Purpose:
This package provides reusable test helpers for Headless (behavior/a11y/keyboard/overlay).

Non-goals:
- No golden-first UI snapshots by default.

Invariants:
- Helpers must be usable across components without pulling UI baseline dependencies.

Correct usage:
- Use helpers to assert semantics, focus behavior, keyboard-only scenarios, and overlay lifecycle.

Anti-patterns:
- Tying helpers to a specific renderer implementation.

