Which two observational signals are capable of providing scientists with a near-instantaneous look at the core's mechanical violence preceding the visible light?
Gravitational waves and neutrino signatures
Modern astrophysics has opened new avenues for studying the core-collapse mechanism before the visible explosion arrives. The immense mechanical violence associated with the collapse and bounce generates ripples in spacetime known as gravitational waves. These waves offer a direct, near-instantaneous measurement of the internal mechanics. Furthermore, the same process of inverse beta decay that powers the shockwave also releases an unparalleled burst of neutrinos. Detecting these tell-tale neutrino signatures gives observatories crucial lead time, allowing telescopes to be pointed toward the dying star moments before the electromagnetic radiation (the visible light) from the shockwave breaks out through the surface.

#Videos
A Detailed Breakdown of Core Collapse Supernovae