oh-my-pi/packages/coding-agent/DEVELOPMENT.md

coding-agent Development Guide

This document describes the architecture and development workflow for the coding-agent package.

Architecture Overview

The coding-agent is structured into distinct layers:

┌─────────────────────────────────────────────────────────────┐
│                         CLI Layer                           │
│  cli.ts → main.ts → cli/args.ts, cli/file-processor.ts     │
└─────────────────────────────────────────────────────────────┘
                              │
                              ▼
┌─────────────────────────────────────────────────────────────┐
│                       Mode Layer                            │
│  modes/interactive/   modes/print-mode.ts   modes/rpc/     │
└─────────────────────────────────────────────────────────────┘
                              │
                              ▼
┌─────────────────────────────────────────────────────────────┐
│                       Core Layer                            │
│  core/agent-session.ts, core/sdk.ts (SDK wrapper)          │
│  core/session-manager.ts, core/model-resolver.ts, etc.     │
└─────────────────────────────────────────────────────────────┘
                              │
                              ▼
┌─────────────────────────────────────────────────────────────┐
│                   External Dependencies                     │
│  @oh-my-pi/pi-agent-core (Agent core)                      │
│  @oh-my-pi/pi-ai (models, providers)                   │
│  @oh-my-pi/pi-tui (TUI components)                         │
└─────────────────────────────────────────────────────────────┘

Directory Structure

src/
├── cli.ts                    # CLI entry point (shebang, calls main)
├── main.ts                   # Main orchestration, argument handling, mode routing
├── index.ts                  # Public API exports (SDK)
├── config.ts                 # APP_NAME, VERSION, paths (getAgentDir, etc.)
├── migrations.ts             # Session/config migration logic

├── cli/                      # CLI-specific utilities
│   ├── args.ts               # parseArgs(), printHelp(), Args interface
│   ├── file-processor.ts     # processFileArguments() for @file args
│   ├── list-models.ts        # --list-models implementation
│   ├── plugin-cli.ts         # Plugin management CLI
│   ├── session-picker.ts     # selectSession() TUI for --resume
│   └── update-cli.ts         # Self-update CLI

├── capability/               # Capability system (extension types)
│   ├── index.ts              # Main capability registry and discovery
│   ├── context-file.ts       # Context file capability
│   ├── extension.ts          # Extension capability
│   ├── hook.ts               # Hook capability
│   ├── instruction.ts        # Instruction capability
│   ├── mcp.ts                # MCP capability
│   ├── prompt.ts             # Prompt capability
│   ├── rule.ts               # Rulebook rule capability
│   ├── skill.ts              # Skill capability
│   ├── slash-command.ts      # Slash command capability
│   ├── system-prompt.ts      # System prompt capability
│   └── tool.ts               # Tool capability

├── discovery/                # Extension discovery from multiple sources
│   ├── index.ts              # Main discovery orchestration
│   ├── builtin.ts            # Built-in extensions
│   ├── claude.ts             # Claude.md discovery
│   ├── cline.ts              # Cline .mcp.json discovery
│   ├── codex.ts              # .codex discovery
│   ├── cursor.ts             # Cursor .cursorrules discovery
│   ├── gemini.ts             # Gemini .config discovery
│   ├── github.ts             # GitHub extension discovery
│   ├── mcp-json.ts           # MCP JSON discovery
│   ├── vscode.ts             # VSCode extension discovery
│   ├── windsurf.ts           # Windsurf discovery
│   └── helpers.ts            # Discovery helper functions

├── prompts/                  # Prompt templates
│   ├── system-prompt.md      # Main system prompt
│   ├── task.md               # Task agent prompt
│   ├── init.md               # Initialization prompt
│   ├── compaction-*.md       # Compaction prompts
│   └── tools/                # Tool-specific prompts

