind above a certain length, with no way to scroll up within the composer to check what you've already written.

This is distinct from #12875 (the "Type here to tell Claude what to do differently" permission mini-field), which was closed as "Not planned" because that field is intentionally scoped for short feedback, with the composer suggested as the fallback for longer input. This issue is specifically about that fallback — the main composer — not having a working scroll behavior either.

What Should Happen?

The composer should scroll vertically based on cursor position, the way terminal editors (vim, nano, readline multi-line mode) handle buffers larger than the visible viewport: the line containing the cursor should always stay within the visible window, and the max height constraint on the composer itself stays unchanged. Eventually, this height could be increased, but that would mean choosing between the visibility of the command prompt and that of the history. With a status bar and a task list, for example, the display is already vertically crowded.

Error Messages/Logs

Steps to Reproduce

1. Open Claude Code in the terminal.
2. Start typing a prompt long enough to exceed the composer's max visible height.
3. Continue typing past that point,.
4. Observe that the portion of the text above the currently visible window cannot be scrolled into view — there's no cursor-following scroll.

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

v2.1.278

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Other

Additional Information

Related to #12875, but scoped to the main composer rather than the permission-prompt mini-field, which was closed as not-planned with the composer explicitly recommended as the place for longer input — making this the remaining gap. The composer resets after sending, so raising its effective editable height (or at minimum adding cursor-following scroll) wouldn't cost permanent conversation-view space.

NB : I use Ghostty 1.3.1