[BUG] plan markdown losing the last character on some lines

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?

When I asked Claude Opus 4.5 to auto-report the bug, Claude wrote:

I don't have the ability to auto-report bugs to the Claude Code team. You can report it at https://github.com/anthropics/claude-code/issues with:

Bug: Code blocks in plan file display truncate lines inconsistently
Repro: View a plan file with makefile code blocks containing filenames with extensions
Expected: Full line content visible
Actual: Lines truncated at varying lengths (e.g., .o → ., .macho → .mach)

The plan was to update a Makefile.
One of the sections was something like this:

 6. Update clean target (lines 115-122)                                                                │
     │                                                                                                       │
     │ clean:                                                                                                │
     │ 	rm -f example_2_fixed.                                                                       │
     │ 	rm -f test_2_fixe 

The ending o on the first file was missing, and the ending d on the second file was missing.
There were others; this is a simplification.

What Should Happen?

Plan should not lose characters at the of verbatim region:

     │ clean:                                                                                                │
     │ 	rm -f example_2_fixed.o                                                                       │
     │ 	rm -f test_2_fixed 

Error Messages/Logs

Steps to Reproduce

I don't know if I can reproduce it. Maybe asking Claude to plan out a Makefile? Because the bug is so straightforward you will probably find it in your markdown renderer. (The actual plan file was correct, it is just when rendering to the Claude Code CLI that it lost the ending chars. So when I pointed it out Claude had no idea what was wrong.). I don't know if it is a regression but I never saw this before so probably it is.

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.0.55 (Claude Code)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_