payload property
Sized for the largest response any build can carry: 6168 is Urpsec_RawMeasurement_size. UrpSecSecureMeasurement, the largest response for SEC, IMZ and IMP, needs 1027.
This was previously split into a 1027-byte PUBLIC ONLY variant and a 6168-byte TEST ONLY one. That became inconsistent when measureRaw was made public: UrpSecRawMeasurement and urpSecMeasureRaw ship in the open-source definitions, but an envelope capped at 1027 cannot carry one, so firmware built from those definitions could not emit the response its own schema advertises.
Implementation
@$pb.TagNumber(1)
$core.List<$core.int> get payload => $_getN(0);