Safe worktree slug validation

Skill vishuwa2004/cskill-agents/agents/codex/skills/safe-worktree-slug-validation

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Install

npx -y skills add vishuwa2004/cskill-agents --skill safe-worktree-slug-validation

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Ensure Git worktree slugs can never escape the managed workspace or inject traversal.

SKILL.md

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SKILL: Safe Worktree Slug Validation

Domain: git-worktree Trigger: Apply this when accepting user-provided prefixes for enter worktree and you need to guarantee no path traversal or invalid chars slip into the worktree directory. Source Pattern: Distilled from reviewed permission, shell-safety, and worktree-management implementations.

Core Method

Split a slug on /, reject segments that are empty, . or .., or contain characters outside a za z0 9, and enforce a maximum combined length before joining the cleaned segments into a deterministic branch name and path. Perform this validation synchronously before invoking any git commands so the CLI never creates directories outside claude worktrees.

Key Rules

Validate each /-separated segment independently so user evil and similar mashups fail early.
Enforce a total length cap (e.g., 64 chars) before git worktree add to prevent excessively long refs or paths.
Reject slugs with leading/trailing slashes or repeated .. segments even when a normalization would neutralize them.
Run this check before any git fetch, mkdir, or hook execution to avoid partial side effects.

Example Application

Any agent producing a worktree name for a release hotfix can reuse this skill: call the validator on the proposed slug, surface a concise error message if it fails, and refuse to call git worktree add until the slug is safe.

Anti-Patterns (What NOT to do)

Do not rely on git worktree add to detect traversal; it may silently create directories in unexpected locations.
Do not treat slugs as a single string (e.g., foo bar) without splitting, because multi-segment checks are necessary.
Avoid waiting until after mkdir or config changes—the validation must run before any side effects.