  High contrast imaging (HCI) systems rely on active wavefront control (WFC) to
deliver deep raw contrast in the focal plane, and on calibration techniques to
further enhance contrast by identifying planet light within the residual
speckle halo. Both functions can be combined in an HCI system and we discuss a
path toward designing HCI systems capable of calibrating residual starlight at
the fundamental contrast limit imposed by photon noise. We highlight the value
of deploying multiple high-efficiency wavefront sensors (WFSs) covering a wide
spectral range and spanning multiple optical locations. We show how their
combined information can be leveraged to simultaneously improve WFS sensitivity
and residual starlight calibration, ideally making it impossible for an image
plane speckle to hide from WFS telemetry. We demonstrate residual starlight
calibration in the laboratory and on-sky, using both a coronagraphic setup, and
a nulling spectro-interferometer. In both case, we show that bright starlight
can calibrate residual starlight.
