Exit condition:

{
  "leaveWithGrappleSwing": {
    "blocks": [
      {
        "position": [
          -1,
          5
        ],
        "environment": "water",
        "note": "The closest solid (non-crumbling) Grapple block left of the top door"
      },
      {
        "position": [
          12,
          5
        ],
        "environment": "water",
        "note": "The closest Grapple block right of the top door"
      }
    ]
  }
}

Unlocks doors:

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

Dev note: Other Grapple blocks could be used on the left side, but there's no apparent reason to.