A metric is a reviewed definition
A catalogue names the table, the aggregation, the dimensions and the filters. Adding a metric adds a catalogue entry, not an endpoint. A request picks names from it and never carries SQL; every value is a bound parameter.
One store, many customers
Every query filters on the caller's scope, and a ClickHouse row policy applies the same scope to a query that forgot. Your backend authenticates the customer and translates its plan into groups and days of history: the service knows no plan names.
Events, traces and bodies
Metrics by range and up to two dimensions, events paged by cursor, every event of one correlation ID, and an event's archived request and response from S3 when the plan allows it.