Function decide_nonzero_debt_ack_operation 

pub fn decide_nonzero_debt_ack_operation(
    conversation: ParticipantConversation,
    commit: Box<NonzeroParticipantAckCommit>,
) -> AggregateOperationDecision<Box<NonzeroParticipantAckCommit>>

Selects the aggregate NonzeroDebtAck event for one consumed ack commit.

Fix 2’s per-participant cursor-fact accounting rides with the consumed commit: the event body’s (participant, through_seq) pair is the exact (participant_index, boundary) cursor-fact key recorded in the commit’s resulting episode, which returns intact through the barrier for the same durable transaction as the event append.