/**
 * `?doc=` — which design is on screen, and the one value that is not an id.
 *
 * Here rather than in either panel because both read it and neither owns it: the list writes it, the
 * canvas answers it, and a constant that lives in one of them makes the other import a component to
 * get at a string.
 *
 * ── Why a sentinel and not an absent parameter ──
 *
 * Absent already means something: "open whatever I had last", which the canvas answers with
 * `/documents/latest`. A blank canvas is a different request, and expressing it by removing the
 * parameter made New hand back the design already on screen — then point the next save at its id.
 *
 * `new` is not a valid id, so nothing can collide with it: `Number('new')` is NaN and every document
 * route rejects that before it reaches the database.
 */
export const NEW_DOC = 'new';