Map: core / ty

core/src/ty.rs and core/src/ty/ are the type language as data, below the IR and the checker: the IR’s schemes and sites name it, and nothing in it reads a unifier or a runtime value.

• ty.rs: Ty, CompTy, Grade, Row, Label and the unification-variable newtypes; TAG_PREFIX, the sigil of a tag, written once.
• ty/kind.rs: Kind, the closed set of predicates a type variable carries (number, comparable, scalar, sized, data), their meet, and what a head is.
• ty/scheme.rs: Scheme, a type under quantifiers, and the weak-variable sets a scheme did not quantify.
• ty/exec_arg.rs: RefusedArg, the shapes execve(2) has no argument for, one match on a Head.
• ty/fmt.rs: Display for Ty and Scheme; one FmtCtx names a shared variable the same in every type a diagnostic prints.
• ty/site.rs: the data of a Site, a boundary’s checked type frozen as a graph of nodes (Node, Shape, Fields, Tail) naming its unit by a UnitId — an OS nonce drawn once per process and a count, so unique in every process that meets it, a baked prelude unit’s included. Fixings is not in the code: it is the session’s table of what each unit’s comparable variables were fixed to, keyed by (UnitId, var), which a session’s threads share and a new session snapshots (shell-state). The checker builds a Site (typecheck/site.rs), one fresh UnitId per unit, and the runtime walks it against the running session’s table (types/admit.rs).

Str, the shared immutable string a Value::String holds, lives in core/src/text.rs.