# Claude Code v2.1.88 — Source Code Analysis

> Extracted from npm package `@anthropic-ai/claude-code` version **2.1.88**.
> The published package ships a single bundled `cli.js` (~12MB). The `src/` directory in this repo contains the **unbundled TypeScript source** extracted from the npm tarball.

---

## Copyright & Disclaimer

```
Copyright (c) Anthropic PBC. All rights reserved.

All source code in this repository is the intellectual property of Anthropic.
This repository is provided strictly for technical research and educational purposes.
Commercial use is strictly prohibited.

If you are the copyright owner and believe this repository infringes your rights,
please contact the repository owner for immediate removal.
```

---

## Stats

| Item | Count |
|------|-------|
| Source files (.ts/.tsx) | ~1,884 |
| Lines of code | ~512,664 |
| Largest single file | `query.ts` (~785KB) |
| Built-in tools | ~40+ |
| Slash commands | ~80+ |
| Dependencies (node_modules) | ~192 packages |
| Runtime | Bun (compiled to Node.js >= 18 bundle) |

---

## The Agent Pattern

```
                    THE CORE LOOP
                    =============

    User --> messages[] --> Claude API --> response
                                          |
                                stop_reason == "tool_use"?
                               /                          \
                             yes                           no
                              |                             |
                        execute tools                    return text
                        append tool_result
                        loop back -----------------> messages[]


    That is the minimal agent loop. Claude Code wraps this loop
    with a production-grade harness: permissions, streaming,
    concurrency, compaction, sub-agents, persistence, and MCP.
```

