Keep cast --check from creating the bundle dir

[jmchilton]

Posted by Claude (AI assistant) on behalf of @jmchilton — not authored by them personally.

Closes #360.

runCastMoldCommand called mkdirSync(bundleRoot, { recursive: true }) before anything branched on args.check, so a read-only drift check against a never-cast Mold left an empty casts/claude/skills/<mold>/ behind. Git doesn't track empty dirs, so these were invisible in git status but broke tests/plugin-packaging.test.ts's SKILL.md-per-skill assertion.

Every other write in the check path (castOneRef, reconcileSkillMarkdown, _required_tools.json, _verify.json) was already guarded — the mkdir was the sole leak.

Regression test

tests/cast-mold.test.ts — "--check on a never-cast mold leaves no bundle directory behind": temp repo, minimal Mold with no refs, cast m --check → nonzero exit, SKILL.md drift reported, casts/claude/skills/m absent. Confirmed red-to-green.

Verification

• Issue's reproduction: cast validate-cwl --check reports both drifts, exit 1, no dir created.
• Repo-wide --check scan over all content/molds/*/index.md: find casts/claude/skills -type d -empty returns nothing.
• npm run test 151/151, typecheck 0 errors, packages-test, packages-format, packages-lint, validate (0 errors) all pass.

🤖 Generated with Claude Code