#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.
Unified sx<->compiler binding that subsumes the metatype declare/define
primitives AND the #compiler struct attribute. A named 'compiler' library
exposes the compiler's real types (layout-welded via extern(.zig), offsets
queried from the Zig type at compiler-build time + a build-time equality
assertion) and functions (comptime-only, host-call bridged). declare/
define/type_info become sx library code over register_*/find_type; the
projected meta.sx TypeInfo + hand marshaling are deleted; BuildOptions
migrates onto it and #compiler is removed. Includes the safety boundary
(curated export list, guarded mutators, comptime-only), the honest limit
(the ordering law stays, but stops leaking as 'weird stages' — dissolving
the 0141 class), a phased suite-green build order, and the open risks
(union(enum) welding, optional fields, LLVM offset emission).