---

## Directory Reference

```
src/
├── main.tsx                 # REPL bootstrap, 4,683 lines
├── QueryEngine.ts           # SDK/headless query lifecycle engine
├── query.ts                 # Main agent loop (785KB, largest file)
├── Tool.ts                  # Tool interface + buildTool factory
├── Task.ts                  # Task types, IDs, state base
├── tools.ts                 # Tool registry, presets, filtering
├── commands.ts              # Slash command definitions
├── context.ts               # User input context
├── cost-tracker.ts          # API cost accumulation
├── setup.ts                 # First-run setup flow
│
├── bridge/                  # Claude Desktop / remote bridge
│   ├── bridgeMain.ts        #   Session lifecycle manager
│   ├── bridgeApi.ts         #   HTTP client
│   ├── bridgeConfig.ts      #   Connection config
│   ├── bridgeMessaging.ts   #   Message relay
│   ├── sessionRunner.ts     #   Process spawning
│   ├── jwtUtils.ts          #   JWT refresh
│   ├── workSecret.ts        #   Auth tokens
│   └── capacityWake.ts      #   Capacity-based wakeup
│
├── cli/                     # CLI infrastructure
│   ├── handlers/            #   Command handlers
│   └── transports/          #   I/O transports (stdio, structured)
│
├── commands/                # ~80 slash commands
│   ├── agents/              #   Agent management
│   ├── compact/             #   Context compaction
│   ├── config/              #   Settings management
│   ├── help/                #   Help display
│   ├── login/               #   Authentication
│   ├── mcp/                 #   MCP server management
│   ├── memory/              #   Memory system
│   ├── plan/                #   Plan mode
│   ├── resume/              #   Session resume
│   ├── review/              #   Code review
│   └── ...                  #   70+ more commands
│
├── components/              # React/Ink terminal UI
│   ├── design-system/       #   Reusable UI primitives
│   ├── messages/            #   Message rendering
│   ├── permissions/         #   Permission dialogs
│   ├── PromptInput/         #   Input field + suggestions
│   ├── LogoV2/              #   Branding + welcome screen
│   ├── Settings/            #   Settings panels
│   ├── Spinner.tsx          #   Loading indicators
│   └── ...                  #   40+ component groups
│
├── entrypoints/             # Application entry points
│   ├── cli.tsx              #   CLI main (version, help, daemon)
│   ├── sdk/                 #   Agent SDK (types, sessions)
│   └── mcp.ts               #   MCP server entry
│
├── hooks/                   # React hooks
│   ├── useCanUseTool.tsx    #   Permission checking
│   ├── useReplBridge.tsx    #   Bridge connection
│   ├── notifs/              #   Notification hooks
│   └── toolPermission/      #   Tool permission handlers
│
├── services/                # Business logic layer
│   ├── api/                 #   Claude API client
│   │   ├── claude.ts        #     Streaming API calls
│   │   ├── errors.ts        #     Error categorization
│   │   └── withRetry.ts     #     Retry logic
│   ├── analytics/           #   Telemetry + GrowthBook
│   ├── compact/             #   Context compression
│   ├── mcp/                 #   MCP connection management
│   ├── tools/               #   Tool execution engine
│   │   ├── StreamingToolExecutor.ts  # Parallel tool runner
│   │   └── toolOrchestration.ts      # Batch orchestration
│   ├── plugins/             #   Plugin loader
│   └── settingsSync/        #   Cross-device settings
│
├── state/                   # Application state
│   ├── AppStateStore.ts     #   Store definition
│   └── AppState.tsx         #   React provider + hooks
│
├── tasks/                   # Task implementations
│   ├── LocalShellTask/      #   Bash command execution
│   ├── LocalAgentTask/      #   Sub-agent execution
│   ├── RemoteAgentTask/     #   Remote agent via bridge
│   ├── InProcessTeammateTask/ # In-process teammate
│   └── DreamTask/           #   Background thinking
│
├── tools/                   # 40+ tool implementations
│   ├── AgentTool/           #   Sub-agent spawning + fork
│   ├── BashTool/            #   Shell command execution
│   ├── FileReadTool/        #   File reading (PDF, image, etc)
│   ├── FileEditTool/        #   String-replace editing
│   ├── FileWriteTool/       #   Full file creation
│   ├── GlobTool/            #   File pattern search
│   ├── GrepTool/            #   Content search (ripgrep)
│   ├── WebFetchTool/        #   HTTP fetching
│   ├── WebSearchTool/       #   Web search
│   ├── MCPTool/             #   MCP tool wrapper
│   ├── SkillTool/           #   Skill invocation
│   ├── AskUserQuestionTool/ #   User interaction
│   └── ...                  #   30+ more tools
│
├── types/                   # Type definitions
│   ├── message.ts           #   Message discriminated unions
│   ├── permissions.ts       #   Permission types
│   ├── tools.ts             #   Tool progress types
│   └── ids.ts               #   Branded ID types
│
├── utils/                   # Utilities (largest directory)
│   ├── permissions/         #   Permission rule engine
│   ├── messages/            #   Message formatting
│   ├── model/               #   Model selection logic
│   ├── settings/            #   Settings management
│   ├── sandbox/             #   Sandbox runtime adapter
│   ├── hooks/               #   Hook execution
│   ├── memory/              #   Memory system utils
│   ├── git/                 #   Git operations
│   ├── github/              #   GitHub API
│   ├── bash/                #   Bash execution helpers
│   ├── swarm/               #   Multi-agent swarm
│   ├── telemetry/           #   Telemetry reporting
│   └── ...                  #   30+ more util groups
│
└── vendor/                  # Native module source stubs
    ├── audio-capture-src/   #   Audio input
    ├── image-processor-src/ #   Image processing
    ├── modifiers-napi-src/  #   Native modifiers
    └── url-handler-src/     #   URL handling
```

