Function endpoint_probe 

pub fn endpoint_probe<W>(
    writer: W,
    shard_endpoints: Arc<Vec<Vec<W::Endpoint>>>,
) -> SinkProbeFn
where
    W: ShardWriter + Clone,

Build a SinkProbeFn that probes every replica of every shard in shard_endpoints (indexed [shard][replica]) via ShardWriter::probe — the readiness loop SinkParts::with_probe expects. Back writer with an independent probe client set, never the insert clients (see SinkParts::probe).