Function walk 

pub fn walk(stmts: &[Stmt<'_>], interner: &Interner) -> RecognizedProgram

recognize_stages over statements already parsed — every backend’s front end: the CUDA forward refuses what this walk reports as unrecognized or unlifted_writes, so both lanes agree on what a program’s statements are. The shape table is the caller’s to add (it comes from the parse, not the statements).