#library already lexes/parses (library_decl node); extern/export are keywords. Phase 1 new work pinned to concrete sites: parser (extern(.zig) postfix at the #builtin/#compiler positions), AST binding field, compiler_hooks.zig as the registry, types/llvm layout emission, host_ffi comptime bridge. First testable sub-step: extern(.zig) <lib> parses on a fn decl.