Results from the validation retrieval on the 3–20 μm, R = 1000, and photon noise S/N = 50 Venus-twin spectrum (opaque H₂SO₄ clouds) using the opaque H₂SO₄ cloud forward model. Top left: Corner plot of the posterior distribution of the forward model parameters. Here, L(·) stands for log₁₀(·). We derived the equilibrium temperature T_eq and the Bond albedo A_B from the other posteriors (see Appendix B). The dotted black lines indicate the true values. In the 1D posteriors, we show the 16th, 50th, and 84th percentiles as black dashed lines. Top right: P–T profile residuals relative to the retrieved median P–T profile. Color-shaded regions indicate percentiles of the retrieved P–T profiles. The gray shaded regions indicate percentiles of the retrieved cloud-top pressure. The solid black line, the orange circular marker, and the red square marker represent the true Venus-twin P–T profile relative to the median retrieved P–T profile. In the inset figure, we plot the 2D P₀-T₀ posterior. Bottom: Residuals of the spectra corresponding to the retrieved posteriors relative to the Venus-twin input. Color-shaded areas represent different quantiles of the residuals. The gray area marks the 1σ photon noise level.