How TypeScript's `never` Type Eliminates Entire Classes of Runtime Bugs

TypeScript's `never` type represents values and code paths that are provably unreachable, allowing the compiler to enforce exhaustive handling of all union type variants. When developers add new variants to a union but forget to update corresponding handlers, the compiler raises an error before deployment rather than allowing silent failures at runtime. The pattern involves assigning an unhandled narrowed value to a `never`-typed variable, which acts as a compile-time contract enforcer. This approach also helps design "impossible states" — type structures where contradictory properties simply cannot coexist, removing the need for defensive runtime validation. Distinguishing `never` from related types like `void` and `undefined` is essential, as each carries a distinct meaning around reachability and return behavior.