Function require_kind 

pub fn require_kind(
    caixa: &Caixa,
    expected: CaixaKind,
) -> Result<(), KindMismatch>

Predicate: assert that caixa.kind == expected, returning a typed KindMismatch view (carrying Caixa::nome) on rejection. The canonical entry-point every per-kind renderer wraps in its own thiserror Error variant via #[from] — the call site becomes a single caixa_core::require_kind(caixa, CaixaKind::X)?; in place of the prior inline if caixa.kind != CaixaKind::X { return Err(Error::NotAnX(caixa.kind)); } block.

Lifted to a single helper so a future per-kind renderer (caixa-otel, the future per-Aplicacao CR materializer the M3.x roadmap acknowledges, the future per-Supervisor reconciler renderer) gets the same naming-the-offending-caixa diagnostic for free, and a future change to the diagnostic format (e.g. adding a Caixa::versao suffix once multi-version-skew authoring lands) is one edit here, not a coordinated rewrite of every renderer.

Errors

Returns KindMismatch when caixa.kind != expected. The error carries the caixa’s :nome so the diagnostic names the offending caixa.lisp — same shape every renderer’s Error::From<KindMismatch> converts into the renderer’s local error type.