Suave userData persisting with keep-alive

Program.fs

open Suave
open Suave.Filters
open Suave.Operators
open System

module View =
  let page (data : Map<string, obj>) =
    match data |> Map.tryFind "messages" with
    | Some x ->
        x :?> string list |> List.reduce (+)
    | _ -> ""

let readUserState ctx key : 'value =
  ctx.userState |> Map.tryFind key |> Option.map (fun x -> x :?> 'value) |> Option.get

let addUserMessage (message : string) : WebPart =
  context (fun ctx ->
    let read = readUserState ctx
    let existing =
      match ctx.userState |> Map.tryFind "messages" with
      | Some msgs ->
          read "messages"
      | _ ->
          []
    Writers.setUserData "messages" (message :: existing))

let app =
  choose [
    path "/"
      >=> addUserMessage "Message One"
      >=> addUserMessage "Message Two"
      >=> context (fun ctx -> Successful.OK (View.page ctx.userState))
      //>=> Writers.unsetUserData "messages"
    ]

[<EntryPoint>]
let main argv =
    Web.startWebServer Web.defaultConfig app
    0

test-suave.fsproj

<Project Sdk="FSharp.NET.Sdk;Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>netcoreapp1.1</TargetFramework>
  </PropertyGroup>

  <ItemGroup>
    <Compile Include="Program.fs" />
  </ItemGroup>

  <ItemGroup>
    <PackageReference Include="FSharp.Core" Version="4.1.*" />
    <PackageReference Include="FSharp.NET.Sdk" Version="1.0.*" PrivateAssets="All" />
    <PackageReference Include="Suave" Version="2.1.0" />
  </ItemGroup>

</Project>