Module language 

Language adapters.

Each supported language is a single self-contained [LanguageAdapter]: it declares the file extensions it owns, parses source into the shared ModuleFacts, and resolves its own import specifiers against the shared ResolveCtx. The registry below is the one place languages are enumerated — discovery (fs), parse dispatch (parse), and import resolution (resolve) all derive from it, so adding a language is a single new adapter plus one registry line.