[Bug] tengu_pewter_brook: True GrowthBook flag enables mouse reporting, breaking copy/paste in SSH terminals

Summary

When tengu_pewter_brook is set to True in ~/.claude.json (via GrowthBook A/B test),
Claude Code enables mouse reporting (ESC[?1000h) after login, breaking copy/paste in SSH terminals.

Environment

• OS: Linux (WSL2 + Docker container)
• Terminal: MobaXterm (SSH)
• Claude Code versions affected: 2.1.143 ~ 2.1.152 (all tested)

Symptoms

After /login and TUI startup:

• Cursor changes from I-beam to arrow (mouse reporting active)
• Right-click no longer shows terminal context menu
• Text selection via mouse drag stops working

Before /login: everything works normally.

Root Cause

~/.claude.json → cachedGrowthBookFeatures → tengu_pewter_brook: true

Reproduction

1. Ensure ~/.claude.json has cachedGrowthBookFeatures.tengu_pewter_brook = true
2. Start claude in an SSH terminal (MobaXterm)
3. Run /login
4. After login succeeds, cursor changes to arrow and right-click no longer works

Workaround

Edit ~/.claude.json and set tengu_pewter_brook: false, then restart Claude Code.
Toggling only this single flag (all others unchanged) fixes the issue immediately.

Notes

• Kiro does not exhibit this behavior (does not enable mouse reporting)
• TERM=rxvt, CI=true, pre-launch ESC reset do NOT fix it
• Flag was pushed to some accounts around 2026-05-26