api: top-attesters / top-schema-owners / top-attestor-sets leaderboards

[proofmancer]

Why

Grafana wants "who's using the chain most" panels — top attesters, top schema owners, top attestor sets — alongside the existing ops + cost + economy dashboards (chain v0.2.11). Prometheus is wrong for this (address labels = unbounded cardinality), so the data needs to live in the api with Grafana pointing at it via the Infinity HTTP-JSON datasource. Filed during the 2026-05-22 session as part of Track 4 "full cost metrics" closeout — leaderboards were the second half of that ask.

What

Three new endpoints, all read-only, all sourced from existing indexer tables:

Endpoint	Source	Cost
GET /v1/stats/top-attesters?n=10	attestations GROUP BY submitter	one indexed scan; attestations is small (devnet: ~20 rows)
GET /v1/stats/top-schema-owners?n=10	schemas GROUP BY owner	one indexed scan; schemas is tiny (devnet: ~8 rows)
GET /v1/stats/top-attestor-sets?n=10	attestor_sets ORDER BY schema_count DESC	single index scan — schema_count is denormalised by ingest, no GROUP BY

All three return the same LeaderboardResponse shape:

{
  "window": "all-time",
  "rows": [
    {"rank": 1, "address": "lig1…", "count": 7},
    {"rank": 2, "address": "lig1…", "count": 5},
    …
  ]
}

Same {rank, address, count} row shape across all three means Grafana table panels can use one template per leaderboard. address is lig1... for the first two (rollup addresses) and las1... for top-attestor-sets (attestor-set ids) — same column, different identifier space, documented in the endpoint help.

Query params: n defaults to 10, capped at 100. 30s in-process cache + Cache-Control: public, max-age=30 matching the rest of /v1/stats/*.

Followup

• File a chain issue to add an "Activity leaders" row to ops/grafana/ligate-node.json once the Grafana Infinity datasource is provisioned. Three table panels, one per leaderboard.
• Future: time-windowed variant (?since=24h / ?since=7d) that JOINs on transactions.indexed_at for "who's been most active this week." Response shape stays the same; window field changes from "all-time" to the requested interval.

Net diff

3 files (crates/api/src/stats.rs +204, crates/api/src/main.rs +5, CHANGELOG.md +5).