Debug-Stream-Backpressure-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 stream writer ignores write() returning false and continues enqueueing chunks until memory spikes and the process crashes. Identify the bug and fix.

{
  "metrics": {
    "repro": {
      "checks": [
        {
          "contains": [
            "write"
          ]
        },
        {
          "contains": [
            "false"
          ]
        },
        {
          "contains": [
            "memory"
          ]
        },
        {
          "contains": [
            "chunks"
          ]
        }
      ]
    },
    "hidden": {
      "checks": [
        {
          "contains": [
            "drain"
          ]
        },
        {
          "contains": [
            "backpressure"
          ]
        },
        {
          "contains": [
            "await"
          ]
        }
      ]
    },
    "diagnose": {
      "checks": [
        {
          "contains": [
            "stream writer"
          ]
        },
        {
          "contains": [
            "enqueue"
          ]
        },
        {
          "contains": [
            "crash"
          ]
        }
      ]
    }
  }
}