/**
 * Converts a **keep-last** window in **hours** (fractional allowed, e.g. `0.5` → 30 minutes)
 * into the **`olderThanMs`** value used by soft purge (`purgeOldRecords` / `cleanKeepLastHours`).
 *
 * Rows with `startTime < Date.now() - olderThanMs` are purged; rows inside the window are kept.
 * **`0` hours** ⇒ `olderThanMs === 0` ⇒ everything strictly before “now” is purged (typical **clean-all**).
 */
export declare function keepLastHoursToPurgeOlderThanMs(hours: number): number;
/** Lower bound for `startTime` when exporting “last *hours*” (`Date.now() - ms`). */
export declare function keepLastHoursToExportStartTimeMin(hours: number): number;
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