├── core/                     # Core business logic (mode-agnostic)
│   ├── index.ts              # Core exports
│   ├── agent-session.ts      # AgentSession class - THE central abstraction
│   ├── sdk.ts                # SDK wrapper for programmatic usage
│   ├── auth-storage.ts       # AuthStorage class - API keys and OAuth tokens
│   ├── bash-executor.ts      # executeBash() with streaming, abort
│   ├── event-bus.ts          # Event bus for tool communication
│   ├── exec.ts               # Process execution utilities
│   ├── file-mentions.ts      # File mention detection
│   ├── keybindings.ts        # Keybinding configuration
│   ├── logger.ts             # Winston-based logging
│   ├── messages.ts           # BashExecutionMessage, messageTransformer
│   ├── model-registry.ts     # Model registry and configuration
│   ├── model-resolver.ts     # resolveModelScope(), restoreModelFromSession()
│   ├── prompt-templates.ts   # Prompt template loading and rendering
│   ├── session-manager.ts    # SessionManager class - JSONL persistence
│   ├── settings-manager.ts   # SettingsManager class - user preferences
│   ├── skills.ts             # loadSkills(), skill discovery from multiple locations
│   ├── slash-commands.ts     # loadSlashCommands() from ~/.omp/agent/commands/
│   ├── system-prompt.ts      # buildSystemPrompt(), loadProjectContextFiles()
│   ├── terminal-notify.ts    # Terminal notification utilities
│   ├── timings.ts            # Performance timing utilities
│   ├── title-generator.ts    # Session title generation
│   ├── ttsr.ts               # Text-to-speech/speech-to-text utilities
│   ├── utils.ts              # Generic utilities
│   │
│   ├── compaction/           # Context compaction system
│   │   └── index.ts          # Compaction logic, summary generation
│   │
│   ├── custom-commands/      # Custom command loading system
│   │   └── types.ts          # CustomCommand types
│   │
│   ├── custom-tools/         # Custom tool loading system
│   │   ├── index.ts          # Custom tool exports
│   │   ├── types.ts          # CustomToolFactory, CustomToolDefinition
│   │   ├── loader.ts         # loadCustomTools() from multiple locations
│   │   └── wrapper.ts        # Tool wrapper utilities
│   │
│   ├── export-html/          # Session export to HTML
│   │   └── (export logic)
│   │
│   ├── extensions/           # Extension system
│   │   └── (extension loading and execution)
│   │
│   ├── hooks/                # Hook system for extending behavior
│   │   ├── index.ts          # Hook exports
│   │   ├── types.ts          # HookAPI, HookContext, event types
│   │   ├── loader.ts         # loadHooks() from multiple locations
│   │   ├── runner.ts         # runHook() event dispatch
│   │   └── tool-wrapper.ts   # wrapToolsWithHooks() for tool_call events
│   │
│   ├── mcp/                  # MCP (Model Context Protocol) integration
│   │   └── (MCP client/server logic)
│   │
│   ├── plugins/              # Plugin system
│   │   └── (plugin loading and management)
│   │
│   └── tools/                # Built-in tool implementations
│       ├── index.ts          # Tool exports, BUILTIN_TOOLS, createTools
│       ├── ask.ts            # User input tool
│       ├── bash.ts           # Bash command execution
│       ├── bash-interceptor.ts # Bash command interception
│       ├── context.ts        # Tool context utilities
│       ├── edit.ts           # Surgical file editing
│       ├── edit-diff.ts      # Diff-based editing
│       ├── find.ts           # File search by glob
│       ├── gemini-image.ts   # Gemini image generation
│       ├── git.ts            # Git operations
│       ├── grep.ts           # Content search (regex/literal)
│       ├── ls.ts             # Directory listing
│       ├── notebook.ts       # Jupyter notebook editing
│       ├── output.ts         # Output/logging tool
│       ├── read.ts           # File reading (text and images)
│       ├── review.ts         # Code review tools
│       ├── rulebook.ts       # Rulebook tool
│       ├── write.ts          # File writing
│       ├── fetch.ts          # URL content fetching
│       ├── exa/              # Exa MCP tools (22 tools)
│       ├── lsp/              # LSP integration tools
│       ├── task/             # Task/subagent spawning
│       ├── web-search/       # Web search tools
│       ├── path-utils.ts     # Path resolution utilities
│       ├── renderers.ts      # Tool output renderers
│       ├── render-utils.ts   # Rendering utilities
│       └── truncate.ts       # Output truncation utilities

