feat: directory-shaped skills with support files (COD-417)

[shivros]

feat: directory-shaped skills with support files (COD-417)

Closes COD-417.

Problem

Creed's skill model was one flat .md per skill. Real Hermes-style skills are directories — <name>/SKILL.md plus references/, templates/, scripts/, assets/ — and 174 of 307 real skills in the hermes-skills tree are directory-shaped. Declaring a directory skill emitted exactly one file and silently dropped every support file, exit 0, "0 failed". Separately, a skills-only source with only the agents target (context-only) was a silent no-op.

What changed

• domain.Skill gains Files map[string][]byte + IsDirectory(). Flat skills (nil Files) behave byte-identically to before.
• localfs.readSkillDirectory — a skill entry path that is a directory is walked with filepath.WalkDir: SKILL.md becomes the skill content; every other regular file becomes a support file keyed by slash-relative path. Symlinks and non-regular files are rejected (same containment discipline as single-file reads, via readContainedFile); a directory containing only SKILL.md is rejected with guidance to declare the file path directly. gitremote/layered delegate to localfs, so they inherit this.
• renderSkillDirOutput emits directory skills under <skilldir>/<name>/SKILL.md plus support files in sorted (deterministic) order. Flat skills still emit <name>.md.
• New internal/skillmeta — shared frontmatter parse/validate: when a skill carries YAML frontmatter, name must match the manifest entry and description must be present. Missing frontmatter is a warning, not an error.
• Sync enforces the contract at generation time (render fails on broken/mismatched frontmatter instead of byte-copying blindly); validate reports the same diagnostics for both directory and flat skills, with the file path and problem in each message.
• skills_have_no_output warning in validate when declared skills have no enabled target with a skill-dir output — kills the silent skills-only + agents no-op.
• Scaffold skill and creed's own two dogfood skills now carry the frontmatter contract; regenerated outputs.
• README documents directory skills, the frontmatter contract, and the no-op warning.

Verification

All run locally on this branch:

• go build ./... — pass
• go test -race -count=1 ./... — 11 packages ok
• go vet ./..., gofmt -l . — clean
• scripts/check-generated.sh — "generated code is current"
• Dogfood: built binary against creed's own repo — validate passes (incl. frontmatter contract on own skills), sync idempotent (second run 0 written, all skipped)
• New tests: localfs directory reads (happy/missing-SKILL.md/symlink/lone-SKILL.md), renderer tree emission + determinism + frontmatter enforcement, validate diagnostics table (dir + flat: mismatch/missing-description/no-frontmatter/unterminated), symlink rejection, no-output warning, end-to-end zero-data-loss sync with 5/5 file-count parity + idempotency

Notes

• The dual review panel (delegate_task) failed with runtime spawn timeouts (3×420s) this run; a detailed self-review found no blocking issues, and the deviation is logged in RUNNER.md. The Auto-Merge Gate evaluates this PR independently before any merge.
• Generated surfaces: no descriptor/signature changes — go generate produced zero drift.

[shivros]

Auto-Merge Gate — approved

Confidence: 0.86

Rationale: The implementation directly satisfies COD-417: directory entries read SKILL.md plus contained regular support files, emit the complete deterministic tree, retain flat-skill behavior, validate frontmatter at validation and render time, and warn on skills with no enabled skill-output target. The change includes focused unit and end-to-end idempotency/data-loss tests.

Checks observed: GitHub CI Test, Lint, Creed context drift, and Secret Scan all succeeded. Independent gate verification also passed:

• go test -race -count=1 ./...
• go vet ./...
• gofmt -l $(git ls-files '*.go') (clean)
• ./scripts/check-generated.sh

Scope limits: This approval covers COD-417 only. No unresolved review comments, manual-review markers, secrets/auth/deployment/billing/destructive scope, or merge conflicts were found.