{
  "id": "distributed-eval-farm",
  "title": "Distributed Eval Farm Coordinator",
  "level": 5,
  "levelName": "Frontier",
  "tagline": "Partition cases, lease shards and aggregate bounded concurrent workers.",
  "summary": "Build a persistent same-host evaluation coordinator that partitions recorded predictions, leases shards to real worker processes, fences stale completions and retains dataset-bound receipts.",
  "usefulFor": [
    "Resume interrupted batch evaluations with exact dataset identity",
    "Inspect shard ownership, process receipts and stale-worker rejection"
  ],
  "youWillBuild": "Build a persistent same-host evaluation coordinator that partitions recorded predictions, leases shards to real worker processes, fences stale completions and retains dataset-bound receipts.",
  "hours": 8,
  "languages": ["Go"],
  "status": "ready",
  "source": "core",
  "author": {
    "name": "AI Engineering from Scratch",
    "github": "rohitg00"
  },
  "skills": [
    "Partition stable case identities",
    "Fence each shard lease",
    "Accept idempotent completion receipts",
    "Run a bounded local worker pool"
  ],
  "prerequisites": [
    "Go 1.22 or later on Linux or macOS",
    "Python 3.10 or later for the grader",
    "Go structs, pointers, errors and JSON files",
    "Goroutines, channels and context cancellation"
  ],
  "inspiredBy": [],
  "demo": {
    "command": ["go", "run", ".", "demo"],
    "cwd": "solution"
  },
  "stages": [
    {
      "id": "01-partition-stable-case-identities",
      "title": "Partition stable case identities",
      "summary": "Assign each nonempty unique case ID to one of a positive number of shards using FNV-1a.",
      "hours": 2,
      "language": "go",
      "difficulty": "starter",
      "concepts": ["Stable ID", "Hash bytes", "Modulo count", "One partition"]
    },
    {
      "id": "02-fence-each-shard-lease",
      "title": "Fence each shard lease",
      "summary": "A coordinator owns a lease record.",
      "hours": 2,
      "language": "go",
      "difficulty": "core",
      "concepts": [
        "Unfinished shard",
        "Expiry check",
        "New owner",
        "Increment version"
      ]
    },
    {
      "id": "03-accept-idempotent-completion-receipts",
      "title": "Accept idempotent completion receipts",
      "summary": "A completion carries shard owner, lease version and a nonempty result.",
      "hours": 2,
      "language": "go",
      "difficulty": "core",
      "concepts": [
        "Owner and version",
        "Lease boundary",
        "Result identity",
        "Idempotent receipt"
      ]
    },
    {
      "id": "04-run-a-bounded-local-worker-pool",
      "title": "Run a bounded local worker pool",
      "summary": "Compose the bounded pool with persistent leases and actual worker processes; retain scored case coverage and reject stale receipts.",
      "hours": 2,
      "language": "go",
      "difficulty": "core",
      "concepts": [
        "Bounded goroutines",
        "Unique dispatch",
        "Cooperative cancellation",
        "Stable results"
      ],
      "timeout": 120
    }
  ],
  "demos": [
    {
      "gif": "media/run.gif",
      "poster": "media/run.png",
      "title": "Initialize and grade",
      "caption": "Recorded starter failure followed by all reference-solution stages passing. Reference passes do not earn learner certificates."
    },
    {
      "gif": "media/output.gif",
      "poster": "media/output.png",
      "title": "Inspect the output",
      "caption": "Actual output from the local deterministic demo command. See the README for fixture and live-adapter limits."
    }
  ]
}