Stable-cell mounting

{
  "styles": {
    "ground": {
      "generator": "tiles",
      "outDir": "assets/tiles/src",
      "mount": {
        "base": "assets/tiles/spritesheet.png",
        "cellWidth": 32,
        "cellHeight": 32,
        "out": "assets/tiles/spritesheet.png"
      }
    }
  },
  "assets": {
    "rough_grass": {
      "prompt": "unmown dark grass",
      "cell": [6, 2],
      "outputRole": "tile-03"
    }
  }
}

base is optional; omission starts from transparency. out may equal base. Assets without cell are not mounted. Two assets cannot own one cell. A sprite larger than its cell is reported and skipped rather than cropped. source lets a remapped or hand-edited committed file replace generated input without losing the declarative placement; sourceByStyle does the same for one style. pixelkiln edit manages both for hand edits.