r27: explicit TORCH_CUDA_ARCH_LIST=12.1a in vllm-builder (stage-env loss -> sm120-only kernels)

docker-images/glm53-jovian-r27/Dockerfile

@@ -86,6 +86,11 @@ RUN bash /tmp/fetch-deps.sh
 
 FROM deps-fetched AS vllm-builder
 WORKDIR /workspace/vllm
+# Hard-declared (do NOT rely on stage-inherited ENVs): the buildkit build
+# has no GPU, so torch's device-capability autodetect is unavailable and
+# the wheel must be told the target arch explicitly (the r27 slip: kernels
+# came out sm120-only -> cudaErrorNoKernelImageForDevice at boot).
+ENV TORCH_CUDA_ARCH_LIST=12.1a GIT_PROTOCOL=0
 ARG DEEPGEMM_REF
 ARG VLLM_PRETEND_VERSION
 ARG SOURCE_DATE_EPOCH