/**
 * Pure receipt-chain LINKAGE verifier.
 *
 * Checks only that each token's signed body `prev` field matches the predecessor commitment
 * (literal 'null' for a root, or 'sha256:'+hex(sha256(previous_token)) for a link). Does NOT
 * verify Ed25519 signatures, expiry, keys, or authorization — those live on the verify-receipt
 * path. Linkage ≠ authenticity.
 *
 * The composition / guard MUST NOT call this over a package-held chain and report the result as
 * product truth; a consumer re-runs this (and signature verify) on an export they hold.
 */
/** Literal stored in the receipt body when the issuer was given no previous receipt. */
export declare const RECEIPT_PREV_NULL = "null";
export type ReceiptChainLinkageReason = 'malformed_token' | 'broken_link' | 'unexpected_predecessor';
export type ReceiptChainLinkageResult = {
    ok: true;
    /** Number of tokens examined (0 for an empty list — vacuously linked). */
    length: number;
} | {
    ok: false;
    length: number;
    /** 0-based index of the token that failed the check. */
    failedAt: number;
    reason: ReceiptChainLinkageReason;
    /** What the verifier expected in body.prev (when known). */
    expected?: string;
    /** What body.prev actually contained (when parsed). */
    actual?: string;
};
/**
 * sha256 hex digest of a prior receipt token, in the issuer's prev-slot form:
 * `sha256:` + hex (matches server chain-attestation issueReceipt).
 */
export declare function previousReceiptCommitment(previousToken: string): string;
/**
 * Decode the JSON body of a chain receipt token (`base64url(body).base64url(sig)`).
 * Returns null if the token is not two segments or the body is not JSON with a string `prev`.
 */
export declare function decodeReceiptBodyPrev(token: string): {
    prev: string;
} | null;
/**
 * Verify predecessor-hash LINKAGE over an ordered list of receipt tokens.
 *
 * - Empty list → ok (vacuous).
 * - tokens[0] must have prev === 'null' (root of this presented sequence).
 * - tokens[i] must have prev === previousReceiptCommitment(tokens[i-1]).
 *
 * Does not contact the network or consult a clock.
 */
export declare function verifyReceiptChainLinkage(tokens: readonly string[]): ReceiptChainLinkageResult;
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