Point prequant_repos for flux.1, flux.2-klein, flux.2-dev, qwen-image
(int8 only there; fp8 is family-denied), z-image and krea-2 at the
unsloth/<Model>-FP8 Hub repos carrying gate-validated int8 and fp8
transformer checkpoints, so the fast quant path loads the small
pre-quantized file instead of materialising the dense bf16 transformer
and quantising on device. Measured on FLUX.2-dev int8: build peak drops
from 60.7 GB (dense + quantize) to 30.7 GB (hosted prequant), identical
30.7 GB resident after either path since loading a checkpoint is
bit-identical to on-the-fly quantisation.
The hosted repos name files <Model>-<SCHEME>.pt, so resolve_prequant_source
now derives that model-name filename from the repo id (scheme suffix
stripped case-insensitively) and carries the legacy transformer_<scheme>.pt
as a fallback the resolver tries when the primary 404s, keeping older
repos loadable.
Wiring a repo also exposed a fallback hazard: with a prequant source
present, the dense-fit preflight used to be skipped entirely, so a failed
prequant download would fall through to the dense bf16 load the memory
plan never budgeted, OOMing after eviction. The preflight now always runs
and gates an allow_dense_fallback flag through _load_dense_quant_pipeline:
a dense misfit still skips the fast path when no prequant exists, but with
one it proceeds and a prequant failure raises to the GGUF build instead of
loading dense. The same flag is set when the auto-policy replans an
offloaded GGUF against a prequant-sized transient.
Tests updated to the new filename convention plus new coverage for the
derivation and the legacy-name fallback; the prequant-skips-refit test now
asserts the re-check runs and forbids the dense fallback. Verified end to
end on GPU: z-image int8 resolves the hosted repo, downloads the
model-name file and renders (6.8s load, 5.9 GB peak).
fbcf070fce