/**
 * Active Sessions Registry (GIT-19)
 *
 * CRUD operations for .gitmem/active-sessions.json — the multi-session
 * registry that tracks all running MCP server sessions.
 *
 * Key design decisions:
 * - Atomic writes (write-temp-rename) because multiple processes may
 *   register/unregister concurrently.
 * - Sync I/O to match codebase convention (fs.writeFileSync etc).
 * - Graceful degradation: corrupted registry = start fresh.
 */
import type { ActiveSessionEntry } from "../types/index.js";
/**
 * A cheap fingerprint of the registry's current state (GIT-51).
 *
 * Session recovery needs to know whether it is worth retrying. The registry is
 * written by OTHER processes — notably the SessionStart hook, which runs as its
 * own CLI process (scar 55d1bccd) — so "I already failed to recover" is only
 * valid until someone else touches the file.
 *
 * Returns null when neither the registry nor the sessions directory exists,
 * which is itself a stable state worth caching against.
 *
 * GIT-89: covers the sessions directory as well as the registry. Identity now
 * resolves from sessions/<id>/session.json, so a fingerprint that watched only
 * active-sessions.json would keep the "already failed" latch closed over a
 * session that had since appeared on disk — reintroducing the permanent
 * fail-closed behaviour the fingerprint was introduced to prevent.
 */
export declare function getRegistryFingerprint(): number | null;
/**
 * Register a new session in the active-sessions registry.
 * Idempotent: re-registering the same session_id replaces the entry.
 * Returns session IDs that were displaced (different session_id, same hostname+pid).
 */
export declare function registerSession(entry: ActiveSessionEntry): string[];
/**
 * Unregister a session from the active-sessions registry.
 * Returns true if the session was found and removed.
 */
export declare function unregisterSession(sessionId: string): boolean;
/**
 * List all active sessions from the registry.
 */
export declare function listActiveSessions(): ActiveSessionEntry[];
/**
 * Find a session by hostname and PID.
 * Used by session_start to detect if this process already has a registered session.
 */
export declare function findSessionByHostPid(hostname: string, pid: number): ActiveSessionEntry | null;
/**
 * Find a session by session_id.
 */
export declare function findSessionById(sessionId: string): ActiveSessionEntry | null;
export declare function findResumableSessionOnDisk(): ActiveSessionEntry | null;
/**
 * Prune stale sessions from the registry (GIT-22 enhanced).
 *
 * A session is stale if:
 * 1. Its started_at is older than 24 hours, OR
 * 2. Its per-session directory/session.json is missing (orphaned registry entry)
 *
 * GIT-51: A dead PID is NOT on its own grounds for pruning. The MCP server
 * restarting mid-session leaves exactly that signature, and deleting the entry
 * (and its session directory) destroys a live session's state. Dead-PID entries
 * are left for adoptSessionForCurrentProcess() to recover, and fall out on the
 * 24h age path if nobody claims them.
 *
 * Also cleans up per-session directories for pruned sessions,
 * and removes orphaned session directories with no registry entry.
 * Returns the number of sessions pruned.
 */
export declare function pruneStale(): number;
/**
 * GIT-23: Migrate from old active-session.json (singular) to new multi-session format.
 *
 * Runs once per process. If old file exists and new registry does not:
 * 1. Read old file
 * 2. Create per-session directory with session.json
 * 3. Create active-sessions.json registry with single entry
 * 4. Rename old file to active-session.json.migrated (backup)
 *
 * Idempotent: skips if new registry already exists or old file is absent.
 */
export declare function migrateFromLegacy(): boolean;
/**
 * Reset migration flag (for testing only).
 */
export declare function resetMigrationFlag(): void;
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