Complete the remaining M8 extensibility deliverables:
- MCP client with JSON-RPC 2.0 over stdio transport, protocol
lifecycle (initialize/tools-list/tools-call), and process group
management for clean shutdown
- MCP tool adapter implementing tool.Tool with mcp__{server}__{tool}
naming convention and replace_default for swapping built-in tools
- MCP manager for multi-server orchestration with parallel startup,
tool discovery, and registry integration
- Plugin system with plugin.json manifest (name/version/capabilities),
directory-based discovery (global + project scopes with precedence),
loader that merges skills/hooks/MCP configs into existing registries,
and install/uninstall/list lifecycle manager
- Config additions: MCPServerConfig, PluginsSection with opt-in/opt-out
enabled/disabled resolution
- TUI /plugins command for listing installed plugins
- 54 tests across internal/mcp and internal/plugin packages