feature: Add support for the Pi coding agent

[Rom888]

Prerequisites

• I searched the docs
• I searched existing issues

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

I use both the Pi coding agent and OpenCode and would like to use the polished Neovim UI provided by opencode.nvim with Pi too. Currently, opencode.nvim is tied to OpenCode, while Pi users need to use a separate Neovim integration with a more minimal UI.

Describe the solution you'd like

Add support for the Pi coding agent as another backend/agent that can be used with opencode.nvim's UI.

There is already a Neovim plugin for Pi, carderne/pi-nvim, which provides a similar integration, but with a much more minimal UI.

Describe alternatives you've considered

Using carderne/pi-nvim is the main alternative I've considered. It works with Pi, but I would prefer to use the more polished UI and features of opencode.nvim.

Additional context

No response

[nickjvandyke]

Glad you like opencode.nvim's interface this much! 🙂 I'm feeling this too but with Claude because it's what my new job provides.

Unfortunately other harnesses seem to have worse APIs. Custom plugins could maybe expose the necessary endpoints. But that practically doubles the work and maintenance.

How much of OpenCode's API does Pi already expose?

[Rom888]

Pi doesn't expose OpenCode's API directly, so I wouldn't describe it as exposing a percentage of it. However, I think Pi already has a good foundation for the kind of integration that opencode.nvim provides.

There is pi --mode rpc but it is a different thing: it runs Pi headlessly and exposes an RPC protocol over stdin/stdout.

carderne/pi-nvim instead works with the normal interactive Pi process:

Pi TUI
   │
   ├── normal terminal UI
   │
   └── pi-nvim extension
          │
          │ Unix socket
          ▼
       Neovim

The extension runs inside the existing Pi process and has access to its agent/session. Neovim communicates with that extension over the Unix socket. So Pi keeps its normal TUI, while Neovim acts as an additional client of the same running Pi session.

I'd envision opencode.nvim using the same general architecture, but with a richer IPC protocol:

                         ┌─────────────────────┐
                         │      Pi TUI         │
                         │                     │
                         │    AgentSession     │
                         │          │          │
                         │   opencode.nvim     │
                         │      extension      │
                         │          │          │
                         └──────────┼──────────┘
                                    │
                              Unix socket /
                                IPC API
                                    │
                                    ▼
                         ┌─────────────────────┐
                         │    opencode.nvim    │
                         │      Neovim UI      │
                         └─────────────────────┘

The existing pi-nvim protocol is quite minimal, though. It essentially provides things such as sending prompts and pinging the Pi process.