Constant MAX_STATUS_MESSAGE_BYTES 

pub const MAX_STATUS_MESSAGE_BYTES: usize = _; // 4_096usize

gRPC status/trailers live in HTTP/2 HEADERS frames. Keep well under the default SETTINGS_MAX_HEADER_LIST_SIZE (~16–64 KiB) so large Nix stderr cannot GOAWAY the plugin connection with header_list_way_too_large.