Cross-executor parity test corpus

Goal

A spec test corpus pins every case the proposal decides and proves evaluator/LLVM parity, so a future regression on either backend fails immediately.

Implementation Sketch

Author tests/spec/modules/ corpus: newtype constructor import + construction; explicit variant import + construction; aliasing (T as U, Circle as Ring); within-rank collision #compile_fail negatives + as positives; variant-pattern type-directed resolution (import type only, match variants); binding-name/scrutinee-variant collision #compile_fail; orphan-variant import; pub use re-export propagation. Every positive pin runs on BOTH the evaluator and the LLVM backend (debug+release) and asserts identical results. Includes the north-star parity fixture tests/spec/modules/selected_type_import_parity.test.ori.

Spec References

Proposal (all Design + Error Handling cases); tests.md (matrix + negative pins + cross-executor parity); CLAUDE.md Fix Completeness (dual-execution parity).

Work Items

• Author the tests/spec/modules/ parity corpus (newtype/variant/alias/collision/pattern/orphan/re-export), each positive pin asserting identical evaluator vs LLVM results (debug+release); north-star parity fixture included.