State

Core engine: src/rpn-calculator.js
Default demo: samples/dev/ classic browser demo; samples/calc-02/ remains the portrait-first HP48GX-inspired reference
Public API: push, pop, clear, swap, remove, edit, isValidIndex, input, command, getOperationsByCategory, getConstants, listConstants, setConstant, removeConstant, hasConstant
Config: maxSize, base, angleMode, enabledCommands
Commands: arithmetic, stack, trigonometry, constants pi, e, phi, g, and c; arithmetic includes root with y√x, yroot, and nroot aliases; constants can be added or removed dynamically through the core API
Demo behavior: samples/dev/ keeps hidden input focus on desktop and supports clipboard paste; samples/calc-02/ uses compact mode/constants popups, a 4-column display-adjacent row, stack selection/move mode, and paste through the hidden input
Exports: browser window.RpnCalculator, CommonJS module.exports