First look at a performance problem

Something is slow: {{symptom}}. My current guess is {{suspicion}}.

Before I change anything, tell me what to measure and how — the specific numbers
that would confirm or kill that guess. Then list two other explanations that fit
the same symptom, with a cheap check for each.

Do not suggest optimisations yet. If my guess is the obvious one, say what would
make it wrong.

What to fill in

{{symptom}}

What's slow — e.g. the overlay takes ~400ms to appear

{{suspicion}}

Your current suspicion — e.g. SwiftUI rebuilding the whole tree per open