Function lower_type_item_ir 

pub fn lower_type_item_ir(
    decl: &Arc<TypeDecl>,
    program: &CheckedProgram,
) -> IrItem

P6.6 (#1161): lower a type declaration into a real IrItem::Type — IrItem’s own doc comment names which of its seven design-sketch variants are real as of this slice (Type/Fn only, Decision D). Takes a certified &CheckedProgram, matching this module’s own categorical discipline (this file’s own header doc: “every entry point here takes a &CheckedProgram”), even though only TypedCommons::types/ty_intern are read — no per-expression expr_types lookup is involved (Q2, design/tracks/the-ir.md §3.2), but which fields are read isn’t the discipline; which failures are allowed to panic! is. Every panic below asserts “the checker already accepted this declaration” — true only once certify has run: a bare TypedCommons is not certified by construction (checker.rs’s own CheckedProgram doc notes the project/batch path holds per-unit TypedCommons values before that unit’s build-wide gate is decided), so accepting one here would make resolve_type_ref_in returning None a reachable, not just a buggy, outcome.