The pipeline already loads its base_model VAE through VAELoader, so the
existing h3_vae_nvfp4_decoder swap applies; this exposes it: a
--h3-vae-nvfp4-decoder CLI flag, a --vae-decoder example flag, the serve
option in the regen2k YAML, and the measured 2K decode/quality table in
the guide.
CPU tests pin the regen2k VAE load applying the exported decoder, the
serve-config field reaching FastVideoArgs, and the new CLI flag.