├── modes/                    # Run mode implementations
│   ├── index.ts              # Re-exports InteractiveMode, runPrintMode, runRpcMode, RpcClient
│   ├── print-mode.ts         # Non-interactive: process messages, print output, exit
│   │
│   ├── rpc/                  # RPC mode for programmatic control
│   │   ├── rpc-mode.ts       # runRpcMode() - JSON stdin/stdout protocol
│   │   ├── rpc-types.ts      # RpcCommand, RpcResponse, RpcSessionState types
│   │   └── rpc-client.ts     # RpcClient class for spawning/controlling agent
│   │
│   └── interactive/          # Interactive TUI mode
│       ├── interactive-mode.ts   # InteractiveMode class
│       │
│       ├── components/           # TUI components
│       │   ├── assistant-message.ts    # Agent response rendering
│       │   ├── bash-execution.ts       # Bash output display
│       │   ├── compaction.ts           # Compaction status display
│       │   ├── countdown-timer.ts      # Reusable countdown for dialogs
│       │   ├── custom-editor.ts        # Multi-line input editor
│       │   ├── dynamic-border.ts       # Adaptive border rendering
│       │   ├── footer.ts               # Status bar / footer
│       │   ├── hook-input.ts           # Hook input dialog
│       │   ├── hook-selector.ts        # Hook selection UI
│       │   ├── index.ts                # Component exports
│       │   ├── login-dialog.ts         # OAuth login dialog
│       │   ├── model-selector.ts       # Model picker
│       │   ├── oauth-selector.ts       # OAuth provider picker
│       │   ├── queue-mode-selector.ts  # Message queue mode picker
│       │   ├── session-selector.ts     # Session browser for --resume
│       │   ├── show-images-selector.ts # Image display toggle
│       │   ├── theme-selector.ts       # Theme picker
│       │   ├── thinking-selector.ts    # Thinking level picker
│       │   ├── tool-execution.ts       # Tool call/result rendering
│       │   ├── user-message-selector.ts # Message selector for /branch
│       │   └── user-message.ts         # User message rendering
│       │
│       └── theme/
│           ├── theme.ts      # Theme loading, getEditorTheme(), etc.
│           ├── dark.json
│           ├── light.json
│           └── theme-schema.json

└── utils/                    # Generic utilities
    ├── changelog.ts          # parseChangelog(), getNewEntries()
    ├── clipboard.ts          # copyToClipboard()
    ├── fuzzy.ts              # Fuzzy string matching
    ├── image-convert.ts      # Image format conversion
    ├── image-magick.ts       # ImageMagick integration
    ├── image-resize.ts       # Image resizing utilities
    ├── mime.ts               # MIME type detection
    ├── shell.ts              # getShellConfig()
    ├── shell-snapshot.ts     # Shell state snapshotting
    └── tools-manager.ts      # ensureTool() - download fd, etc.

Key Abstractions

AgentSession (core/agent-session.ts)

The central abstraction that wraps the SDK Agent with:

• Session persistence (via SessionManager)
• Settings persistence (via SettingsManager)
• Model cycling with scoped models
• Context compaction
• Bash command execution
• Message queuing
• Hook integration
• Custom tool loading
• Extension/capability system integration

All three modes (interactive, print, rpc) use AgentSession.

SDK (core/sdk.ts)

Wrapper around @oh-my-pi/pi-agent-core that provides a simplified interface for creating and managing agents programmatically. Used by AgentSession and available as a public API through index.ts exports.

InteractiveMode (modes/interactive/interactive-mode.ts)

Handles TUI rendering and user interaction:

• Subscribes to AgentSession events
• Renders messages, tool executions, streaming
• Manages editor, selectors, key handlers
• Delegates all business logic to AgentSession

RPC Mode (modes/rpc/)

Headless operation via JSON protocol over stdin/stdout:

• rpc-mode.ts: runRpcMode() function that listens for JSON commands on stdin and emits responses/events on stdout
• rpc-types.ts: Typed protocol definitions (RpcCommand, RpcResponse, RpcSessionState)
• rpc-client.ts: RpcClient class for spawning the agent as a subprocess and controlling it programmatically

The RPC mode exposes the full AgentSession API via JSON commands. See docs/rpc.md for protocol documentation.

