/**
 * Signal — Named reactive scalar for the prefab wire format.
 *
 * Signals carry identity values (string, number, boolean, null) — never
 * full objects. They serialize into `state` as a key-value pair and
 * produce `{{ key }}` expressions wherever they're referenced.
 *
 * @example
 * ```ts
 * const selectedId = signal('selectedPatientId', 'hans-meier')
 * // state: { selectedPatientId: 'hans-meier' }
 * // referenced as: "{{ selectedPatientId }}"
 * ```
 */
import { Rx } from './rx.js';
/** Allowed signal value types — intentionally excludes objects/arrays. */
export type SignalValue = string | number | boolean | null;
export interface SignalOptions {
    /**
     * URL query parameter name. When set, the runtime syncs the signal
     * value with `?param=value` in the address bar. Opt-in.
     */
    urlSync?: string;
}
/**
 * A named reactive scalar. Carries a state key, an initial value,
 * and produces rx expressions for component props.
 */
export declare class Signal<T extends SignalValue = SignalValue> {
    readonly key: string;
    readonly initial: T;
    readonly options?: SignalOptions;
    constructor(key: string, initial: T, options?: SignalOptions);
    /** Rx expression referencing this signal's value: `{{ key }}` */
    toRx(): Rx;
    /** Serialize to the rx template string */
    toString(): string;
    toJSON(): string;
    /** State entry for PrefabApp: `{ key: initial }` */
    toState(): Record<string, T>;
}
/**
 * Create a named reactive signal.
 *
 * @param key     Stable state path (e.g. 'selectedPatientId')
 * @param initial Initial value
 * @param options Optional configuration (urlSync, etc.)
 */
export declare function signal<T extends SignalValue>(key: string, initial: T, options?: SignalOptions): Signal<T>;
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