observedEpochNanos

Epoch-nanosecond timestamp at which the record was observed by the SDK, from the producer's local clock — OTLP's observedTimeUnixNano.

On a queueing capture edge this is the flush instant, not the event instant; a consumer that reads it as event time sees drain cadence rather than when anything happened. Use timestampEpochNanos for that, and fall back to this only when it is null.