[BUG] Reply to earlier message wipes all subsequent conversation history from 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?

The "reply" feature is designed to reference a specific point in the conversation. However, when replying to an earlier message, all subsequent conversation history is removed from Claude's context window. This is not the intended behavior — replying should preserve full context, not destroy it.

Steps to reproduce:

Have a working coding session with Claude Code
Scroll up to an earlier message
Click "Reply" on that message and send a new message
Claude loses all memory of everything that happened after that earlier message

Actual behavior:
All messages after the replied-to message are silently removed from Claude's context. Claude has no awareness that this happened. It continues as if it has full context, but is actually missing all code changes, decisions, and progress made after that point. The user may not notice, and Claude cannot flag the issue because it doesn't know what it's missing.

Why this is severe:
Claude may overwrite existing work, re-implement completed features, or give incorrect information about the project state — all while appearing fully confident. The damage to a codebase can be significant before anyone notices.

What Should Happen?

Replying to an earlier message should only serve as a reference point. Claude should retain full context of the entire conversation — nothing should be deleted or truncated.

Error Messages/Logs

Steps to Reproduce

Steps to reproduce:

1. Have a working coding session with Claude Code
2. Scroll up to an earlier message
3. Click "Reply" on that message and send a new message
4. Claude loses all memory of everything that happened after that earlier message

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

1.8555.2

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_