/**
 * overlayStack.ts — which modal surface currently owns the keyboard.
 *
 * Every modal organism here (Sheet, Dialog, ConfirmDialog) listens for keydown on
 * `document`, so when one is raised BY another — `OrderCreateSheet`'s discard guard
 * opening a ConfirmDialog over its own Sheet — both handlers see the same key. Left
 * alone, Escape dismisses two layers at once and the lower surface's `trapFocus`
 * drags focus out of the upper one (`focusTrap.ts`'s FIX-466 clause pulls focus back
 * in whenever the active element sits outside its container).
 *
 * WHY A STACK AND NOT `event.target.closest('[role=dialog]')`:
 * that was the first attempt, and it has a real race. A modal moves initial focus on
 * a `setTimeout(0)` (deferred so the portal paints first), so between "ConfirmDialog
 * opened" and "focus arrived in it" the event target is still the Sheet underneath —
 * and in that window BOTH handlers ran. Reproduced: one Escape produced
 * `onCancel: 1` AND `onClose("escape")`. Ownership therefore cannot be derived from
 * where focus happens to be; it has to be registered explicitly.
 *
 * Registration order IS stacking order: each surface registers from its `[open]`
 * effect, so the most recently opened one is last and owns the keyboard until it
 * unregisters. Non-modal anchored panels (Select/Combobox/DatePicker — `listbox`
 * and `combobox` roles) deliberately do NOT register: they are not modal layers, so
 * the Sheet keeps owning Tab while one is open and FIX-466's portaled-focusable
 * wrap still applies.
 *
 * BEHAVIOUR NOTE: with two modals open at once, Escape now dismisses only the
 * topmost. Previously both closed on a single press. (NB-SHEET-DISMISS-01)
 */
/**
 * Registers `el` as the topmost modal surface. Returns the matching unregister —
 * call it from the same effect's cleanup.
 */
export declare function registerOverlay(el: HTMLElement | null): () => void;
/**
 * Whether `el` is the modal surface that should handle a keyboard event right now.
 *
 * An empty stack means nothing has registered — the caller handles the key, which
 * keeps every pre-existing single-overlay case behaving exactly as before.
 */
export declare function isTopmostOverlay(el: HTMLElement | null): boolean;
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