The dev mock's Identity/set discarded its payload and Identity/get always returned a static list, so saved identities never round-tripped in local development. Persist create (with mayDelete: true), update, and destroy in place, mirroring handleMailboxSet, so signature edits stick when testing without a real JMAP server. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>