[BUG] MCP tool streaming output causes scroll jumping/flickering with long conversation context

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?

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Title: MCP tool streaming output causes scroll jumping/flickering with long conversation context

Labels: bug, ui

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Description

When calling MCP tools (specifically codex mcp-server) in a conversation with a long context, the terminal UI experiences severe scroll jumping and content flickering. The scrollbar jumps up and down repeatedly, and the content area becomes unstable.

Environment

• Claude Code version: 2.0.76
• Codex CLI version: 0.77.0
• OS: Windows 10/11
• Terminal: Windows Terminal / PowerShell

MCP Configuration

codex: codex mcp-server - Connected

Steps to Reproduce

1. Start a Claude Code session
2. Have a conversation with multiple exchanges to build up context (e.g., 10+ messages or significant code discussions)
3. Call the codex__codex MCP tool with any prompt
4. Observe the terminal output

Expected Behavior

The Codex output should stream smoothly, with the viewport staying stable or smoothly scrolling to show new content.

Actual Behavior

• The scrollbar jumps up and down erratically
• Content in the terminal flickers and shifts position repeatedly
• The display becomes difficult to read during the MCP tool execution
• The issue worsens as the conversation context grows longer

Possible Cause

The streaming output from MCP tools appears to conflict with the terminal UI's scroll position calculation. When new content is appended, the scroll position is being recalculated repeatedly, causing the jumping behavior.

Workarounds

• Using /compact before calling MCP tools reduces the issue
• Calling codex directly via Bash instead of MCP avoids the problem

What Should Happen?

---
Title: MCP tool streaming output causes scroll jumping/flickering with long conversation context

Labels: bug, ui

---
Description

When calling MCP tools (specifically codex mcp-server) in a conversation with a long context, the terminal UI experiences severe scroll jumping and content flickering. The scrollbar jumps up and down repeatedly, and the content area becomes unstable.

Environment

• Claude Code version: 2.0.76
• Codex CLI version: 0.77.0
• OS: Windows 10/11
• Terminal: Windows Terminal / PowerShell

MCP Configuration

codex: codex mcp-server - Connected

Steps to Reproduce

1. Start a Claude Code session
2. Have a conversation with multiple exchanges to build up context (e.g., 10+ messages or significant code discussions)
3. Call the codex__codex MCP tool with any prompt
4. Observe the terminal output

Expected Behavior

The Codex output should stream smoothly, with the viewport staying stable or smoothly scrolling to show new content.

Actual Behavior

• The scrollbar jumps up and down erratically
• Content in the terminal flickers and shifts position repeatedly
• The display becomes difficult to read during the MCP tool execution
• The issue worsens as the conversation context grows longer

Possible Cause

The streaming output from MCP tools appears to conflict with the terminal UI's scroll position calculation. When new content is appended, the scroll position is being recalculated repeatedly, causing the jumping behavior.

Workarounds

• Using /compact before calling MCP tools reduces the issue
• Calling codex directly via Bash instead of MCP avoids the problem

Error Messages/Logs

Steps to Reproduce

---
Title: MCP tool streaming output causes scroll jumping/flickering with long conversation context

Labels: bug, ui

---
Description

When calling MCP tools (specifically codex mcp-server) in a conversation with a long context, the terminal UI experiences severe scroll jumping and content flickering. The scrollbar jumps up and down repeatedly, and the content area becomes unstable.

Environment

• Claude Code version: 2.0.76
• Codex CLI version: 0.77.0
• OS: Windows 10/11
• Terminal: Windows Terminal / PowerShell

MCP Configuration

codex: codex mcp-server - Connected

Steps to Reproduce

1. Start a Claude Code session
2. Have a conversation with multiple exchanges to build up context (e.g., 10+ messages or significant code discussions)
3. Call the codex__codex MCP tool with any prompt
4. Observe the terminal output

Expected Behavior

The Codex output should stream smoothly, with the viewport staying stable or smoothly scrolling to show new content.

Actual Behavior

• The scrollbar jumps up and down erratically
• Content in the terminal flickers and shifts position repeatedly
• The display becomes difficult to read during the MCP tool execution
• The issue worsens as the conversation context grows longer

Possible Cause

The streaming output from MCP tools appears to conflict with the terminal UI's scroll position calculation. When new content is appended, the scroll position is being recalculated repeatedly, causing the jumping behavior.

Workarounds

• Using /compact before calling MCP tools reduces the issue
• Calling codex directly via Bash instead of MCP avoids the problem

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

last

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_