The evolution of the proton energy spectrum on 2023 March 13 observed by PSP/IS⊙IS EPI-Lo (ChanP, filled symbols) and EPI-Hi (LETA and HETA, open symbols). Black, red, and orange symbols correspond to the all-directions, sunward-looking (anti-sunward-streaming), and anti-sunward-looking (sunward-streaming) aperture averages, respectively. Top row (panels (a)–(d)): 15 minute averaged spectra at four representative times well before the shock. Bottom row (panels (e)–(h)): 1 minute averaged spectra in the 4 minutes immediately around the shock arrival at 07:13 UT (panels (e)–(g) upstream, panel (h) downstream). In every panel, the red-dashed line marks the asymptotic strong-shock DSA reference j(E) ∝ E⁻¹; the gray solid line marks the steeper reference power law j(E) ∝ E^−2.7.