F# retry with capped exponential backoff and jitter

open System
open System.Threading

let retry (attempts: int) (op: unit -> 'T) : 'T =
    if attempts < 1 then invalidArg "attempts" "must be at least 1"
    let rnd = Random()
    let mutable result : 'T option = None
    let mutable attempt = 0
    while result.IsNone do
        try
            result <- Some(op ())
        with _ when attempt < attempts - 1 ->
            let delay = min 1000.0 (100.0 * 2.0 ** float attempt)
            Thread.Sleep(int (delay + delay * 0.5 * rnd.NextDouble()))
            attempt <- attempt + 1
    result.Value