/**
 * Return the filenames to prune: everything except the newest `keep` docs by
 * lexicographic-descending order. The `current` (lastHandoff) filename is
 * ALWAYS retained — a belt-and-suspenders invariant so the active handoff can
 * never be deleted, even if it would otherwise fall outside the newest `keep`.
 *
 * Lexicographic-descending order is deterministic and offline: SESSION names
 * carry an ISO date prefix (`SESSION-YYYY-MM-DD[-label].md`), so descending
 * string order is chronological at day granularity, with intra-day label ties
 * broken alphabetically. The returned list preserves that descending order.
 *
 * Pure: no filesystem access, no side effects.
 */
export declare function selectPrunable(filenames: readonly string[], keep: number, current: string): string[];
/**
 * Impure companion to `selectPrunable`: read the handoff `dir`, select the
 * `SESSION-*.md` docs to prune (keeping the newest `retain` plus `current`),
 * `unlink` them, and return the pruned filenames. The caller (run-handoff)
 * invokes this best-effort and swallows any throw — it must never fail a
 * handoff write. Signature matches the injectable `prune` seam.
 */
export declare function pruneHandoffDir(dir: string, retain: number, current: string): Promise<string[]>;
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