The variable picks the deepinfer/_so/<accelerator>-<arch> directory that holds
the extension module. The build scripts already reject anything but
nvidia/ascend (build.sh, scripts/build_vendor.sh), but the runtime accepted any
string: a typo such as "ascned" was silently coerced to the nvidia platform tag
in _so_platform_tag(), so the process looked for a directory that does not exist
and failed with a bare ModuleNotFoundError for deepinfer._C that never mentions
the variable.
Validate the value with EnvVar.choice so an unsupported value fails fast at
import time with the variable name. The documented behaviours are unchanged:
unset -> nvidia, "nvidia"/"ascend" -> themselves, and the empty value still
means "let deep_cluster detect the accelerator".
DeepEP now records an HTTPS DeepJIT URL, so build_vendor no longer needs the git@github.com rewrite.
Co-authored-by: Shaoyuan Chen <chensy@deepseek.com>