ExitPlanMode tool fails silently — nothing displayed to user

Bug Report

Description

When Claude calls ExitPlanMode in plan mode, the tool returns success on Claude's side but nothing is displayed to the user. The user sees no plan content at all.

Steps to Reproduce

1. User asks Claude to plan a feature implementation
2. Claude enters plan mode via EnterPlanMode
3. Claude writes a plan to the plan file
4. Claude calls ExitPlanMode
5. Expected: User sees the plan and can approve/reject
6. Actual: Nothing displays. User sees no output.

Impact

Claude keeps re-calling ExitPlanMode because it appears to succeed, while the user sees nothing. In this session, the tool was called 10+ times with the user repeatedly telling Claude it wasn't working, but Claude kept doing the same thing because it received no error signal.

Environment

• Model: Claude Opus 4.6
• Platform: macOS (Darwin 25.3.0)
• Shell: fish

Additional Context

The user had to explicitly ask Claude to stop calling the tool and paste the plan as plain text instead. The lack of error feedback from the tool made it impossible for Claude to self-correct.