Deep HST photometry of the white-dwarf cooling sequence in globular cluster NGC 6397, identifying a truncation in the luminosity function corresponding to the coolest (oldest) white dwarfs and deriving a cluster age of 11.47 ± 0.47 Gyr from white-dwarf cooling models — independent of main-sequence turnoff dating. Directly evidences that white dwarfs, as a class, persist and cool undisturbed for >11 Gyr, i.e. essentially the age of the Galaxy. relevance_note: Primary empirical evidence for the specific Gyr-scale survival timescale (not just existence) that the white-dwarf-survival bound in Premise B needs to be quantitatively meaningful.