---

## Architecture Overview

```
┌─────────────────────────────────────────────────────────────────────┐
│                         ENTRY LAYER                                 │
│  cli.tsx ──> main.tsx ──> REPL.tsx (interactive)                   │
│                     └──> QueryEngine.ts (headless/SDK)              │
└──────────────────────────────┬──────────────────────────────────────┘
                               │
                               ▼
┌─────────────────────────────────────────────────────────────────────┐
│                       QUERY ENGINE                                  │
│  submitMessage(prompt) ──> AsyncGenerator<SDKMessage>               │
│    │                                                                │
│    ├── fetchSystemPromptParts()    ──> assemble system prompt       │
│    ├── processUserInput()          ──> handle /commands             │
│    ├── query()                     ──> main agent loop              │
│    │     ├── StreamingToolExecutor ──> parallel tool execution       │
│    │     ├── autoCompact()         ──> context compression          │
│    │     └── runTools()            ──> tool orchestration           │
│    └── yield SDKMessage            ──> stream to consumer           │
└──────────────────────────────┬──────────────────────────────────────┘
                               │
              ┌────────────────┼────────────────┐
              ▼                ▼                 ▼
┌──────────────────┐ ┌─────────────────┐ ┌──────────────────┐
│   TOOL SYSTEM    │ │  SERVICE LAYER  │ │   STATE LAYER    │
│                  │ │                 │ │                  │
│ Tool Interface   │ │ api/claude.ts   │ │ AppState Store   │
│  ├─ call()       │ │  API client     │ │  ├─ permissions  │
│  ├─ validate()   │ │ compact/        │ │  ├─ fileHistory  │
│  ├─ checkPerms() │ │  auto-compact   │ │  ├─ agents       │
│  ├─ render()     │ │ mcp/            │ │  └─ fastMode     │
│  └─ prompt()     │ │  MCP protocol   │ │                  │
│                  │ │ analytics/      │ │ React Context    │
│ 40+ Built-in:    │ │  telemetry      │ │  ├─ useAppState  │
│  ├─ BashTool     │ │ tools/          │ │  └─ useSetState  │
│  ├─ FileRead     │ │  executor       │ │                  │
│  ├─ FileEdit     │ │ plugins/        │ └──────────────────┘
│  ├─ Glob/Grep    │ │  loader         │
│  ├─ AgentTool    │ │ settingsSync/   │
│  ├─ WebFetch     │ │  cross-device   │
│  └─ MCPTool      │ │ oauth/          │
│                  │ │  auth flow      │
└──────────────────┘ └─────────────────┘
              │                │
              ▼                ▼
┌──────────────────┐ ┌─────────────────┐
│   TASK SYSTEM    │ │   BRIDGE LAYER  │
│                  │ │                 │
│ Task Types:      │ │ bridgeMain.ts   │
│  ├─ local_bash   │ │  session mgmt   │
│  ├─ local_agent  │ │ bridgeApi.ts    │
│  ├─ remote_agent │ │  HTTP client    │
│  ├─ in_process   │ │ workSecret.ts   │
│  ├─ dream        │ │  auth tokens    │
│  └─ workflow     │ │ sessionRunner   │
│                  │ │  process spawn  │
│ ID: prefix+8chr  │ └─────────────────┘
│  b=bash a=agent  │
│  r=remote t=team │
└──────────────────┘
```

---

## Data Flow: A Single Query Lifecycle

```
 USER INPUT (prompt / slash command)
     │
     ▼
 processUserInput()                ← parse /commands, build UserMessage
     │
     ▼
 fetchSystemPromptParts()          ← tools → prompt sections, CLAUDE.md memory
     │
     ▼
 recordTranscript()                ← persist user message to disk (JSONL)
     │
     ▼
 ┌─→ normalizeMessagesForAPI()     ← strip UI-only fields, compact if needed
 │   │
 │   ▼
 │   Claude API (streaming)        ← POST /v1/messages with tools + system prompt
 │   │
 │   ▼
 │   stream events                 ← message_start → content_block_delta → message_stop
 │   │
 │   ├─ text block ──────────────→ yield to consumer (SDK / REPL)
 │   │
 │   └─ tool_use block?
 │       │
 │       ▼
 │   StreamingToolExecutor         ← partition: concurrent-safe vs serial
 │       │
 │       ▼
 │   canUseTool()                  ← permission check (hooks + rules + UI prompt)
 │       │
 │       ├─ DENY ────────────────→ append tool_result(error), continue loop
 │       │
 │       └─ ALLOW
 │           │
 │           ▼
 │       tool.call()               ← execute the tool (Bash, Read, Edit, etc.)
 │           │
 │           ▼
 │       append tool_result        ← push to messages[], recordTranscript()
 │           │
 └─────────┘                      ← loop back to API call
     │
     ▼ (stop_reason != "tool_use")
 yield result message              ← final text, usage, cost, session_id
```

