Consume fidelity evidence, not re-proofs #429

The multi-prover plan's value was the disagreement signal between
independent formalisations, which autoformal-fidelity states precisely
(two target standpoints; agreement = identical partitions; convergence is
evidence only under independence). Ask: echidna ingests fibre coverage,
round-trip and cross-prover agreement from one kernel (Agda) plus
independent standpoints, rather than N copies of each proof.

Filed from the 2026-10-12 family session; see nextgen-typing docs/TYPE-CONNECTIONS.adoc for the connection statuses.