/**
* Resolves timezone parameter according to project convention:
* - undefined → system's local timezone (defaultTimezone)
* - "" (empty string) → UTC
* - Any other string → that specific IANA timezone
*
* This utility ensures consistent timezone resolution across all tools.
* It does not validate the timezone string - that's handled elsewhere.
*/
export function resolveTimezone(timezone: string | undefined, defaultTimezone: string): string {
if (timezone === '') return 'UTC';
return timezone ?? defaultTimezone;
}