The format's accepted kind gains stream (check or delivery), so the build seats' step on both streams and run on check validate against it; the class description says a verb that names no class takes read, on main or added in G, and that nothing refuses it. Builds: design 47 G §455, §456 Claude-Session: https://claude.ai/code/session_01JG73KEq4zoDfM9WtYpcQgZ