/**
 * Copy slots: what each island's slots are, how long their copy may be, and
 * when visible copy is allowed to change.
 *
 * Two rules live here because the browser and the server must apply them
 * identically:
 *
 *   - The fallback sets the size. Each field's fallback defines its slot, so
 *     its length is sent with every request as that field's length budget
 *     (`len.<field>=<characters>`), and the server writes copy to fit. The
 *     server read and the browser's stream compute the budget with the same
 *     function, so they ask for, and cache, the same copy.
 *   - Visible copy changes only on a visitor's action. A change to what an
 *     island would show (a context or campaign change) replaces visible text
 *     only when the visitor caused it: the interaction handler calls
 *     `markVisitorChange()` before it updates state. Any other change waits
 *     until the slot is off screen or the next page view.
 */
import type { CopyField } from "./state.js";
/** The copy fields each island has. */
export declare const ISLAND_COPY_FIELDS: Readonly<Record<"hero" | "cta", readonly CopyField[]>>;
/** Prefix of the length-budget query parameters: `len.headline=42`. */
export declare const LENGTH_PARAM_PREFIX = "len.";
/**
 * The length of copy as a length budget counts it: Unicode code points, so
 * an emoji or an accented letter written as one character counts as one.
 */
export declare function copyLength(text: string): number;
/**
 * The length budget per field: the length of each field's fallback, for the
 * fields named in `fields` whose fallback is not empty. A field without a
 * fallback has no slot and no budget.
 */
export declare function lengthBudgets(fallback: Partial<Record<CopyField, string | undefined>> | null | undefined, fields: readonly CopyField[]): Partial<Record<CopyField, number>>;
/** Add `len.<field>` parameters for `budgets`, in field order. */
export declare function setLengthParams(params: URLSearchParams, budgets: Partial<Record<CopyField, number>> | null | undefined): void;
/**
 * How long a `markVisitorChange()` call stays valid for the change it
 * announces: the state update it precedes renders well inside this.
 */
export declare const VISITOR_CHANGE_WINDOW_MS = 1000;
/**
 * Announce that the visitor caused the next change to what islands and
 * fragments show — call it in the interaction handler (a click, a submit, a
 * choice) before the state update that changes their campaign, context or
 * declaration:
 *
 * ```tsx
 * onClick={() => {
 *   markVisitorChange();
 *   setAudience("teams");
 * }}
 * ```
 *
 * Visible copy then changes once, with one cross-fade. Without it, a change
 * keeps the visible copy until the slot is off screen or the next page view.
 */
export declare function markVisitorChange(): void;
/** Internal: the current visitor-change generation, to remember as seen. */
export declare function visitorChangeGeneration(): number;
/**
 * Internal: has the visitor announced a change since generation `seen`, recently
 * enough that the change being rendered now is the one they caused?
 */
export declare function isVisitorChange(seen: number): boolean;
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