Compiler Pipeline

At a high level, the compiler pipeline is:

1. Parse source into syntax structures.
2. Expand runtime meta { ... } forms into runtime AST.
3. Elaborate/concretize runtime types (instantiate generic struct templates into concrete runtime structs).
4. Lower into typed HIR.
5. Run checker passes.
6. Lower into MIR.
7. Emit Rust code and optionally execute it.

Checker invariant: runtime generic types are not supported past elaboration. If a generic runtime type survives into checking, it is treated as an invariant violation and rejected.

See README.md, Language Design (MVP), and the Metaprogramming reference.