FLX-3302: a required expose column has no runtime attribute mapped onto it

Family: seam/conformance (the 3000 band)

A scenario-driven emit renders each moment onto the expose's declared columns through the mapping :mod:flux_engine.seam.mapping resolves: an alias declared for the vertical, an override declared on the emit, or the column's own name matching a runtime attribute. A column the contract marks required that none of those three resolve leaves the row with no value to place, and a required column may not be null (FLX-3202) -- so the run is refused where the mapping is decided, before a row exists, rather than on every row it would produce. Declare the source under the emit's mapping block, or add the column to the vertical's alias table.

Look it up offline

$ fluxsim explain FLX-3302

Every code is listed in the error index.