newskill — add a skill without drift

/newskill scaffold <name> "<description>" <category> — create a new skill, registered /newskill fix [<name>] — complete a skill that exists in some surfaces but not others

A skillhub skill lives in four surfaces, and it is only really "added" when all four agree:

1. Folder — .claude/skills/<name>/SKILL.md with valid frontmatter.
2. README table row — a row in the right category table (a prose mention does not count; the validator checks for a table row specifically).
3. Marketplace — <name> listed in one plugin's skills[] in .claude-plugin/marketplace.json.
4. Trigger evals — cases in evals/triggers.json (model-invoked skills only; user-invoked skills are exempt).

Drift is these four disagreeing — the default failure of hand-adding a skill. The oracle for drift is python3 scripts/validate-skills.py: it already reports which surfaces are missing. This skill's whole job is to make the four agree and leave the validator green.

The loop (both modes end here)

Run python3 scripts/validate-skills.py → read each FAIL/WARN → fix that exact surface → re-run. Repeat until no FAIL. Never assert done from memory; the validator is cheap and authoritative.

Mode: scaffold

Adding a brand-new skill from a name + description + category.

1. Guard. If .claude/skills/<name>/ already exists, stop — this is a fix, not a scaffold; never overwrite an existing SKILL.md. Also reject a <name> that collides with a harness built-in (the validator's BUILTINS set) or an existing skill.
2. Folder. Write .claude/skills/<name>/SKILL.md with frontmatter (name = folder name) and a description. If out/tune/principles.md exists, read it before writing the body — each line is an authoring rule distilled from accepted past fixes. Keep the description ≤ 950 chars (soft limit; hard wall is 1024) — front-load the leading word, one trigger per branch. For a user-invoked tool add disable-model-invocation: true and write a human-facing one-line description (no trigger list).
3. Category → plugin + table. <category> is one of coding-loop / research / daily. Add ./.claude/skills/<name> to that plugin's skills[] in marketplace.json, and add one row to the matching README category table.
4. Trigger evals (model-invoked only). Add ≥2 cases to evals/triggers.json, including a routing pair against the nearest neighbour skill. Skip for user-invoked skills.
5. Pre-flight the body's snippets. Every snippet the new SKILL.md embeds is tried once against real data before the skill ships, output quoted in-session: execute each bash line (placeholders filled with real values), fetch each API endpoint, read each referenced path. A snippet that fails as written is a bug in the skill, not a formatting nit. Two honest outs, both flagged unverified and never skipped silently: one that can't run here (external account, missing binary, a file that exists only mid-run), and one that would mutate real state — never run something destructive just to prove it. This is tune's prove-the-rules-bite extended from config to authoring. (Fix mode is exempt — it never writes a body.)
6. Run the loop above until green.

Completion criterion: validator prints no FAIL; the new <name> appears in all four surfaces it's required in; every embedded snippet has run clean or is flagged unverified.

Mode: fix

Completing a skill that already drifted (e.g. a folder with no registration).

1. Diagnose. Run the validator; it lists exactly which surfaces <name> (or every skill, if <name> omitted) is missing from.
2. Register only — never rewrite the body. Fill each missing surface: marketplace entry, README table row, trigger cases. Touch SKILL.md only if the validator flags the frontmatter itself (e.g. description over the 1024-char limit) — and then edit the frontmatter alone, leaving the body unchanged.
3. Run the loop until green.

Completion criterion: validator prints no FAIL; the previously-missing surfaces now list <name>, and its SKILL.md body is unchanged.

After a description change — run the eval

Adding or rewording a model-invoked description changes the skill's only trigger surface, so a green validator is necessary but not sufficient. Re-run the trigger eval per evals/README.md (a fresh judge sub-agent over evals/triggers.json using validate-skills.py --descriptions): confirm the skill wins its own prompts and doesn't steal a neighbour's. User-invoked skills carry no description reach, so this step doesn't apply to them.