foundry-build cast --check creates its destination directory

[jmchilton]

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

foundry-build cast <mold> --check is a read-only drift gate, but it creates the bundle directory as a side effect. On a Mold that has never been cast, this leaves an empty casts/claude/skills/<mold>/ behind.

Cause

packages/build-cli/src/commands/cast-mold.ts:1266 — mkdirSync(bundleRoot, { recursive: true }) runs unconditionally in runCastMoldCommand, before anything branches on args.check.

Reproduction

$ rm -rf casts/claude/skills/validate-cwl
$ test -d casts/claude/skills/validate-cwl && echo YES || echo NO
NO
$ npx tsx packages/build-cli/src/bin/foundry-build.ts cast --root . validate-cwl --check
drift: SKILL.md — SKILL.md missing
drift: _verify.json — verify manifest missing
check failed: 0 error(s), 2 drift(s)
$ test -d casts/claude/skills/validate-cwl && echo YES || echo NO
YES        # empty

Why it bites

tests/plugin-packaging.test.ts (keeps non-skill artifacts outside the discovered skills directory) enumerates real directories under casts/claude/skills/ and asserts each has a SKILL.md. Git doesn't track empty directories, so these are invisible to git status — the failure looks like it came from nowhere.

Running a repo-wide drift scan is the natural way to answer "what's stale?":

for f in content/molds/*/index.md; do
  m=$(basename $(dirname "$f"))
  npx tsx packages/build-cli/src/bin/foundry-build.ts cast --root . "$m" --check
done

That currently creates one empty dir per uncast Mold (14 at the moment — the CWL and paper Molds, repair-galaxy-draft-topology, paper-to-test-data) and breaks an unrelated test until they're cleaned with find casts/claude/skills -type d -empty -delete.

Suggested fix

Skip the mkdirSync when args.check is set, or defer it to the first actual write. A --check run that finds drift should report it without touching the tree.

Worth a regression test: --check against a never-cast Mold should leave no directory behind.

Context

Found while closing out #322 residue (#359).