The codec specs a writer emits: brotli .br always (the universal fallback -- every Node ships it), plus zstd .zst when this Node can produce/read it. So a .br fallback is guaranteed next to every .zst.
.br
.zst
The codec specs a writer emits: brotli
.bralways (the universal fallback -- every Node ships it), plus zstd.zstwhen this Node can produce/read it. So a.brfallback is guaranteed next to every.zst.