Brummel
b252f837af
Address quality review of a9aa248:
- Replace string-prefix discriminator (`prior.starts_with("class ")`)
with a structural `Origin { Class | Fn }` enum; `kind` is now a
`match` on variants, formatting is reserved for error construction.
- Fix fn-fn collision misreport: in the `Def::Fn` arm, only fire
`MethodNameCollision` when the prior origin is a class. Two
`Def::Fn` with the same name are `CheckError::DuplicateDef`'s job
in `ailang-check`, not this pre-pass.
- Tests use `examples_dir()` like the rest of the module; path
construction is no longer ad-hoc.
- Tests assert `first_origin` / `second_origin` so an origin-format
regression cannot silently break the `kind` discriminator.
- Drop forward-looking 22b.4 prelude reservation note from the
variant doc — keep only what's load-bearing for 22b.2.