/**
 * push/subscription-validation.ts
 *
 * The ONE place a push subscription's endpoint and key material are judged
 * well-formed. Two callers share it and must never disagree:
 *
 *  - Registration (`routes/push.ts`, `routes/pairing-handoff.ts`,
 *    `PushSubscriptionStore.reconcile`), junk is refused with a plain reason at
 *    the moment it is offered, so a record that could never receive a push is
 *    never written to disk in the first place.
 *  - Delivery (`push/encryption.ts`), the same predicates, with the same
 *    wording, guard the encryption path.
 *
 * Sharing the predicates is the point: before this module, registration checked
 * only that the strings were non-empty while delivery checked the byte lengths,
 * so `p256dh: "not-base64!!!!"` was accepted at 200 and only failed weeks later
 * as a delivery error. The two now fail on exactly the same inputs with exactly
 * the same message.
 */
/** RFC 8291: the receiver's public key is an uncompressed P-256 point. */
export declare const P256DH_POINT_BYTES = 65;
/** RFC 8291: the receiver's authentication secret is 16 bytes. */
export declare const AUTH_SECRET_BYTES = 16;
/**
 * Upper bound on a stored endpoint. Real push endpoints (FCM, Mozilla, WNS) are
 * a few hundred characters; anything past this is not an endpoint the daemon
 * should be persisting, and an unbounded one is a way to grow the store on disk
 * without registering anything usable.
 */
export declare const MAX_PUSH_ENDPOINT_LENGTH = 2048;
/**
 * The delivery path's wording, kept verbatim so registration and delivery
 * report the same failure in the same words.
 */
export declare const P256DH_INVALID_MESSAGE = "Push subscription p256dh key is not a 65-byte uncompressed P-256 point";
export declare const AUTH_SECRET_INVALID_MESSAGE = "Push subscription auth secret is not 16 bytes";
/** The field a validation problem belongs to, as the caller names it on the wire. */
export type PushSubscriptionField = 'endpoint' | 'keys.p256dh' | 'keys.auth';
/** A refused subscription: which field, and why, in plain language. */
export interface PushSubscriptionProblem {
    readonly field: PushSubscriptionField;
    readonly reason: string;
}
/** Thrown when a subscription is offered for storage with unusable content. */
export declare class PushSubscriptionValidationError extends Error {
    readonly field: PushSubscriptionField;
    constructor(problem: PushSubscriptionProblem);
}
/** Why this p256dh cannot be used, or null when it is a valid point. */
export declare function describeP256dhProblem(value: unknown): string | null;
/** Why this auth secret cannot be used, or null when it is 16 bytes. */
export declare function describeAuthSecretProblem(value: unknown): string | null;
/** Why this endpoint cannot be used, or null when it is a bounded http(s) URL. */
export declare function describeEndpointProblem(value: unknown): string | null;
/** The structural slice validated, the wire shape of a subscription offer. */
export interface PushSubscriptionCandidate {
    readonly endpoint: unknown;
    readonly keys?: {
        readonly p256dh?: unknown;
        readonly auth?: unknown;
    } | undefined;
}
/**
 * The first problem with a candidate subscription, or null when every field is
 * usable. Endpoint first, then the key material, so the caller reports the most
 * structural failure rather than a downstream one.
 */
export declare function describeSubscriptionProblem(candidate: PushSubscriptionCandidate): PushSubscriptionProblem | null;
/** Throwing form of {@link describeSubscriptionProblem}. */
export declare function assertUsableSubscription(candidate: PushSubscriptionCandidate): void;
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