• Pre-Pitting Segmentation Using K-Means Clustering To explore whether specific regions of the passive film exhibited distinct properties before pitting, we performed K-Means clustering on the arrays from one frame before UMAP separation occurred. This step allowed segmentation of the sample surface into two categories based on the temporal intensity evolution of pixels. The mechanistic interpretation of these clusters, provided in the main text, suggests that they correspond to differences in the passive film's local stability. A silhouette plot SI5-1 was used to assess clustering quality.