Expose active MCP servers/plugins in statusLine input JSON

Feature Request

Is your feature request related to a problem?

The statusLine command receives a JSON object on stdin with useful session state (context window usage, model, cost, workspace), but there's no information about which MCP servers or plugins are currently connected and active in the session.

As a user with multiple MCP servers configured (e.g., GitLab, custom tools), I'd like to see at a glance which ones are actually connected in my current session — directly in my status line.

Describe the solution you'd like

Add an mcp (or plugins) field to the statusLine input JSON, e.g.:

{
  "mcp": {
    "servers": [
      { "name": "gitlab", "status": "connected" },
      { "name": "my-custom-server", "status": "connected" }
    ]
  }
}

This would allow statusLine scripts to display which MCP servers are active, how many are connected, or flag any that have disconnected.

Describe alternatives you've considered

• Running /doctor or claude mcp list manually, but these are not integrated into the persistent status line display.
• Hardcoding server names from .mcp.json / settings.json, but this doesn't reflect actual runtime connection status.