---

## Tool System Architecture

```
                    TOOL INTERFACE
                    ==============

    buildTool(definition) ──> Tool<Input, Output, Progress>

    Every tool implements:
    ┌────────────────────────────────────────────────────────┐
    │  LIFECYCLE                                             │
    │  ├── validateInput()      → reject bad args early     │
    │  ├── checkPermissions()   → tool-specific authz       │
    │  └── call()               → execute and return result │
    │                                                        │
    │  CAPABILITIES                                          │
    │  ├── isEnabled()          → feature gate check        │
    │  ├── isConcurrencySafe()  → can run in parallel?      │
    │  ├── isReadOnly()         → no side effects?          │
    │  ├── isDestructive()      → irreversible ops?         │
    │  └── interruptBehavior()  → cancel or block on user?  │
    │                                                        │
    │  RENDERING (React/Ink)                                 │
    │  ├── renderToolUseMessage()     → input display        │
    │  ├── renderToolResultMessage()  → output display       │
    │  ├── renderToolUseProgressMessage() → spinner/status   │
    │  └── renderGroupedToolUse()     → parallel tool groups │
    │                                                        │
    │  AI FACING                                             │
    │  ├── prompt()             → tool description for LLM  │
    │  ├── description()        → dynamic description       │
    │  └── mapToolResultToAPI() → format for API response   │
    └────────────────────────────────────────────────────────┘
```

### Complete Tool Inventory

```
    FILE OPERATIONS          SEARCH & DISCOVERY        EXECUTION
    ═════════════════        ══════════════════════     ══════════
    FileReadTool             GlobTool                  BashTool
    FileEditTool             GrepTool                  PowerShellTool
    FileWriteTool            ToolSearchTool
    NotebookEditTool                                   INTERACTION
                                                       ═══════════
    WEB & NETWORK           AGENT / TASK              AskUserQuestionTool
    ════════════════        ══════════════════        BriefTool
    WebFetchTool             AgentTool
    WebSearchTool            SendMessageTool           PLANNING & WORKFLOW
                             TeamCreateTool            ════════════════════
    MCP PROTOCOL             TeamDeleteTool            EnterPlanModeTool
    ══════════════           TaskCreateTool            ExitPlanModeTool
    MCPTool                  TaskGetTool               EnterWorktreeTool
    ListMcpResourcesTool     TaskUpdateTool            ExitWorktreeTool
    ReadMcpResourceTool      TaskListTool              TodoWriteTool
                             TaskStopTool
                             TaskOutputTool            SYSTEM
                                                       ════════
                             SKILLS & EXTENSIONS       ConfigTool
                             ═════════════════════     SkillTool
                             SkillTool                 ScheduleCronTool
                             LSPTool                   SleepTool
                                                       TungstenTool
```

---

## Permission System

```
    TOOL CALL REQUEST
          │
          ▼
    ┌─ validateInput() ──────────────────────────────────┐
    │  reject invalid inputs before any permission check │
    └────────────────────┬───────────────────────────────┘
                         │
                         ▼
    ┌─ PreToolUse Hooks ─────────────────────────────────┐
    │  user-defined shell commands (settings.json hooks) │
    │  can: approve, deny, or modify input               │
    └────────────────────┬───────────────────────────────┘
                         │
                         ▼
    ┌─ Permission Rules ─────────────────────────────────┐
    │  alwaysAllowRules:  match tool name/pattern → auto │
    │  alwaysDenyRules:   match tool name/pattern → deny │
    │  alwaysAskRules:    match tool name/pattern → ask  │
    │  Sources: settings, CLI args, session decisions    │
    └────────────────────┬───────────────────────────────┘
                         │
                    no rule match?
                         │
                         ▼
    ┌─ Interactive Prompt ───────────────────────────────┐
    │  User sees tool name + input                       │
    │  Options: Allow Once / Allow Always / Deny         │
    └────────────────────┬───────────────────────────────┘
                         │
                         ▼
    ┌─ checkPermissions() ───────────────────────────────┐
    │  Tool-specific logic (e.g. path sandboxing)        │
    └────────────────────┬───────────────────────────────┘
                         │
                    APPROVED → tool.call()
```

