ChangeKdfRequestModel : Dual-shape request: validation accepts either the legacy
(Bit.Api.Auth.Models.Request.Accounts.ChangeKdfRequestModel.NewMasterPasswordHash,
Bit.Api.Auth.Models.Request.Accounts.ChangeKdfRequestModel.Key) or new
(Bit.Api.Auth.Models.Request.Accounts.ChangeKdfRequestModel.AuthenticationData,
Bit.Api.Auth.Models.Request.Accounts.ChangeKdfRequestModel.UnlockData) payload so the wire
contract can stabilize ahead of caller wiring. PostKdf currently honors only the new shape;
legacy-shape dispatch arrives with ChangeKdfCommand’s dual-path refactor. All legacy fields
are removed in PM-33141.