Debug-Object-Spread-Shallow-V2

The model receives the prompt (and optional system message). The run uses scorer rubric_json_metrics with the JSON configuration below. Pass/fail and partial credit are determined entirely by that scorer against the model output; no human grading.

Return JSON only with keys diagnosis, fix, tests. An object containing nested arrays is cloned with the spread operator; mutations to the nested arrays in the clone also affect the original object. Identify the shallow copy bug and fix it.

{
  "metrics": {
    "repro": {
      "checks": [
        {
          "contains": [
            "nested"
          ]
        },
        {
          "contains": [
            "spread"
          ]
        },
        {
          "contains": [
            "shared"
          ]
        },
        {
          "contains": [
            "mutation"
          ]
        }
      ]
    },
    "hidden": {
      "checks": [
        {
          "contains": [
            "structuredClone"
          ]
        },
        {
          "contains": [
            "deep copy"
          ]
        },
        {
          "contains": [
            "JSON.parse"
          ]
        }
      ]
    },
    "diagnose": {
      "checks": [
        {
          "contains": [
            "shallow clone"
          ]
        },
        {
          "contains": [
            "nested reference"
          ]
        },
        {
          "contains": [
            "spread operator"
          ]
        }
      ]
    }
  }
}