SOAR/HRCam I-band 5σ contrast curve for TOI-789, with the speckle autocorrelation function shown in the inset. No stellar companion is detected; the limit (Δmag ≈ 3.7 at 0﹩\mathop{.}\limits^{{\prime\prime} }﹩5, reaching ≈6.5 at ∼3″) excludes unresolved companions that could be the source of, or dilute, the transit signals. The deeper Gemini-South/Zorro 832 nm limit (Δmag ≈ 6.8 at 0﹩\mathop{.}\limits^{{\prime\prime} }﹩5; Section 2.3) is the contrast constraint adopted in the TRICERATOPS analysis (Section 4.2).