The gate still let the retry run on hosts unsloth does not support, which is
where it is most harmful: a 7 GB macOS runner lost the Studio server 26 s into a
load, and the Linux runner was torn down mid-generation. Neither MPS nor plain
CPU can complete the import, so the retry there pays the cost and fails anyway.
Require an accelerator unsloth actually supports (CUDA/ROCm via torch.cuda, or
XPU), with UNSLOTH_ALLOW_CPU as the documented override, and hoist the predicate
to module level so it is tested directly rather than through the import system.
On a CPU-only host the retry no longer fires at all; on CUDA the clean-environment
case it was added for still passes 29/29.
