Astrometric Detection Budgets: Planet Signatures Against Gaia-Class Angular Precision

This study computes a detection budget for a clearly bounded question: What angular wobble does a planet induce on its host star, how does that signature compare with Gaia-class per-epoch precision as a function of magnitude, and which planet population does the comparison leave accessible? Jupiter at 5 au and 10 pc: 477 microarcseconds. At 25 pc: 191 microarcseconds. Earth at 1 au and 10 pc: 0.30 microarcseconds, a factor 0.009 of the G = 13 threshold. Mission-averaged thresholds are 21 microarcseconds at G = 10 and 251 at G = 18. All values are computed from published anchor values and stated assumptions by a deposited script; the study is simulated and computed throughout, not measured. Gaia-class astrometry opens the wide-orbit giant population with true masses, while terrestrial signatures fall two orders of magnitude below its floor.