Constant TEMPO_BROWSER_WEBAUTHN_DATA_SIZE 

const TEMPO_BROWSER_WEBAUTHN_DATA_SIZE: u16 = 1_400;

Viem’s Tempo formatter uses a 1,400-byte WebAuthn placeholder when the signature is not yet available. Tempo RPC encodes that size as a two-byte big-endian keyData value (0x0578).

See https://github.com/wevm/viem/blob/61a40ec943652a09ee6622e2349c5fedca97ed5e/src/tempo/Formatters.ts#L148-L159.