Debug-Date-Month-Index-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 date formatter creates new Date(year, month, day) using a one-based month from input, shifting all displayed months forward. Identify the bug and fix.

{
  "metrics": {
    "repro": {
      "checks": [
        {
          "contains": [
            "one-based"
          ]
        },
        {
          "contains": [
            "month"
          ]
        },
        {
          "contains": [
            "shift"
          ]
        },
        {
          "contains": [
            "Date"
          ]
        }
      ]
    },
    "hidden": {
      "checks": [
        {
          "contains": [
            "subtract 1"
          ]
        },
        {
          "contains": [
            "UTC"
          ]
        },
        {
          "contains": [
            "test January"
          ]
        }
      ]
    },
    "diagnose": {
      "checks": [
        {
          "contains": [
            "month index"
          ]
        },
        {
          "contains": [
            "formatter"
          ]
        },
        {
          "contains": [
            "new Date"
          ]
        }
      ]
    }
  }
}