Function patch_runs 

fn patch_runs(diff: &StateDiff, scan: &Scan) -> Patched

Rebuilds one diff’s runs winner-ward and subtracts the collision the patch creates.

The runs are mapped independently, so a ghost in one run whose winner sits in the other patches both to one entry, and applying added before removed would then erase the state key. Subtracting the intersection from removed is exact in both orientations: the row meant the key holds this event before the patch, and it still does after. shrunk is taken first, keeping its meaning to duplicates converging inside one run.