{
  "id": "tool-call-firewall",
  "title": "Tool Call Firewall",
  "level": 4,
  "levelName": "Systems",
  "tagline": "Authorize structured tool requests before they cross a side-effect boundary.",
  "summary": "Build a deny-by-default policy evaluator with bounded arguments, role permissions, single-use approvals and a structured audit log. The artifact is a library gate; applications must place it before every real tool execution.",
  "usefulFor": [
    "An approval receipt proving exactly which operation was authorized and executed.",
    "The native CLI requires a trusted role from the invoking application."
  ],
  "youWillBuild": "An approval receipt proving exactly which operation was authorized and executed.",
  "hours": 8,
  "languages": [
    "Rust"
  ],
  "status": "ready",
  "source": "core",
  "author": {
    "name": "AI Engineering from Scratch",
    "github": "rohitg00"
  },
  "skills": [
    "Validate an unambiguous call envelope",
    "Evaluate role and path policy",
    "Consume a request-bound approval once",
    "Record bounded audit evidence"
  ],
  "prerequisites": [
    {
      "title": "Tool schema design",
      "path": "phases/13-tools-and-protocols/05-tool-schema-design"
    },
    {
      "title": "Security and secrets audit",
      "path": "phases/17-infrastructure-and-production/25-security-secrets-audit"
    }
  ],
  "inspiredBy": [],
  "demo": {
    "command": [
      "python3",
      "demo.py"
    ],
    "cwd": "solution"
  },
  "stages": [
    {
      "id": "01-validate-an-unambiguous-call-envelope",
      "title": "Validate an unambiguous call envelope",
      "summary": "Parse a bounded four-field envelope using a pipe delimiter for this local exercise.",
      "hours": 2,
      "language": "rust",
      "difficulty": "starter",
      "concepts": [
        "Byte budget",
        "Envelope fields",
        "Control gate",
        "Call identity"
      ]
    },
    {
      "id": "02-evaluate-role-and-path-policy",
      "title": "Evaluate role and path policy",
      "summary": "Only reader and editor roles exist.",
      "hours": 2,
      "language": "rust",
      "difficulty": "core",
      "concepts": [
        "Known role",
        "Path components",
        "Tool permission",
        "Decision"
      ]
    },
    {
      "id": "03-consume-a-request-bound-approval-once",
      "title": "Consume a request-bound approval once",
      "summary": "An approval is bound to the complete call identity supplied by a trusted application and is consumed only for an approval-required decision.",
      "hours": 2,
      "language": "rust",
      "difficulty": "core",
      "concepts": [
        "Decision gate",
        "Match identity",
        "Check unused",
        "Consume once"
      ]
    },
    {
      "id": "04-record-bounded-audit-evidence",
      "title": "Record bounded audit evidence",
      "summary": "Format a stable tab-separated audit row after the policy decision.",
      "hours": 2,
      "language": "rust",
      "difficulty": "core",
      "concepts": [
        "Unique call",
        "Capacity check",
        "Omit arguments",
        "Record decision"
      ]
    }
  ],
  "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."
    }
  ]
}