Your seed prase never leaves your browser, yet most of the process happens on the server, vastly improving performance. Single recovery round scans up to 2500 recovery indexes, that should be enough for most wallets. To prevent attack on mint resources, further recovery rounds cost 100 sats, charged using brand new HTTP 402 standard (NUT 24 spec) - pay for api use with an ecash token. Free use then resumes after 15 minutes, based on ip address.