SessionManager (core/session-manager.ts)

Handles session persistence:

• JSONL format for append-only writes
• Session file location management
• Message loading/saving
• Model/thinking level persistence

SettingsManager (core/settings-manager.ts)

Handles user preferences:

• Default model/provider
• Theme selection
• Queue mode
• Thinking block visibility
• Compaction settings
• Hook/custom tool paths
• Thinking budgets (thinkingBudgets setting for custom token budgets per level)
• Image blocking (blockImages setting to prevent images from being sent to LLM)

Hook System (core/hooks/)

Extensibility layer for intercepting agent behavior:

• loader.ts: Discovers and loads hooks from ~/.omp/agent/hooks/, .omp/hooks/, and CLI
• runner.ts: Dispatches events to registered hooks
• tool-wrapper.ts: Wraps tools to emit tool_call and tool_result events
• types.ts: Event types (session, tool_call, tool_result, message, error, user_bash)

See docs/hooks.md for full documentation.

Extension System Architecture

The extension system uses a shared runtime pattern:

1. ExtensionRuntime (core/extensions/types.ts): Shared state and action handlers for all extensions
2. Extension: Per-extension registration data (handlers, tools, commands, shortcuts)
3. ExtensionAPI: Per-extension API that writes registrations to Extension and delegates actions to runtime
4. ExtensionRunner: Orchestrates event dispatch and provides context to handlers

Key extension events:

• before_agent_start: Receives systemPrompt and can return full replacement (not just append)
• user_bash: Intercept !/!! commands for custom execution (e.g., remote SSH)
• session_shutdown: Cleanup notification before exit

Custom Tools (core/custom-tools/)

System for adding LLM-callable tools:

• loader.ts: Discovers and loads tools from ~/.omp/agent/tools/, .omp/tools/, and CLI
• types.ts: CustomToolFactory, CustomToolDefinition, CustomToolResult

See docs/custom-tools.md for full documentation.

Skills (core/skills.ts)

On-demand capability packages:

• Discovers SKILL.md files from multiple locations
• Provides specialized workflows and instructions
• Loaded when task matches description

See docs/skills.md for full documentation.

Capability System (capability/)

Unified extension system that discovers and loads capabilities from multiple sources:

• Extension Discovery (discovery/): Discovers extensions from Claude.md, .cursorrules, .codex, MCP servers, etc.
• Capability Types: Hooks, tools, context files, rules, skills, slash commands, system prompts, etc.
• Multi-source: Global (~/.omp/), project (.omp/), and built-in capabilities

See docs/extensions.md for full documentation.

Development Workflow

Running in Development

Run the CLI directly with bun (this is a bun-based project):

# From monorepo root
bun run dev

# Or run directly
bun packages/coding-agent/src/cli.ts

# With arguments
bun packages/coding-agent/src/cli.ts --help
bun packages/coding-agent/src/cli.ts -p "Hello"

# RPC mode
bun packages/coding-agent/src/cli.ts --mode rpc --no-session

Type Checking

# From monorepo root (runs biome + tsgo type check)
bun run check

# From packages/coding-agent
bun run check

Building

# Type check and build (from packages/coding-agent)
bun run build

# Build standalone binary
bun run build:binary

Testing

# Run tests (from packages/coding-agent)
bun test

# Run specific test pattern
bun test --testNamePattern="RPC"

# Run RPC example interactively
bun test/rpc-example.ts

Managed Binaries

Tools like fd and rg are auto-downloaded to ~/.omp/bin/ (migrated from ~/.omp/agent/tools/).

