/**
 * Persistent IDLE watermarks.
 *
 * The watcher reports a message once, by remembering the highest UID it has
 * seen per account and folder. Holding that only in memory meant every fresh
 * connection re-baselined to the server's current UIDNEXT, so anything that
 * arrived while the process was down — or during a reconnect — was skipped
 * silently: no notification, no hook, no event.
 *
 * Same read/write/lock shape as verification-state.ts, with one addition that
 * matters more here: a watermark is only meaningful against the UIDVALIDITY it
 * was recorded under. If the server renumbers a mailbox, the stored UID points
 * at an unrelated message, so the pair is stored and compared together.
 */
export interface Watermark {
    /** UIDVALIDITY the UID below was observed under, as a decimal string. */
    uidValidity: string;
    lastSeenUid: number;
    updatedAt: string;
}
/** The stored watermark for this account/folder, if any. */
export declare function readWatermark(account: string, folder: string): Promise<Watermark | undefined>;
/** Record the highest UID reported for this account/folder. */
export declare function writeWatermark(account: string, folder: string, uidValidity: string, lastSeenUid: number): Promise<void>;
/**
 * Decide where a newly connected IDLE session should resume from.
 *
 * `uidNext - 1` is the "everything already here is old news" baseline, and it
 * is the right answer only when there is nothing better: the first time a
 * folder is watched, or when the mailbox has been renumbered. Otherwise resume
 * from the highest UID already reported, so the gap left by a restart or a
 * reconnect is reported rather than skipped.
 *
 * The in-memory value wins ties because it is never older than the file, and
 * one that has run ahead of UIDNEXT (a renumbered mailbox the UIDVALIDITY
 * check somehow missed) falls back to the baseline rather than going mute.
 */
export declare function resolveBaselineUid(opts: {
    inMemoryLastSeenUid: number;
    stored: Watermark | undefined;
    uidValidity: string;
    uidNext: number;
}): number;
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