fix(openclaw): reject path-escaping import skill names

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Summary

• Fixes critical path traversal in skilllite import-openclaw-skills (and claw migrate skill import): SKILL.md frontmatter name was joined under the skills root without single-segment validation, so absolute or ../ names could install outside skills/.
• Adds shared validate_skill_dir_name / skill_dir_under_root helpers (aligned with open PR fix(security): reject path-escaping skill directory names #125) and fail-closed skip of unsafe destinations before copy.
• Adds regression tests for relative and absolute escape attempts while keeping safe sibling skills importable.

Task Linkage

• Task ID: TASK-2026-079
• Task folder: tasks/TASK-2026-079-openclaw-import-dest-name-safety/

Injected Specs

• spec/verification-integrity.md
• spec/task-artifact-language.md
• spec/security-nonnegotiables.md
• spec/rust-conventions.md
• spec/testing-policy.md
• spec/docs-sync.md (reviewed; no docs needed — fail-closed validation only)

Validation Evidence

• Commands executed:
  • cargo test -p skilllite-core path_validation
  • cargo test -p skilllite-commands import_
  • cargo fmt --check
  • cargo clippy -p skilllite-core -p skilllite-commands --all-targets -- -D warnings -A dead_code -A clippy::question_mark -A clippy::useless_borrows_in_formatting
  • python3 scripts/validate_tasks.py
• Key results:
  • path_validation: 3 passed
  • import_: 4 passed (relative + absolute escape skipped; safe skill still installed)
  • fmt clean; clippy clean with known main allow categories
  • task validation: Task validation passed (71 task folders checked)

Regression Scope

• Areas likely affected:
  • import-openclaw-skills destination selection
  • claw migrate skill import (delegates to the same command)
• Explicit non-goals:
  • skilllite add / MCP / CLI lookup validation (open PR fix(security): reject path-escaping skill directory names #125)
  • Pending evolution confirm/reject (open PR fix(evolution): constrain pending skill path operations #89)

Docs Sync (EN/ZH)

• Not needed
• Updated EN + ZH docs
• Files:
  • N/A

Review Checklist

• Acceptance criteria in tasks/TASK-2026-079-openclaw-import-dest-name-safety/TASK.md satisfied
• tasks/TASK-2026-079-openclaw-import-dest-name-safety/STATUS.md updated with latest progress
• tasks/TASK-2026-079-openclaw-import-dest-name-safety/REVIEW.md includes merge readiness decision
• tasks/board.md status is up to date

Security review notes

• What security policy changed, and why is it needed? Fail-closed single-segment validation for OpenClaw import destination names before skills-root joins; prevents filesystem escape via malicious frontmatter during import.
• Is default behavior more permissive? No — stricter validation only.
• Does this affect SKILLLITE_* config semantics or backward compatibility? No env/config change; only rejects previously unsafe multi-segment/absolute names.
• Were tests and EN/ZH docs updated? Tests yes; docs not required.