//! PNC engine — arbitrary-precision RPN calculator core.
//!
//! Provides values, units, operations, parsing, stack history, and persistence.
//! The engine is a pure library with no I/O; the binary crate (`pnc`) owns
//! frontends (TUI/CLI), logging, and terminal lifecycle.
pub use PncError;
pub use DisplayMode;
pub use Dimension;
pub use UnitId;
pub use Value;