Function cost_report 

pub fn cost_report(plan: &Plan) -> String

beck explain cost — what one event costs this view.

20 §20.5 left this command unbuilt with a reason rather than a shrug: beck explain place already prints every candidate’s cost, and “whether a separate cost view earns its place is a question for when there is a second cost dimension to show”. The plan is that second dimension. Placement costs are about where a definition runs, once, at compile time; these are about what the program does per event, for as long as it is running, and no placement decision can see them.