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.

Working rules

• Preserve the repository's sanctioned idioms and ABI; do not turn a scoped fix into a restyle.
• State ownership, check fallible calls, validate public boundaries, and assert internal invariants.
• Preserve recovery outside optimizer assumptions. An assertion that becomes an assumption can remove the branch handling its false case. Keep recoverable checks as runtime branches with diagnostic-only assertions behind a debug preprocessor guard. Exercise the fallback in an optimized release build.
• Guard staged initialization against reentry. Set an in-progress marker before callback-capable work on every constructor or factory path. Permit retry after failure only after fully releasing and resetting partial state. Test recursive entry and retry after failed initialization.
• Bound traversal of external input and check sizes before allocation or narrowing.
• Choose helpers only when they name a concept, own an error, or isolate a side effect.
• Verify the actual rebuilt artifact; use instrumented tests for safety and representative release builds for performance.

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.

Do not skip this gate. Established C codebases sanction idioms these rules would otherwise flag: