FLX-3004: expose schema cannot be compiled into an ordered column set

Family: seam/conformance (the 3000 band)

The seam needs an ordered, non-empty list of uniquely-named columns: rows travel as arrays aligned to that order (KERNEL-SPEC §8), so a missing schema, an empty one, a column with no name, or two columns that share a name after NFC normalisation leaves no way to place a value. The declaration is refused rather than repaired.

Look it up offline

$ fluxsim explain FLX-3004

Every code is listed in the error index.