feature: Native IDE Integration via ACP/MCP Protocol

[JanSmrcka]

Did you check the docs?

• I have read all the sidekick.nvim docs

Is your feature request related to a problem? Please describe.

When using sidekick.nvim to launch AI coding CLI tools (Claude Code,
Gemini CLI, Codex, etc.), they don't detect Neovim as an IDE. The
/ide command in Claude Code shows no connected IDE, even when running
inside a Neovim terminal buffer.

This means features like automatic file context sharing, selection
tracking, and native diff viewing don't work - users only get basic
terminal interaction.

Modern AI CLI tools use protocols (MCP/ACP) to communicate with IDEs:

• MCP (Model Context Protocol) - Used by Claude Code, Gemini CLI
• ACP (Agent Client Protocol) - Supported by Claude Code, Codex CLI,
  Gemini, goose

Both work by having the editor run a local WebSocket/HTTP server and
writing a discovery file that CLI tools find on startup.

Describe the solution you'd like

Native IDE integration in sidekick.nvim via MCP and/or ACP protocol
support.

When enabled, sidekick would:

1. Start a WebSocket/HTTP server on a random port using vim.loop
2. Write a lock file (e.g., ~/.claude/ide/[port].lock) with connection
   metadata
3. AI CLI tools automatically discover and connect to Neovim
4. Expose editor context (open files, selections, diagnostics) via
   JSON-RPC 2.0

Configuration example:

opts = {
  cli = {
    ide_integration = {
      enabled = true,
      protocol = "mcp", -- or "acp" or "both"
    },
  },
}

This would make sidekick a complete solution for AI coding assistants -
UI, keybindings, AND IDE integration in one plugin.

Describe alternatives you've considered

1. Using coder/claudecode.nvim alongside sidekick

Current workaround - install claudecode.nvim with provider = "none"
(WebSocket server only, no UI), and use sidekick for the interface:

{
   "coder/claudecode.nvim",
   opts = {
     terminal = { provider = "none" },
     auto_start = true,
   },
 },
 { "folke/sidekick.nvim", ... }

This works but requires two plugins for what should be integrated
functionality.

2. Using only coder/claudecode.nvim

Loses sidekick's superior UI, keybindings, and multi-tool support.

3. Manual /ide connection

Running claude --ide tries to connect but picks VS Code over Neovim if
both are available, since Neovim isn't officially detected without the
WebSocket server.

---

References:

• https://github.com/coder/claudecode.nvim - Working pure-Lua MCP
  implementation
• https://block.github.io/goose/blog/2025/10/24/intro-to-agent-client-protocol-acp/
• https://geminicli.com/docs/ide-integration/ide-companion-spec/

Additional context

No response

[sebastianstudniczek]

Guess it's not planned, at least for now #55