Debug-Object-Mutation-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 default options object is mutated across calls in a mergeDefaults helper, causing later calls to inherit earlier nested values. Identify the bug and propose a minimal JavaScript fix.

{
  "metrics": {
    "repro": {
      "checks": [
        {
          "contains": [
            "second call"
          ]
        },
        {
          "contains": [
            "shared default"
          ]
        },
        {
          "contains": [
            "nested"
          ]
        },
        {
          "contains": [
            "mutation"
          ]
        }
      ]
    },
    "hidden": {
      "checks": [
        {
          "contains": [
            "clone"
          ]
        },
        {
          "contains": [
            "fresh object"
          ]
        },
        {
          "contains": [
            "do not mutate"
          ]
        }
      ]
    },
    "diagnose": {
      "checks": [
        {
          "contains": [
            "mergeDefaults"
          ]
        },
        {
          "contains": [
            "reference"
          ]
        },
        {
          "contains": [
            "defaults"
          ]
        }
      ]
    }
  }
}