feat: /freeze skill — restrict file edits to a scoped directory

[josephfung]

Idea

Add a /freeze skill that activates a PreToolUse hook on Edit and Write tool calls, hard-blocking any file modifications outside a declared directory. The scope is set by writing a path to ~/.trimkit/freeze-dir.txt and cleared when the skill is deactivated.

Goal

When debugging or investigating a specific part of a codebase, accidental edits to unrelated files are a real risk — especially when Claude is running autonomously. /freeze enforces scope discipline: you declare where work should happen, and edits outside that boundary are denied.

Example workflow

/freeze src/auth/
# Claude is now restricted to editing files under src/auth/
# Any Edit or Write call outside that path is hard-blocked with a clear message

/freeze off
# Scope restriction lifted

Implementation approach

1. Add skills/freeze/SKILL.md — skill prompt that:
   • On activation: resolves the given path (handling symlinks via pwd -P), writes it to ~/.claude/sysops/freeze-dir.txt, confirms to user
   • On deactivation (/freeze off): removes ~/.claude/sysops/freeze-dir.txt
2. Add hooks/check-freeze.sh — PreToolUse hook on Edit and Write tools that:
   • Reads ~/.claude/sysops/freeze-dir.txt (if file doesn't exist, allows everything)
   • Resolves the target file path and checks if it falls within the freeze boundary
   • Returns {"permissionDecision":"deny","message":"Edit blocked: outside freeze boundary (<path>). Run /freeze off to lift restriction."} if outside
3. Register the hook in settings/hooks.json scoped to the skill
4. Update install.sh accordingly

Notes

• Hard-block (deny), not warn-and-confirm — scope violations are never intentional during a freeze
• Gracefully allows everything when freeze-dir.txt doesn't exist (no-op when skill is inactive)
• Pairs naturally with debugging workflows: activate before starting, deactivate when done
• Could later be extended to support multiple allowed paths