example.kt

ctx.upstream().transact {
  post(..., 10.second)
  post(...)
}

file.kt

suspend fun Context.post(msg: Message, ts: TimeSpan? = null) {
  withTimeoutOrNull(ts ?? 5.second) {
    post(msg)
  }
}

suspend fun Context.transact(transaction: suspend Context.() => Unit) {
  transaction(this)
}