Construction process of the temporal variation of the Sun-as-a-star contrast profile, C(λ, t) (Eq. (4)), with a resolution equivalent to HARPS-N, derived from high-resolution SST observations of the X9.3 flare, listed as Event 1 in Table A.1, for Hα (top row) and Ca II K (bottom row). Each panel presents the contrast profile relative to quiet-Sun profiles (black curves). Color bars denote the values of C(λ, t). Left column: Sun-as-a-star contrast profiles generated using the NESSI code. Middle column: Same as the left column but resampled to the HARPS-N temporal resolution of 5 minutes and degraded by adding normally distributed noise with a standard deviation estimated from the wings of line profiles observed by HARPS-N. Right column: Contrast profiles of Hα and Ca II K reconstructed from HARPS-N observations of Event 1, shown also in Fig. 4.