Debug-Db-Transaction-Isolation-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. Two concurrent transactions each read a shared counter row, each adds 1 to the value, and each writes back; under Read Committed isolation both read the same initial value so the net increment is 1 instead of 2. Identify the lost-update anomaly and fix it.

{
  "metrics": {
    "repro": {
      "checks": [
        {
          "contains": [
            "concurrent transactions"
          ]
        },
        {
          "contains": [
            "Read Committed"
          ]
        },
        {
          "contains": [
            "counter"
          ]
        },
        {
          "contains": [
            "lost update"
          ]
        }
      ]
    },
    "hidden": {
      "checks": [
        {
          "contains": [
            "SELECT FOR UPDATE"
          ]
        },
        {
          "contains": [
            "Serializable"
          ]
        },
        {
          "contains": [
            "optimistic locking"
          ]
        }
      ]
    },
    "diagnose": {
      "checks": [
        {
          "contains": [
            "lost-update anomaly"
          ]
        },
        {
          "contains": [
            "same initial value"
          ]
        },
        {
          "contains": [
            "isolation level"
          ]
        }
      ]
    }
  }
}