D349 - POSIX spellings delegate to the vendor implementations

Status: decided Date: 2026-09-26

orbistoun-posix declares the POSIX library's names and serves each one with a vendor-named twin by delegation: a table maps the name to the twin's function pointer and arity, looked up from the implementing crate. Where the spellings differ in arity they have separate entry points, and a failure returns the project's placeholder rather than an errno.

Why: a NID is the hash of a name, so a behaviour already implemented is unreachable until its second spelling is declared. Delegation copies nothing, so the two cannot drift. A shared body cannot see which arity called it and reads an argument the shorter spelling never passed. An invented errno is a plausible wrong answer; the placeholder sends a switching caller to its default branch.

Rejected:

• Copied implementations per spelling: drift.
• A rule-generated mapping: "mostly mechanical" binds some names wrongly.
• One body for two arities: reads a register the caller never set.