The requirement of electroweak naturalness in simple supersymmetric models
motivates the existence of a cluster of four light higgsinos with
mass 100-300 GeV, the lighter the better. While such light compressed
spectra may be challenging to observe at LHC, future e+e- colliders with
sqrt(s) > 2m(higgsino) would serve as both a SUSY discovery machine and a
precision microscope.

We study higgsino pair production signatures at the ILC based on full,
Geant4-based simulation of the ILD detector concept.
We examine several benchmark scenarios that may or may not be accessible
to HL-LHC searches, with mass differences between the higgsino states
between 20 and 4 GeV. Assuming sqrt(s)= 500 GeV and 1000 fb^-1 of integrated
luminosity, the individual higgsino masses can be measured to 1-2% precision
in case of the larger mass diff?erences, and still at the level of 5% for the
smallest mass difference case. The higgsino mass splittings are sensitive to
the electroweak gaugino masses and can allow extraction of gaugino masses
to ? 3 - 20% (depending on the model).
Extrapolation of gaugino masses via renormalization group running can test
the hypothesis of gaugino mass uni?cation. We also examine a case with
natural generalized mirage mediation where the uni?cation of gaugino masses
at an intermediate scale apparently gives rise to a natural SUSY spectrum
somewhat beyond the reach of HL-LHC.