observations

Per-replication observations for the given experimentName / responseName pair. Returns null when the experiment did not record that response, when the experiment is unknown, or when no per-replication data is available (counters that record only an end-of-replication count are surfaced as last_value and still return a one-value-per-rep array). Empty array is reserved for "experiment recorded the response but produced no values" — vanishingly rare in practice but worth distinguishing from "no recording at all".