ia-c-systems

# C Systems & Native Code Covers C11 and later for libraries, systems code, and native extensions. For C++ (RAII, templates, move semantics), see the `ia-cpp-systems` skill. ## Repo conventions outrank this skill Read the repo's `AGENTS.md`/`CLAUDE.md`, its public headers, and two adjacent `.c` files before writing anything. Where they conflict with the rules below, they win, and the diff carries no note about it. This gate is load-bearing. Established C codebases sanction idioms these rules would otherwise flag: | Local idiom | Where it is correct | |---|---| | Tab indentation | php-src and its extensions, Linux kernel | | `goto cleanup` / `goto err` | Kernel, OpenSSL, curl, php-src: the dominant multi-resource release idiom | | Macros containing `return` | `RETURN_*`/`RETVAL_*` in PHP extensions, `Py_RETURN_*` in CPython | | Project status types | `zend_result`, `CURLcode`, `int` plus `errno`: do not invent a parallel enum beside one | Never widen a scoped task into a repo-wide restyle because adjacent untouched C predates a rule here. **When the target is a PHP extension** (`php_*.h`, `PHP_FUNCTION`, `zend_`, `config.m4`), load [php-extension-c.md](./references/php-extension-c.md) before applying any rule below. Layout, macros, the error model, memory, and assertions all carry extension-specific overrides, and the memory one in particular inverts the base guidance: extensions use a request-scoped allocator, not `malloc`/`free`. ## Tooling | Tool | Purpose | |-----...