callx is a Node.js CLI tool that serves as a unified runtime switcher and configuration manager for AI coding assistants like Claude Code and OpenCode. It allows users to define multiple AI 'sprites' (agent configurations) with different providers, models, skills, and MCP servers, all managed through a single `~/.config/callx` directory. The system provides two entry points: the `call` command for quick invocation of sprites, and `callcli`, a full-featured TUI built with Ink and React for managing providers, sprites, skills, MCP servers, and git worktrees. The architecture is a monolith CLI application with a clear separation between runtime utilities (`lib/runtime.js`), git worktree helpers (`lib/worktree.js`), and the TUI frontend (`lib/callcli/app.mjs`). The runtime module handles all configuration file I/O, provider normalization, skill syncing via symlinks, and MCP server configuration generation for both Claude Code and OpenCode formats. The TUI provides a Monokai-themed interface with list-based navigation, field-level editing, and multi-select for skills and MCP servers. Key data flows include: reading `providers.json` for API keys and endpoints, reading sprite `config.json` for CLI type and model selection, syncing skill packs from `skillpacks/` to sprite-specific `skills/` directories via symlinks, and generating MCP configuration files from `mcpservers/` definitions. The tool also integrates with git worktrees, providing an interactive flow to create new branches and worktrees with suggested naming conventions. External dependencies are minimal: Node.js 18+, Ink and React for the TUI, and the target AI CLI tools (opencode-ai, @anthropic-ai/claude-code).