Effect of stellar metallicity control on the C/O dichotomy between hot and warm giant-planet hosts. Left panels: uncontrolled sample. The upper-left panel shows the CDFs of [Fe/H] for hot (orange) and warm (green) giant-planet hosts, with a moderate difference (P = 0.03). The lower-left panel displays C/O vs. [Fe/H], with the adjacent CDF panel showing a significant C/O offset between the two populations (P = 5.7 × 10⁻⁶). Right panels: metallicity-controlled sample after stratified matching. The upper-right panel confirms that the [Fe/H] distributions are now statistically indistinguishable (P = 0.77). The lower-right panel shows that the C/O difference remains highly significant (P = 2.5 × 10⁻⁶), demonstrating that the C/O dichotomy is independent of stellar metallicity.