it run (about 3.5 min) and the two lower-std plus build cycles. Most turns went into finding the right forms: the signatures of process::run, fs::Path, process::Output and sha256_hex in std.contracts; how a host trait method that throws lowers (Box<dyn Error>); and that CheckWall had no impl Error. One lower-std round was lost to NK1102 (String? compared with String). sysroot_holds already did that check, so I reused it.process::run takes dir: ref String and Vec[String] arguments, so paths go through .display().Output has ok, stdout and stderr as text.CheckWall has no impl Error, and a thrown host error is boxed. That means the brief’s “driver throwing CheckWall” needs the RefCell pattern; the brief should have said so.Thrown::split() gets the error back on the Rust side; message() is pub(crate).sysroot_holds exists.cargo fmt uses edition 2024, so a plain rustfmt sorted the imports differently.nikaia check on the single file: half wasted, since it cannot see CheckWall in another file and gave a false NK1151.lower-std, cargo check of nikaia-std --features compiler, then cargo check, build, lower-std fixpoint, the four it filters, clippy, fmt, pre-push-check, badges.py.--lib grammar_run:: was wasted: the module has no unit tests.tests/compiler package the brief asks for. The run rules forbid suite-sized runs; the driver covers it.std.contracts signatures it relies on (process::run, Output, fs::Path::display/parent, sha256_hex(ref Vec[u8])) and the throwing-host pattern: keep the RefCell, rethrow a placeholder, return the kept value through Thrown::split().0. It would also say up front that CheckWall needs an impl Error.After my commit, grammar_run.nika changed on disk, probably another session’s edit. b070adb9 holds my version, and the driver should check whether the change is wanted.