Adding New Features

Adding a New Slash Command

1. If it's a UI-only command (e.g., /theme), add handler in interactive-mode.ts setupEditorSubmitHandler()
2. If it needs session logic, add method to AgentSession and call from mode

Adding a New Tool

1. Create tool factory in core/tools/ following existing patterns (e.g., createMyTool(session: ToolSession))
2. Export factory and types from core/tools/index.ts
3. Add to BUILTIN_TOOLS map in core/tools/index.ts
4. Add tool prompt template to prompts/tools/ if needed
5. Tool will automatically be included in system prompt

Adding a New Hook Event

1. Add event type to hook event types in core/hooks/types.ts
2. Add emission point in relevant code (AgentSession, tool wrapper, etc.)
3. Update docs/hooks.md with the new event type

Adding a New RPC Command

1. Add command type to RpcCommand union in modes/rpc/rpc-types.ts
2. Add response type to RpcResponse union in modes/rpc/rpc-types.ts
3. Add handler case in handleCommand() switch in modes/rpc/rpc-mode.ts
4. Add client method in RpcClient class in modes/rpc/rpc-client.ts
5. Update docs/rpc.md with the new command

Adding a New Selector

1. Create component in modes/interactive/components/
2. Use showSelector() helper in interactive-mode.ts:

private showMySelector(): void {
    this.showSelector((done) => {
        const selector = new MySelectorComponent(
            // ... params
            (result) => {
                // Handle selection
                done();
                this.showStatus(`Selected: ${result}`);
            },
            () => {
                done();
                this.ui.requestRender();
            },
        );
        return { component: selector, focus: selector.getSelectList() };
    });
}

Adding a New Extension Source

1. Create discovery module in discovery/ (e.g., my-source.ts)
2. Implement discovery functions that return capability objects
3. Add to discovery chain in discovery/index.ts
4. Update docs/extension-loading.md with the new source

Adding a New Capability Type

1. Create capability module in capability/ (e.g., my-capability.ts)
2. Define capability type and schema
3. Add to capability registry in capability/index.ts
4. Add loader/handler in relevant core module
5. Update docs/extensions.md with the new capability type

Adding a New Keybinding

1. Add the action name to AppAction type in core/keybindings.ts
2. Add default binding to DEFAULT_APP_KEYBINDINGS
3. Add to APP_ACTIONS array
4. Handle the action in CustomEditor or InteractiveMode

Example: The dequeue action (Alt+Up) restores queued messages to the editor.

Code Style

• TypeScript with strict type checking (tsgo)
• No any types unless absolutely necessary
• No inline dynamic imports
• Formatting via Biome (bun run check or bun run fix)
• Keep InteractiveMode focused on UI, delegate logic to AgentSession
• Use event bus for tool/extension communication
• Components should override invalidate() to rebuild on theme changes

Package Structure

This is part of a monorepo with the following packages:

• @oh-my-pi/pi-coding-agent (this package) - Main CLI and TUI
• @oh-my-pi/pi-agent-core - Core agent implementation
• @oh-my-pi/pi-tui - TUI components
• @oh-my-pi/pi-ai - External AI provider library

CLI Flags

Key CLI flags for development:

• --no-tools: Disable all built-in tools (extension-only setups)
• --no-extensions: Disable extension discovery (explicit -e paths still work)
• --no-skills: Disable skill discovery
• --session <id>: Resume by session ID prefix (UUID match) or path

SDK Exports

The SDK (src/index.ts) exports run modes for programmatic usage:

• InteractiveMode: Full TUI mode
• runPrintMode(): Non-interactive, process messages and exit
• runRpcMode(): JSON stdin/stdout protocol

Extension types and utilities are also exported for building custom extensions.

Documentation

See the docs/ directory for detailed documentation:

• docs/sdk.md - SDK usage and examples
• docs/rpc.md - RPC protocol documentation
• docs/hooks.md - Hook system documentation
• docs/extensions.md - Extension system documentation
• docs/custom-tools.md - Custom tool development
• docs/skills.md - Skill system documentation
• docs/compaction.md - Context compaction system
• docs/session.md - Session management
• docs/theme.md - Theme customization
• docs/tui.md - TUI architecture