  We study the ratio of neutrino-proton elastic scattering to inverse beta
decay event counts, measurable in a scintillation detector like JUNO, as a key
observable for identifying the explosion mechanism of a galactic core-collapse
supernova. If the supernova is not powered by the core but rather, e.g., by
collapse-induced thermonuclear explosion, then a prolonged period of
accretion-dominated neutrino luminosity is predicted. Using 1D numerical
simulations, we show that the distinct resulting flavour composition of the
neutrino burst can be tested in JUNO with high significance, overcoming
theoretical uncertainties in the progenitor star profile and equation of state.
