write-c

name: write-c description: Recipe for writing new ANSI C99 runtime code in mino — module placement, GC discipline, error classes, the add-a-primitive and add-a-special-form rituals. Invoked by writer agents. user-invocable: false

Write new C for the mino runtime. The standards are .claude/skills/check-style/references/c-style.md (read it first) and the contracts in docs/ARCHITECTURE_CONTRACT.md; placement comes from docs/INTERNAL_MODULE_MAP.md; the why behind the constraints is the decision index (docs/adr/README.md) — scan it before designing anything that feels constrained by an unexplained rule.

Procedure:

Place it. Find the owning module in the module map; read that TU end to end before adding to it. New TU only when the responsibility is genuinely new — name it after the responsibility and add it to the map.
Follow the rituals. New primitive: the 4-step "How to Add a Primitive" in the module map (domain file → static signature → k_prims_<domain>[] row → tests; add to prim/internal.h only when the function crosses a TU boundary). New special form: the 5-step ritual below it. Don't improvise registration.
GC discipline up front. Decide ownership of every allocation before writing: GC-owned via gc_alloc_typed (pin temporaries across allocation points) or host-owned malloc (every error path frees). When a helper allocates twice, write the gc_depth/pin guard immediately — not after the bug.
Error classes. Every failure path picks its class consciously: MINO_ERR_RECOVERABLE via prim_throw_classified for anything user-catchable; MINO_ERR_HOST for limits/IO; abort() only with a why-unrecoverable comment. User input must never reach an abort.
Verify like the matrix. ./mino task build (the -Werror flag set is the floor), then the module's tests, then ./mino task qa-arch if you grew a TU. Sanitizer lanes run at the landing wave — but if you wrote pointer-heavy code, run ./mino task build-asan + the relevant test yourself.

Tests for new behavior go in tests/*_test.clj (language surface) or the C embed tests (ABI surface) — write them or coordinate with the write-tests dispatch, but never land implementation without them.

Public-facing text rule: never describe code as "hand-written" or "hand-rolled" in docstrings, docs, or changelog lines.