/**
 * The narrow-viewport flag — the one place the mobile breakpoint is defined.
 *
 * Below `NARROW_MAX` the Explorer folds its chrome into one off-canvas nav:
 * the top bar's section tabs join the sidebar tree behind a burger, and the
 * resizable preview stages drop their drag handles — there is no room to drag
 * into and no pointer to do it with.
 *
 * Anything that is only paint keys off `@media (max-width: 860px)` directly,
 * so a prerendered page comes up narrow on the first frame instead of
 * reflowing once hydration runs. This module covers the rest: markup that must
 * not exist at all on a phone, and behaviour (a stored desktop stage width) a
 * media query cannot reach. `tests/explorer/viewport.test.ts` asserts every
 * max-width query in the package equals NARROW_MAX, so the two cannot drift.
 */
/** Widest viewport still treated as a phone, in px. */
export declare const NARROW_MAX = 860;
/**
 * Start tracking the viewport (Explorer calls this on mount).
 * Returns the unsubscribe callback.
 */
export declare function initViewport(): () => void;
/** True on phone-width viewports. Reactive; false until `initViewport`. */
export declare function isNarrow(): boolean;
/**
 * Cap a page's horizontal padding for a narrow screen.
 *
 * `padding` is authored for a desktop column, where 32px a side reads as a
 * margin; on a 390px screen it is a sixth of the width. Each horizontal slot
 * of the shorthand becomes `min(<authored>, 16px)`, so a page that asked for
 * *less* keeps less and a full-bleed page stays full-bleed. Vertical slots are
 * untouched. Zero lengths pass through — `min(0, 16px)` mixes a number with a
 * length and would invalidate the declaration. A value built from calc()/var()
 * is returned as authored rather than mis-parsed.
 */
export declare function capSidePadding(padding: string | undefined): string | undefined;