D352 - ABI constants are harvested from FreeBSD headers

Status: decided Date: 2026-09-26

orbistoun-gen constants <checkout> harvests #define constants from a fixed list of FreeBSD headers into crates/orbistoun-hle/data/abi-constants.toml, stamped with the revision git rev-parse HEAD reports; the gate regenerates and diffs it. Code reads values from the table and never retypes them. Composite expressions and function-like macros are skipped.

Why: implementing needs interface numbers, and a public header constant is an ABI fact like a symbol name. The values are FreeBSD's, so each is published about FreeBSD and assumed about the guest. Reading from the table keeps a harvested constant distinguishable from a remembered one. Taking the revision as an argument let a hand-edited header regenerate to itself; a checkout that is not a repository is refused. Absent the checkout, the gate step warns and passes.

Rejected:

• Constants typed into Rust: untraceable.
• A revision passed on the command line: the header could name any source.
• A directory walk: hundreds of constants nobody asked for.
• Evaluating composite expressions: reproduces a decision instead of reading a number.