Function apply_marker_ack 

pub fn apply_marker_ack<EF, V, LF>(
    presented_identity: PresentedIdentity<'_, EF, V, LF>,
    binding: &BindingState,
    receiving_binding_epoch: BindingEpoch,
    request: &MarkerAck,
    marker_state: &MarkerProofState,
) -> MarkerAckDecision

Applies the complete zero-debt marker-ack selector.

Existing shared lookup enforces retired, unknown, stale-authority, and exact-binding precedence. Only authorized requests enter marker proof. The proof snapshot’s cursor and proof epoch are derived here from the verified member and binding; callers provide only the remaining durable marker facts. An exact accepted marker at the member cursor returns AckNoOp. Every other refusal is nonmutating, while an exact delivered marker returns a replay-safe MarkerAckCommit.