Use whenever Cytnx must be built or tested: configuring or building any CMake preset, compiling after an edit, running C++ (gtest/ctest) or Python (pytest) tests, deciding how much of the suite to run, anything GPU/CUDA-related on a machine with or without a GPU, or verifying a change with a quick standalone program against libcytnx.a. Do not compose pip/cmake/ctest commands by hand — this skill's script is the one entry point.
Use whenever a performance claim must be made or checked: a change is motivated by speed, a reviewer questions a speedup or regression, a PR needs before/after numbers, or two implementations/revisions must be timed against each other. Never assert performance from reasoning or a scratch timing loop — run this skill's benchmark procedure instead.
Enforce the Google C++ Style Guide as adopted by Cytnx when writing, reviewing, or refactoring C++ or CUDA (.cpp/.hpp/.cu/.cuh) code. Use when creating new C++/CUDA files or symbols, naming types/functions/variables, choosing parameter-passing conventions, or reviewing a C++ diff for style. Covers Cytnx's naming rules (snake_case for new code, no leading underscore, trailing-underscore in-place mutators), pass-scalars-by-value, includes, error handling, and the clang-format v14 boundary.
Enforce the Google Python Style Guide when writing, reviewing, or refactoring Python code in Cytnx — the `cytnx/` package, `pytests/`, `tools/`, and `example/`. Use when creating new .py files or symbols, naming, writing docstrings or type hints, structuring imports, or reviewing a Python diff for style. Covers naming, imports, Google-format docstrings, type annotations, error handling, and doctests.