The notebook validation matrix caught the synthetic-data notebook dying
because the vllm server SyntheticDataKit launches never came up. Two
layers to the failure:
1. flashinfer's cpp_ext JIT shells out to ninja. The pip ninja lives in
the venv bin, which subprocesses like vllm serve do not always
inherit on PATH, so the JIT failed with exit 127. Install ninja-build
so the binary is reachable from any PATH.
2. With ninja present the JIT still cannot succeed for device code: the
runtime image deliberately ships no nvcc. Bake flashinfer-jit-cache
(cu128) so ops missing from the cubin package (fmha_gen on sm_100a
was the repro) come precompiled. In-process GRPO never hit this
because unsloth-zoo blocks the FlashInfer JIT path; standalone
vllm serve gets no zoo patches.
Fail-soft on the jit-cache for arches without a wheel; the vLLM chain
itself stays fail-loud on amd64.
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