Function reassignment_action 

pub fn reassignment_action(
    completion_ready: bool,
    leader_removed: bool,
    eligible_handoffs: &[bool],
) -> ReassignmentAction

Wait until the reassignment may complete, hand leadership to the first eligible target, or complete while the existing leader remains in the target assignment.

completion_ready is Kafka’s PartitionReassignmentReplicas .maybeCompleteReassignment predicate: every adding replica is in the ISR, and a replication factor decrease does not shrink the ISR. The host evaluates it, so a handoff, like a completion, never runs ahead of it.