MordaFace

I'm trying to write a script to control a worker drone. This drone will interact with plants on specific coordinates that are being fed to him by mainframe via wireless modem. I've planned to have those commands:
1. Add/remove new coordinates.
2. Print out all registered coordinates.
3. Finish the job, return to charger and wait for further commands. 
4. ...

The initial solution included using two threads: a worker thread that executes requested and routine actions and a controller thread that listens for new modem messages, updates drone status and generates responses for the mainframe. The problem is - drones have no access to Thread API. I believe there should be a simple solution for this task but I don't see any suitable way to provide such level of responsiveness without proper threading.

Rough example for drone :
 

...
thread.waitForAny({
  thread.create(function()  -- Worker
    while true do
      if state == "work" then
        for _, pos in pairs(locations) do
          moveto(pos)
          dostuff()
          if state ~= "work" then break end
        end
      elseif state == "stop" then
        sleep(5)
      end
    end
  end),
  thread.create(function() -- Controller
    while true do
      local message = table.pack(computer.pullSignal())
      if message[1] == "modem_message" then
        local command = serialization.deserialize(message[5])
        if command.text == "stop" then 
          state = "stop" 
        elseif command.text == "resume" then
          state = "work"
      end
    end
}})

I am sure somebody already did this kind of stuff on their server, I just can't come up with anything effective and simple without surpassing the 4KiB threshold. Do you have any suggestions?