/**
 * Storage pre-flight checks.
 *
 * Detects when legacy JSON data exists but has not been migrated to SQLite,
 * and provides actionable diagnostics for users upgrading from V1.
 *
 * Per ADR-006, SQLite is the only supported storage engine.
 *
 * @task T4699
 * @task T5305
 */
/** Pre-flight check result. */
export interface PreflightResult {
    /** Whether a storage migration is needed. */
    migrationNeeded: boolean;
    /** Current detected storage engine. Always 'sqlite' or 'none'. */
    currentEngine: 'sqlite' | 'none';
    /** Human-readable summary of what was detected. */
    summary: string;
    /** Actionable fix command. */
    fix: string | null;
    /** Detailed diagnostics. */
    details: {
        todoJsonExists: boolean;
        todoJsonTaskCount: number;
        archiveJsonExists: boolean;
        archiveJsonTaskCount: number;
        sessionsJsonExists: boolean;
        sessionsJsonCount: number;
        tasksDbExists: boolean;
        tasksDbSize: number;
        configEngine: string | null;
    };
}
/**
 * Check whether legacy JSON data needs to be migrated to SQLite.
 *
 * Returns a diagnostic result that callers can use to warn users.
 * This function is read-only and never modifies any files.
 */
export declare function checkStorageMigration(cwd?: string): PreflightResult;
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