[BUG] Plan mode outputs full plan to chat on every update

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?

Description

Since plan files started being written to ~/.claude/plans/, Claude outputs the entire plan to chat whenever any part changes.

Before

• Plan updates in chat showed relevant changes
• Easy to follow what changed between iterations

After

• Every plan modification dumps full plan content to chat
• User must manually diff to find what changed
• CLAUDE.md conciseness instructions ignored during plan output
• Claude sometimes enters plan mode for simple questions that don't need planning

Environment

• Claude Code VSCode extension (Cursor)
• Plans written to ~/.claude/plans/

What Should Happen?

• Show only changed sections, or diff markers
• Respect CLAUDE.md instructions for concise output
• Don't enter plan mode for direct questions

Error Messages/Logs

Steps to Reproduce

1. Start a session, enter plan mode
2. Get initial plan
3. Request modification to one section
4. Observe: full plan repeated instead of delta

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.0.55 (Claude Code)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Cursor

Additional Information

_No response_