LoAF API pinned a 220ms INP to one script

LoAF API pinned a 220ms INP to one script
INP tells you the duration but not the cause; the Long Animation Frames API names the script.
— A 220ms interaction logged in field RUM with no obvious source
— LoAF attribution showed a single scripts entry: a 190ms style recalc triggered by a class toggle on 4,000 DOM nodes
— Scoped the class change to the 12 visible nodes: recalc 190ms -> 9ms
— INP p75 230ms -> 120ms; the rest of the budget was input delay we couldn't touch
Takeaway: use LoAF attribution — INP duration without the cause is unfixable.