This type is intentionally sealed: the fields are private and there is no
public constructor (no __mint, no doc-hidden escape, no feature-gated
test constructor — Cargo feature unification would make those unsound). The
only sound seal is same-crate construction, so the only way any code —
including transports and authorization policies — can obtain an
AuthenticatedPrincipal is through kernel_authenticate, which verifies
a credential against a registered provider first. This guards against
accidental construction and, combined with enforce_dispatch’s
route-binding, against cross-provider principal spoofing. A hostile actor
editing this crate itself is the only remaining spoofing vector, and that
is a review-level concern, not a type-system one.