Public Skills Leaderboard — ranked by performance dimension within a window

Anonymous-readable, time-windowed ranked leaderboard.

Distinct from the registry browse endpoint:

• Registry /skills?sort= is about exploration (filter + paginate)
• This endpoint is about ranking (top N by performance dimension)

Axes (every axis is an earned place; each one’s gate is stated in the UI sub-copy):

• evidence (DEFAULT since 2026-08-15): the same measured-lift population as biggest_improvement, ordered so that a skill with MORE evidence legs outranks a single-leg skill — a lift that two independent instruments agree on beats a bigger lift only one instrument ever saw. Carries an evidence FLOOR (see evidence_floor) so an unmeasured seed cannot outrank measured work. Every row still reports its own legs, provisional flag and activations_30d, so the UI can label exactly how much evidence a row stands on rather than implying it is settled.
• skill_score: SkillScore v2 DESC. A skill charts once it has at least one evidence signal (≥1 leg); skills with no evidence never chart. Signal count is a tie-break, not an entry gate, so a provisional (single-signal) score still ranks — every row reports its own legs count and provisional flag alongside the score. At an equal score this axis orders by measured benchmark lift, then by a stable id. Rolling 30d rollup, so window_days does not apply to this axis.
• biggest_improvement: latest verified SkillTestRun in the window, pass-rate delta vs the no-skill baseline.
• efficiency: token savings ASC (most negative = cheapest); skills that INCREASED token cost are excluded. most_turn_savings is the legacy param for the turns-keyed variant and keeps working.
• top_rated: SkillRaterReport mean in the window, ≥10 rated traces (matches the v2 rater-leg gate).

category narrows every axis to one skill.category and re-ranks inside it, so the caller gets the top N of that category rather than whatever slice of it happens to reach the global top N. Unknown values return an empty board rather than a 400 — unlike sort, which selects a code path, a category is a data filter, and “no skills match” is a true answer. That also matches browse, which has filtered on the same column since forever.