[BUG] Terminal scroll shows duplicated prompt/response on session start with parallel tool calls

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?

On session start, when Claude makes multiple parallel tool calls (MCP calls,
agent spawns), the terminal scroll buffer shows the user's initial prompt
and Claude's response duplicated multiple times. Scrolling up reveals the
same prompt/response pair rendered 2-3+ times.

What Should Happen?

## Expected Behavior

User prompt and Claude response appear once in the scroll buffer.

Error Messages/Logs

Steps to Reproduce

1. Start a new Claude Code session with multiple MCP servers connected

(Gmail, Google Calendar, WealthBox, etc.) and a SessionStart hook triggering
automated workflows

1. Send a short initial message (e.g. "gm")

calendar pull, 5+ email reads, 2 agent spawns)

1. Scroll up in the terminal

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.101

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

Expected Behavior

User prompt and Claude response appear once in the scroll buffer.

## Actual Behavior

User prompt and Claude response appear duplicated multiple times.

## Environment

• Claude Code version: 2.1.101
• OS: macOS (Darwin 23.6.0)
• Model: claude-opus-4-6 (1M context)
• MCP servers: 8+ (Google Workspace, Gmail, Calendar, WealthBox, Knowledge

Graph, others)

• Session: Heavy parallel tool use on startup — 3 simultaneous Gmail

searches, 5 email reads, 2 agent spawns

## Notes

This is a rendering/display issue only. Claude's responses are correct and
not duplicated in behavior — the scroll buffer just shows them multiple
times visually.