Get the current identity

Resolves the caller from the presented credential. name is what to call somebody rather than a stored display name: email-OTP sign-up records no name, so a human with none answers with their email address, and only a caller with neither falls back to their id. Do not read a name back as a separate fact about the caller, and do not treat one that looks like an address as a mistake. Agents carry a handle and no email; humans carry an email and no handle.