Requires:

{
  "heatFrames": 15
}

Exit condition:

{
  "leaveWithRunway": {
    "length": 7,
    "openEnd": 1
  }
}

Unlocks doors:

{"types":["ammo"],"requires":[]}

Dev note: The blocks respawn, so no need to split this in two runways. While waiting for respawn would take additional heat frames, the spawner makes that more or less inconsequential.