ia-cpp-systems

# C++ Systems & Libraries Covers C++17 as the baseline, with C++20 features called out where a project's standard allows them. For plain C (manual lifetimes, status enums, native extensions), see the `ia-c-systems` skill. ## Repo conventions outrank this skill Check `CMakeLists.txt` for `CXX_STANDARD`, read `.clang-format` and `.clang-tidy`, and read two adjacent translation units before writing. Where they conflict with the rules below, they win. The conflicts that actually happen: | Local constraint | Consequence | |---|---| | `-fno-exceptions` | Error handling is codes or `expected`-alikes. Constructors cannot report recoverable failure, so use a fallible factory or construct a valid fallback state. `new (std::nothrow)` only where the project's OOM policy is to observe null and recover; plain `new` is fine where the policy is termination | | Standard pinned below C++17 | No `std::optional`/`string_view`/structured bindings/`if constexpr`; check before using any | | Public header is ABI-stable | No layout changes, no inline-function changes, no added virtuals: load the ABI reference | | Embedded or freestanding target | No RTTI, no dynamic allocation in hot paths, possibly no STL containers | ## Tooling | Tool | Purpose | |------|---------| | `cmake` | Build system; `CMAKE_EXPORT_COMPILE_COMMANDS=ON` feeds every other tool | | `clang-format` | Formatter, driven by the repo's `.clang-format` | | `clang-tidy` | Lint (`bugprone-*`, `performance-*`, `modernize-*`, `cppco...