# 013 — Dashboards: PromQL query support

## Summary

Support PromQL-style queries over declared metrics to derive dashboard
visualizations, per the README's Dashboards section ("There should be support for
promql queries to derive the visualisation").

## Scope

- Evaluate a useful PromQL subset (instant/range vector selection by metric name +
  label matchers, at minimum; consider `rate()`/`sum()`/`avg()` aggregations as
  stretch) against `Bucket` data ([003](003-metric-bucket-derivation.md)).
- Decide whether to hand-roll the subset or bring in an existing PromQL parser
  crate — document the choice.
- New `EngineQuery` variant for PromQL evaluation, following the existing
  single-owner-evaluates-in-place pattern.
- API endpoint (e.g. `GET /api/query?promql=...`) returning a chart-ready series
  format (labels + time-value pairs), shaped for bar/line/pie consumption by
  [014](014-dashboards-ui.md).

## Acceptance criteria

- A basic instant/range query against a declared metric with a label matcher returns
  correct series data against a seeded fixture.
- Malformed PromQL returns a 4xx with a useful error.

## Depends on

- [004 — Metrics API](004-metrics-api.md)