{
  "id": "desktop-control",
  "title": "Desktop Control Backend",
  "level": 4,
  "levelName": "Systems",
  "tagline": "An auditable coordinate-and-frame action runner with reproducible before/after pixel artifacts.",
  "summary": "An auditable coordinate-and-frame action runner with reproducible before/after pixel artifacts. The Backend trait is the reusable boundary. TSV uses capture, click<TAB>x<TAB>y<TAB>generation and type<TAB>text; the runner refuses unknown actions and caps32 calls.",
  "hours": 8,
  "languages": ["Rust"],
  "status": "ready",
  "source": "core",
  "author": {
    "name": "AI Engineering from Scratch",
    "github": "rohitg00"
  },
  "skills": [
    "Validate frames and coordinate spaces",
    "Render and manipulate a fixture scene",
    "Reject stale observations and exhausted budgets",
    "Build an opt-in native boundary"
  ],
  "prerequisites": [
    "Rust 2021 toolchain",
    "structs, traits, generics, Result, mutable borrowing and byte vectors. Python 3 runs the grader and demo wrapper."
  ],
  "youWillBuild": "An auditable coordinate-and-frame action runner with reproducible before/after pixel artifacts.",
  "usefulFor": [
    "The Backend trait is the reusable boundary. TSV uses capture, click<TAB>x<TAB>y<TAB>generation and type<TAB>text; the runner refuses unknown actions and caps32 calls."
  ],
  "demo": {
    "command": ["python3", "demo.py"],
    "cwd": "solution"
  },
  "stages": [
    {
      "id": "01-frame-contract",
      "title": "Validate frames and coordinate spaces",
      "summary": "A screenshot has physical pixel dimensions while native desktop clicks may use logical coordinates.",
      "hours": 2,
      "language": "rust",
      "languageWhy": "Rust makes state ownership and fallible system calls explicit while keeping the implementation in the standard library.",
      "requires": ["rustc"],
      "difficulty": "starter",
      "concepts": ["Frame.validate", "Frame.logical_point"],
      "figure": "pj-desktop-control-1",
      "timeout": 90
    },
    {
      "id": "02-backend-trait",
      "title": "Render and manipulate a fixture scene",
      "summary": "Define capture, click and type_text behind one Backend trait.",
      "hours": 2,
      "language": "rust",
      "languageWhy": "Rust makes state ownership and fallible system calls explicit while keeping the implementation in the standard library.",
      "requires": ["rustc"],
      "difficulty": "core",
      "concepts": ["Backend", "FixtureBackend"],
      "figure": "pj-desktop-control-2",
      "timeout": 90
    },
    {
      "id": "03-controller",
      "title": "Reject stale observations and exhausted budgets",
      "summary": "Place a Controller around the backend.",
      "hours": 2,
      "language": "rust",
      "languageWhy": "Rust makes state ownership and fallible system calls explicit while keeping the implementation in the standard library.",
      "requires": ["rustc"],
      "difficulty": "core",
      "concepts": [
        "Controller.capture",
        "Controller.click",
        "Controller.type_text"
      ],
      "figure": "pj-desktop-control-3",
      "timeout": 90
    },
    {
      "id": "04-native-adapter",
      "title": "Build an opt-in native boundary",
      "summary": "Construct macOS screencapture and AppleScript argument arrays without a shell.",
      "hours": 2,
      "language": "rust",
      "languageWhy": "Rust makes state ownership and fallible system calls explicit while keeping the implementation in the standard library.",
      "requires": ["rustc"],
      "difficulty": "core",
      "concepts": ["click_argv", "text_argv", "png_dimensions", "MacBackend"],
      "figure": "pj-desktop-control-4",
      "timeout": 90
    }
  ],
  "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."
    }
  ]
}