---

## Sub-Agent & Multi-Agent Architecture

```
                        MAIN AGENT
                        ==========
                            │
            ┌───────────────┼───────────────┐
            ▼               ▼               ▼
     ┌──────────────┐ ┌──────────┐ ┌──────────────┐
     │  FORK AGENT  │ │ REMOTE   │ │ IN-PROCESS   │
     │              │ │ AGENT    │ │ TEAMMATE     │
     │ Fork process │ │ Bridge   │ │ Same process │
     │ Shared cache │ │ session  │ │ Async context│
     │ Fresh msgs[] │ │ Isolated │ │ Shared state │
     └──────────────┘ └──────────┘ └──────────────┘

    SPAWN MODES:
    ├─ default    → in-process, shared conversation
    ├─ fork       → child process, fresh messages[], shared file cache
    ├─ worktree   → isolated git worktree + fork
    └─ remote     → bridge to Claude Code Remote / container

    COMMUNICATION:
    ├─ SendMessageTool     → agent-to-agent messages
    ├─ TaskCreate/Update   → shared task board
    └─ TeamCreate/Delete   → team lifecycle management

    SWARM MODE (feature-gated):
    ┌─────────────────────────────────────────────┐
    │  Lead Agent                                 │
    │    ├── Teammate A ──> claims Task 1         │
    │    ├── Teammate B ──> claims Task 2         │
    │    └── Teammate C ──> claims Task 3         │
    │                                             │
    │  Shared: task board, message inbox          │
    │  Isolated: messages[], file cache, cwd      │
    └─────────────────────────────────────────────┘
```

---

## Context Management (Compact System)

```
    CONTEXT WINDOW BUDGET
    ═════════════════════

    ┌─────────────────────────────────────────────────────┐
    │  System Prompt (tools, permissions, CLAUDE.md)      │
    │  ══════════════════════════════════════════════      │
    │                                                     │
    │  Conversation History                               │
    │  ┌─────────────────────────────────────────────┐    │
    │  │ [compacted summary of older messages]        │    │
    │  │ ═══════════════════════════════════════════  │    │
    │  │ [compact_boundary marker]                    │    │
    │  │ ─────────────────────────────────────────── │    │
    │  │ [recent messages — full fidelity]            │    │
    │  │ user → assistant → tool_use → tool_result   │    │
    │  └─────────────────────────────────────────────┘    │
    │                                                     │
    │  Current Turn (user + assistant response)            │
    └─────────────────────────────────────────────────────┘

    THREE COMPRESSION STRATEGIES:
    ├─ autoCompact     → triggers when token count exceeds threshold
    │                     summarizes old messages via a compact API call
    ├─ snipCompact     → removes zombie messages and stale markers
    │                     (HISTORY_SNIP feature flag)
    └─ contextCollapse → restructures context for efficiency
                         (CONTEXT_COLLAPSE feature flag)

    COMPACTION FLOW:
    messages[] ──> getMessagesAfterCompactBoundary()
                        │
                        ▼
                  older messages ──> Claude API (summarize) ──> compact summary
                        │
                        ▼
                  [summary] + [compact_boundary] + [recent messages]
```

---

## MCP (Model Context Protocol) Integration

```
    ┌─────────────────────────────────────────────────────────┐
    │                  MCP ARCHITECTURE                        │
    │                                                         │
    │  MCPConnectionManager.tsx                               │
    │    ├── Server Discovery (config from settings.json)     │
    │    │     ├── stdio  → spawn child process               │
    │    │     ├── sse    → HTTP EventSource                  │
    │    │     ├── http   → Streamable HTTP                   │
    │    │     ├── ws     → WebSocket                         │
    │    │     └── sdk    → in-process transport              │
    │    │                                                    │
    │    ├── Client Lifecycle                                  │
    │    │     ├── connect → initialize → list tools          │
    │    │     ├── tool calls via MCPTool wrapper              │
    │    │     └── disconnect / reconnect with backoff        │
    │    │                                                    │
    │    ├── Authentication                                   │
    │    │     ├── OAuth 2.0 flow (McpOAuthConfig)            │
    │    │     ├── Cross-App Access (XAA / SEP-990)           │
    │    │     └── API key via headers                        │
    │    │                                                    │
    │    └── Tool Registration                                │
    │          ├── mcp__<server>__<tool> naming convention     │
    │          ├── Dynamic schema from MCP server              │
    │          ├── Permission passthrough to Claude Code       │
    │          └── Resource listing (ListMcpResourcesTool)     │
    │                                                         │
    └─────────────────────────────────────────────────────────┘
```

