ADR 0593 §1: buscompose's engine moves from mesh-sdk into mesh-grants/internal/buscompose, its golden
user lists unchanged; the controller's raise and assert code is left behind, and the merged switch
test runs inside the part's whole integration test.
Claude-Session: https://claude.ai/code/session_01NcbgfJ9Gum47zkFKWRaovL
