Debug-Prototype-Pollution-Merge-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. A deep merge copies __proto__ keys from input into a target object, changing behavior of later lookups. Identify the mutation bug and fix.

{
  "metrics": {
    "repro": {
      "checks": [
        {
          "contains": [
            "__proto__"
          ]
        },
        {
          "contains": [
            "target object"
          ]
        },
        {
          "contains": [
            "later lookups"
          ]
        },
        {
          "contains": [
            "deep merge"
          ]
        }
      ]
    },
    "hidden": {
      "checks": [
        {
          "contains": [
            "block prototype keys"
          ]
        },
        {
          "contains": [
            "Object.create(null)"
          ]
        },
        {
          "contains": [
            "own properties"
          ]
        }
      ]
    },
    "diagnose": {
      "checks": [
        {
          "contains": [
            "prototype pollution"
          ]
        },
        {
          "contains": [
            "merge"
          ]
        },
        {
          "contains": [
            "mutation"
          ]
        }
      ]
    }
  }
}