Reference
C5 floor closed: foreign values enter as unknown; every shape-assuming use vetoes until match-narrowed.
as Concrete laundering of unknownWhole-value bind, call, JSX, arg-pass can stay clean when no shape is assumed — the checker’s job is to stop silent structure trust.
Record-pattern match with runtime checks (nested + arrays). Decision trail: D57, D84–D91 in docs/07-decisions.md.