POST /api/metric/dataset

Execute a metric or measure-based query and stream the results.

Request body requires a definition object containing:

• expression: A metric math expression tree (leaf reference or arithmetic) Examples: [:metric {:lib/uuid "a"} 42], [:- {} [:metric {:lib/uuid "a"} 1] [:metric {:lib/uuid "b"} 2]]
• filters (optional): Per-instance filters keyed by :lib/uuid from the expression
• projections (optional): Typed projections keyed by source type and ID