title: Not getting callback after task reservation fails
body: <p>I'm using the Twilio TaskRouter. A call comes into our number, Twilio makes an API call to our incoming call endpoint. I send the following response:</p>
  
  <pre><code>&lt;Response&gt;
      &lt;Say voice="woman"&gt;Thank you for calling&lt;/Say&gt;
      &lt;Enqueue waitUrl="/Call/HoldMusic" workflowSid="WW..."/&gt;
  &lt;/Response&gt;
  </code></pre>
  
  <p>The call is successfully enqueued and my workflow kicks off. I get the workflow assignment callback and respond with the following JSON:</p>
  
  <pre><code>{
    "instruction": "dequeue",
    "to": "+18885551213",
    "timeout": 10,
    "status_callback_url": "/Workflow/Changed",
    "status_callback_events": "initiated,ringing,answered,completed",
    "from": "+18885551212"
  }
  </code></pre>
  
  <p>The outbound call is successfully made to my "to" number. If I accept the call, I get the reservation.accepted event to my task router callback endpoint. If I don't accept the call (let it timeout), I don't get a notification. Because I don't get a notification the dequeue failed, I can't cancel the reservation and have the call ring down through the queue.</p>
  
  <p>I also changed the workflow assignment callback to return a "call" instruction and set the "status_callback_url" but again I only receive a callback if the call is answered, not if the call times out.</p>
  
  <p>Is there something I'm doing wrong, or something fundamental I'm not understanding?</p>