One seed colour -> a reproducible five-role colour system (field, ground, support, signal, accent) with Base/Light/Dark modes.

The seed hex (and any locked hex) is returned byte-identical in its role; nothing is snapped to the archive. Every response carries its recipe, recipe_hash and the exact algorithm_version. The same recipe and algorithm_version always produce the same colours; development builds get a new version id for any quality change, and retired ids return 410.

Omit seed_role to use the engine's recommended role (returned in role_selection with its reason).