Function endpoint_probe 

pub fn endpoint_probe<W>(
    writer: W,
    shard_endpoints: Arc<Vec<Vec<<W as ShardWriter>::Endpoint>>>,
) -> Box<dyn Fn() -> Pin<Box<dyn Future<Output = Result<(), SinkError>> + Send>> + Sync + Send>
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).