[BUG] backticks and exclamations in a slash command trigger permission check

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?

• I have a custom slash command which takes one argument
• the slash command does not involve bash
• but it causes Claude Code to throw Error: Bash command permission check failed for pattern and then a huge blob of markdown is the "pattern"
• It broke starting with Claude Code 1.0.54 (worked in 1.0.53)
• changelog for 1.0.54 says "Custom slash commands: Added argument-hint to frontmatter"
• superficially similar (red herring) to #3662
• very similar to #6660

What Should Happen?

• it should run the slash command (like it did in 1.0.53)

Error Messages/Logs

Steps to Reproduce

The exact slash command which causes the issue is https://github.com/diffplug/gitcasso/blob/f8b5faa2b3e9c4295858f5e2b6e079eda2b05fa2/.claude/commands/corpus-loop.md?plain=1

Key excerpts:

---
argument-hint: [corpus_slug]
description: uses Playwright MCP and the `corpus` to parse page elements
---

- using Playwright MCP, navigate to `http://localhost:3001/corpus/$1/gitcasso`
- the page will have a div with id `gitcasso-comment-spots`, wait 500ms for it to settle

(blah blah blah)

- Don't hedge your bets and write lots of fallback code or strings of `?.`. Have a specific piece of data you want to get, use non-null `!` assertions where necessary to be clear about getting.
- If a field is empty, represent it with an empty string. Don't use placeholders when extracting data.
- The pages we are scraping are going to change over time, and it's easier to fix broken ones if we know exactly what used to work. If the code has lots of branching paths, it's harder to tell what it was doing.

## Troubleshooting

- If you see `"spot": "NO_SPOT"` but expect an enhancer to match:
  - Check console logs for enhancer attempts (e.g., `"eE examing url"`)
  - Look for specific rejection reasons in the enhancer's `tryToEnhance` method

For an exact reproducer

• clone https://github.com/diffplug/gitcasso
• run claude
• /corpus-loop gh_issue_edit_multiple
• you'll get this error message:

> /corpus-loop slug
  ⎿ Error: Bash command permission check failed for pattern "!` assertions where necessary to be clear about getting.
    - If a field is empty, represent it with an empty string. Don't use placeholders when extracting data.
    - The pages we are scraping are going to change over time, and it's easier to fix broken ones if we know exactly what used to work. If the
     code has lots of branching paths, it's harder to tell what it was doing.

    ## Troubleshooting

    - If you see `": This command uses shell operators that require approval for safety

Claude Model

Not sure / Multiple models

Is this a regression?

Yes, this worked in a previous version

Last Working Version

1.0.53

Claude Code Version

1.0.124

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

VS Code integrated terminal

Additional Information

I permalinked the slashcommand with the issue above. The workaround is:

Workaround:
`!`  <-- replace this
!    <-- with this

the slash command in the main of my repository doesn't trigger this anymore because of the workaround.