Tests

Matrix

• Return types: void, bool, reference type, value type.
• Calls: instance vs static, generic, value‑type receiver under constrained..
• Occurrences: single, multiple with index selection.
• Skip behavior: inner prefix returning false with and without preset __result.
• Argument mutation:
  • Inner mutable by‑ref arg modified by prefix and by original.
  • Outer arg modified via o_param by‑ref.
  • Outer local via _var<index> by‑ref.
• Synthetic locals: _var<name> shared across inner pre/post.
• Coexistence with outer prefix/postfix and with transpilers.

Assertions

• Correct ordering and skip semantics.
• Identical stack effect to original call.
• Correct write‑backs for by‑ref when used.
• No change in behavior when no infix patches apply.

Scaffolding

• Build tiny outer/inner pairs with predictable side effects.
• For constrained. cases, use value‑type receivers with interface calls.