---

## Bridge Layer (Claude Desktop / Remote)

```
    Claude Desktop / Web / Cowork          Claude Code CLI
    ══════════════════════════            ═════════════════

    ┌───────────────────┐                 ┌──────────────────┐
    │  Bridge Client    │  ←─ HTTP ──→   │  bridgeMain.ts   │
    │  (Desktop App)    │                 │                  │
    └───────────────────┘                 │  Session Manager │
                                          │  ├── spawn CLI   │
    PROTOCOL:                             │  ├── poll status  │
    ├─ JWT authentication                 │  ├── relay msgs   │
    ├─ Work secret exchange               │  └── capacityWake │
    ├─ Session lifecycle                  │                  │
    │  ├── create                         │  Backoff:        │
    │  ├── run                            │  ├─ conn: 2s→2m  │
    │  └─ stop                            │  └─ gen: 500ms→30s│
    └─ Token refresh scheduler            └──────────────────┘
```

---

## Session Persistence

```
    SESSION STORAGE
    ══════════════

    ~/.claude/projects/<hash>/sessions/
    └── <session-id>.jsonl           ← append-only log
        ├── {"type":"user",...}
        ├── {"type":"assistant",...}
        ├── {"type":"progress",...}
        └── {"type":"system","subtype":"compact_boundary",...}

    RESUME FLOW:
    getLastSessionLog() ──> parse JSONL ──> rebuild messages[]
         │
         ├── --continue     → last session in cwd
         ├── --resume <id>  → specific session
         └── --fork-session → new ID, copy history

    PERSISTENCE STRATEGY:
    ├─ User messages  → await write (blocking, for crash recovery)
    ├─ Assistant msgs → fire-and-forget (order-preserving queue)
    ├─ Progress       → inline write (dedup on next query)
    └─ Flush          → on result yield / cowork eager flush
```

---

## Feature Flag System

```
    DEAD CODE ELIMINATION (Bun compile-time)
    ══════════════════════════════════════════

    feature('FLAG_NAME')  ──→  true  → included in bundle
                           ──→  false → stripped from bundle

    FLAGS (observed in source):
    ├─ COORDINATOR_MODE      → multi-agent coordinator
    ├─ HISTORY_SNIP          → aggressive history trimming
    ├─ CONTEXT_COLLAPSE      → context restructuring
    ├─ DAEMON                → background daemon workers
    ├─ AGENT_TRIGGERS        → cron/remote triggers
    ├─ AGENT_TRIGGERS_REMOTE → remote trigger support
    ├─ MONITOR_TOOL          → MCP monitoring tool
    ├─ WEB_BROWSER_TOOL      → browser automation
    ├─ VOICE_MODE            → voice input/output
    ├─ TEMPLATES             → job classifier
    ├─ EXPERIMENTAL_SKILL_SEARCH → skill discovery
    ├─ KAIROS                → push notifications, file sends
    ├─ PROACTIVE             → sleep tool, proactive behavior
    ├─ OVERFLOW_TEST_TOOL    → testing tool
    ├─ TERMINAL_PANEL        → terminal capture
    ├─ WORKFLOW_SCRIPTS      → workflow tool
    ├─ CHICAGO_MCP           → computer use MCP
    ├─ DUMP_SYSTEM_PROMPT    → prompt extraction (ant-only)
    ├─ UDS_INBOX             → peer discovery
    ├─ ABLATION_BASELINE     → experiment ablation
    └─ UPGRADE_NOTICE        → upgrade notifications

    RUNTIME GATES:
    ├─ process.env.USER_TYPE === 'ant'  → Anthropic-internal features
    └─ GrowthBook feature flags         → A/B experiments at runtime
```

---

## State Management

```
    ┌──────────────────────────────────────────────────────────┐
    │                  AppState Store                           │
    │                                                          │
    │  AppState {                                              │
    │    toolPermissionContext: {                              │
    │      mode: PermissionMode,           ← default/plan/etc │
    │      additionalWorkingDirectories,                        │
    │      alwaysAllowRules,               ← auto-approve      │
    │      alwaysDenyRules,                ← auto-reject       │
    │      alwaysAskRules,                 ← always prompt     │
    │      isBypassPermissionsModeAvailable                    │
    │    },                                                    │
    │    fileHistory: FileHistoryState,    ← undo snapshots    │
    │    attribution: AttributionState,    ← commit tracking   │
    │    verbose: boolean,                                     │
    │    mainLoopModel: string,           ← active model       │
    │    fastMode: FastModeState,                              │
    │    speculation: SpeculationState                          │
    │  }                                                       │
    │                                                          │
    │  React Integration:                                      │
    │  ├── AppStateProvider   → creates store via createContext │
    │  ├── useAppState(sel)   → selector-based subscriptions   │
    │  └── useSetAppState()   → immer-style updater function   │
    └──────────────────────────────────────────────────────────┘
```

