[BUG] Sticky scroll re-pins to bottom during parallel agent output, making it unreadable

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?

Summary

With several subagents running in parallel, the viewport is re-pinned to the bottom on every agent emit. Scrolling up does not hold — the next emit (often <1s later) yanks the view back down, so it's effectively impossible to read output while agents are running.

Environment

• Claude Code: 2.1.231
• OS: Windows 11 Enterprise (10.0.26200)
• Terminal: VS Code Insiders integrated terminal (VS Code Insiders 1.132.0-insider, PowerShell 7.3.4 Core)
• Install: bundled native binary from the VS Code extension (anthropic.claude-code-2.1.231-win32-x64/resources/native-binary/claude.exe), invoked via a .cmd shim
• TUI renderer: default (no tui key set in settings.json)

What Should Happen?

Steps to reproduce

1. Start a task that spawns several subagents running concurrently. In my case the session had 7 concurrent child processes.
2. While they are emitting output, scroll up to read an earlier result.
3. Wait for any agent to emit.

Expected

Scrolling up disengages tail-follow. The viewport holds position until I explicitly return to the bottom — the standard behavior in less +F, tail -f in a scrollback-capable terminal, and browser devtools consoles. Ideally with a "paused / N new lines below" affordance so the state is visible.

Actual

The viewport is re-pinned to the bottom on the next emit. With 7 agents interleaving this happens multiple times per second, leaving well under a second to read before being scrolled away.

Error Messages/Logs

None, just a bad UE.

Steps to Reproduce

1. Start a task that spawns several subagents running concurrently. In my case the session had 7 concurrent child processes.
2. While they are emitting output, scroll up to read an earlier result.
3. Wait for any agent to emit.

Claude Model

Other

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.231

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

2.1.231