Left panel: time-resolved spectra of the canonical LGRB (solid lines) and SGRB (dashed lines) cocoon models at θ_v = 10^∘. The blue, yellow, and red curves correspond to t_obs = t_5%, t_50%, and t_95%, marking the beginning, midpoint, and end of the T₉₀ interval, respectively. All spectra are quasi-thermal. Right panel: temporal evolutions of the peak energy for the canonical LGRB (solid lines) and SGRB (dashed lines) cocoon models. The blue, red, and green curves correspond to θ_v = 10^∘, 20^∘, and 45^∘, respectively. Circles, squares, and diamonds mark t_obs = t_5%, t_50%, and t_95%, respectively. Open and filled symbols denote the LGRB and SGRB cocoons.