feat: add daemon mode for persistent MCP connections

[cs50victor]

adds a persistent connection daemon that keeps MCP server processes alive across CLI invocations, enabling stateful workflows without reconnection overhead.

• mcp-cli daemon start|stop|status - manage daemon lifecycle
• Tool calls auto-route through daemon when running
• Falls back to ephemeral mode when daemon is not running
• Idle timeout evicts unused connections (default: 5 min)

CLI invocation -> Unix socket -> Daemon -> MCP Server Pool

• MCP_DAEMON_SOCKET - Socket path (default: ~/.mcp-cli/daemon.sock)
• MCP_DAEMON_IDLE_MS - Idle timeout in ms (default: 300000)

tested

• bun run lint passes
• bun run typecheck passes
• bun run test passes (120/122, 2 pre-existing failures)
• Manual test: daemon start/stop/status
• Manual test: stateful persistence with chrome-devtools-mcp

Before vs After

Scenario	Without Daemon	With Daemon
navigate_page → list_pages	Second call sees about:blank (new browser)	Second call sees navigated URL (same browser)
Multi-step workflow	Each tool call spawns fresh MCP server	All calls share persistent connection
Connection overhead	Full server startup per invocation	One-time startup, reused across calls
Stateful MCP servers	Broken (state lost between calls)	Works as expected

Concrete example with chrome-devtools-mcp:

# WITHOUT DAEMON
mcp-cli chrome/navigate_page '{"url": "https://example.com"}'  # → Success
mcp-cli chrome/take_screenshot '{}'                            # → Screenshots about:blank (new instance)

# WITH DAEMON
mcp-cli daemon start
mcp-cli chrome/navigate_page '{"url": "https://example.com"}'  # → Success
mcp-cli chrome/take_screenshot '{}'                            # → Screenshots example.com (same instance)

[philschmid]

Interesting idea, but i didn't want to add a daemon as it adds a new command which the mode needs to understand and manage. Did you test your branch? What is the impact of it?

[cs50victor]

@philschmid I tested this PR with a few MCPs I use alongside Claude Code, such as chrome-devtools-mcp. It fixes the issue of state not being preserved between tool calls, which is necessary for chaining tool calls in complicated browsing tasks - for example, opening a page, taking a screenshot, navigating to a URL, then clicking a link on the page. If you'd like me to refactor this PR or make any changes to the API, I'm open to doing so.

[philschmid]

Interesting MCP servers should be stateless by default. Is the chrome dev tool not stateless? If we want to add this we also need to update hte readme, skill and SI. Can you look at this as well? Once we have all of that i will test it too.

[cs50victor]

i've also updated the pr description with commands to reproduce the error i was facing.

[cs50victor]

hey @philschmid let me know if there are any changes to make so this goes in.

[philschmid]

Hey thank you for the PR. I did some experiments myself and added Daemon support in 0.3.0 full changes here: https://github.com/philschmid/mcp-cli/blob/main/CHANGELOG.md#030---2026-01-22

The Daemon is lazy meaning the first request creates a connection which is hold for 60s (configurable) and is reused for the next request.

[cs50victor]

nice. that's a much more efficient design.