{
  "id": "02-architecture",
  "title": "Architecture without the mystery",
  "icon": "🏗",
  "level": "beginner",
  "lessons": [
    {
      "id": "2.1",
      "title": "Terminal, modules, commands",
      "objective": "See what is loaded, why a command can be listed but broken, and what the system is doing.",
      "minutes": 9,
      "commands": [
        "modules",
        "doctor",
        "status"
      ],
      "blocks": [
        {
          "type": "text",
          "text": "`terminal.js` parses input and dispatches a command to the module that registered it. Each module owns a `commands` map and contributes help strings."
        },
        {
          "type": "cmd",
          "text": "modules"
        },
        {
          "type": "text",
          "text": "The module manager lists every loaded module and its command count."
        },
        {
          "type": "cmd",
          "text": "status"
        },
        {
          "type": "text",
          "text": "`status` shows files, modules and network state in one place."
        },
        {
          "type": "cmd",
          "text": "doctor"
        },
        {
          "type": "tip",
          "text": "A command that exists in `help` but fails at runtime usually has an unmet module requirement that `doctor` reports."
        }
      ],
      "exercise": {
        "instruction": "Run `doctor` and see how it ranks module problems.",
        "accept": [
          "doctor",
          "modules",
          "module-info *"
        ],
        "check": {
          "type": "command"
        },
        "hint": "Type: doctor"
      },
      "quiz": {
        "q": "Who executes a command after you press Enter?",
        "options": [
          "nginx",
          "the module that registered it",
          "the browser cache"
        ],
        "answer": 1
      },
      "sources": [
        "modules/core/terminal.js",
        "modules/core/module-manager.js",
        "modules/core/module-system.js"
      ]
    },
    {
      "id": "2.2",
      "title": "VFS and the three loading tiers",
      "objective": "Understand where files live and why a module edit sometimes needs a rebuild and sometimes does not.",
      "minutes": 10,
      "commands": [
        "pwd",
        "cd",
        "tree",
        "health-check",
        "mem"
      ],
      "blocks": [
        {
          "type": "text",
          "text": "Files live in `virtual-fs.js` (in-memory + localStorage persistence). Directories are nodes; `readFile()` returns `null` for a missing path."
        },
        {
          "type": "text",
          "text": "Modules ship in three tiers:"
        },
        {
          "type": "table",
          "text": "core-bundle.js — core modules (requires rebuild) | critical-ext-bundle.js — editor, shell, alias, finder, filemgr, diff, busybox (requires rebuild) | individually loaded ext modules — cache-busted by LATEST_VER (no rebuild)"
        },
        {
          "type": "cmd",
          "text": "status"
        },
        {
          "type": "warn",
          "text": "Individually loaded modules are cached with `?v=<webx11_cache_ver>`. Without bumping `LATEST_VER`, users keep the old file."
        }
      ],
      "exercise": {
        "instruction": "Run `health-check` and find the VFS size line.",
        "accept": [
          "health-check",
          "mem"
        ],
        "check": {
          "type": "command"
        },
        "hint": "Type: health-check"
      },
      "quiz": {
        "q": "Which tier needs `rebuild-bundles.py` after an edit?",
        "options": [
          "core-bundle.js",
          "webdav.js",
          "course.js"
        ],
        "answer": 0
      },
      "sources": [
        "modules/core/virtual-fs.js",
        "modules/core/module-loader.js",
        "scripts/rebuild-bundles.py"
      ]
    }
  ]
}