DispatchQueue.concurrentPerform + UnsafeRawPointer in Swift 6

Using Swift
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2

It turns out, if we just define the closure before passing it to concurrentPerform it works:

let closure = { (row: Int) in
    let part1 = someData[row]
    let part2 = moreData[row]
    buffer[row] = simd_float4(lowHalf: part1, highHalf: part2)
}

DispatchQueue.concurrentPerform(iterations: capacity, execute: closure)

My guess is that closure is not Sendable here, so the compiler won't complain about the buffer access. And concurrentPerform is marked with @preconcurrency, so passing a non-sendable closure is also ok. But it feels wrong...

Is there a better pattern for this kind of work?