How does Ruby optimize constant lookup using lexical scope caching?

Ruby caches constant resolution based on lexical nesting and invalidates on namespace changes.

Constant lookup first checks lexical scope (where code is defined), then outer scopes, then inheritance chain. To optimize repeated lookups, Ruby caches resolved constants with version tags tied to module/class definitions. If structure changes, cache is invalidated. This avoids repeated expensive namespace traversal in deeply nested modules.