---

## The 12 Progressive Harness Mechanisms

This source code demonstrates 12 layered mechanisms that a production AI agent harness needs beyond the basic loop. Each builds on the previous:

```
    s01  THE LOOP             "One loop & Bash is all you need"
         query.ts: the while-true loop that calls Claude API,
         checks stop_reason, executes tools, appends results.

    s02  TOOL DISPATCH        "Adding a tool = adding one handler"
         Tool.ts + tools.ts: every tool registers into the dispatch
         map. The loop stays identical. buildTool() factory provides
         safe defaults.

    s03  PLANNING             "An agent without a plan drifts"
         EnterPlanModeTool/ExitPlanModeTool + TodoWriteTool:
         list steps first, then execute. Doubles completion rate.

    s04  SUB-AGENTS           "Break big tasks; clean context per subtask"
         AgentTool + forkSubagent.ts: each child gets fresh messages[],
         keeping the main conversation clean.

    s05  KNOWLEDGE ON DEMAND  "Load knowledge when you need it"
         SkillTool + memdir/: inject via tool_result, not system prompt.
         CLAUDE.md files loaded lazily per directory.

    s06  CONTEXT COMPRESSION  "Context fills up; make room"
         services/compact/: three-layer strategy:
         autoCompact (summarize) + snipCompact (trim) + contextCollapse

    s07  PERSISTENT TASKS     "Big goals → small tasks → disk"
         TaskCreate/Update/Get/List: file-based task graph with
         status tracking, dependencies, and persistence.

    s08  BACKGROUND TASKS     "Slow ops in background; agent keeps thinking"
         DreamTask + LocalShellTask: daemon threads run commands,
         inject notifications on completion.

    s09  AGENT TEAMS          "Too big for one → delegate to teammates"
         TeamCreate/Delete + InProcessTeammateTask: persistent
         teammates with async mailboxes.

    s10  TEAM PROTOCOLS       "Shared communication rules"
         SendMessageTool: one request-response pattern drives
         all negotiation between agents.

    s11  AUTONOMOUS AGENTS    "Teammates scan and claim tasks themselves"
         coordinator/coordinatorMode.ts: idle cycle + auto-claim,
         no need for lead to assign each task.

    s12  WORKTREE ISOLATION   "Each works in its own directory"
         EnterWorktreeTool/ExitWorktreeTool: tasks manage goals,
         worktrees manage directories, bound by ID.
```

---

## Key Design Patterns

| Pattern | Where | Purpose |
|---------|-------|---------|
| **AsyncGenerator streaming** | `QueryEngine`, `query()` | Full-chain streaming from API to consumer |
| **Builder + Factory** | `buildTool()` | Safe defaults for tool definitions |
| **Branded Types** | `SystemPrompt`, `asSystemPrompt()` | Prevent string/array confusion |
| **Feature Flags + DCE** | `feature()` from `bun:bundle` | Compile-time dead code elimination |
| **Discriminated Unions** | `Message` types | Type-safe message handling |
| **Observer + State Machine** | `StreamingToolExecutor` | Tool execution lifecycle tracking |
| **Snapshot State** | `FileHistoryState` | Undo/redo for file operations |
| **Ring Buffer** | Error log | Bounded memory for long sessions |
| **Fire-and-Forget Write** | `recordTranscript()` | Non-blocking persistence with ordering |
| **Lazy Schema** | `lazySchema()` | Defer Zod schema evaluation for performance |
| **Context Isolation** | `AsyncLocalStorage` | Per-agent context in shared process |

---

## Build Notes

This source is **not directly compilable** from this repo alone:

- Missing `tsconfig.json`, build scripts, and Bun bundler config
- `feature()` calls are Bun compile-time intrinsics — resolved during bundling
- `MACRO.VERSION` is injected at build time
- `process.env.USER_TYPE === 'ant'` sections are Anthropic-internal
- The compiled `cli.js` is a self-contained 12MB bundle requiring only Node.js >= 18
- Source maps (`cli.js.map`, 60MB) map back to these source files for debugging

---

## License

All source code in this repository is copyright **Anthropic PBC**. This repository is for technical research and education only. See the original npm package for full license terms.
