feat: Adds support for Cursor provider and other ACP backends

[aweis89]

Summary

• While ACP is already supported for custom IDE integrations (IDE/ACP-> OpenCode -> LLM), this adds support to use ACP as a backend LLM provider (OpenCode -> ACP)
• Enables OpenCode to consume tokens from Cursor CLI for example while still using the regular OpenCode TUI.
• This is useful for folks who have Cursor subscriptions for example, but want to use OpenCode's (amazing!) TUI
• By enabling ACP as a backend provider, we don't need a uniq translation layer for OpenCode to multiple CLI backends

Resolves

• Closes #3735 - CLI Providers feature request
• Closes #2072 - Support for Cursor CLI
• Closes #402 - Gemini CLI support for free tier access
• Closes #5182

Implementation Details

Core Components

1. ACPClient (client.ts) - Manages subprocess lifecycle and ACP protocol communication
2. ACPLanguageModel (model.ts) - Implements LanguageModelV2 interface with streaming support
3. Message Converters (converters.ts) - Bidirectional conversion between Vercel AI SDK and ACP message formats
4. MCP Converter (mcp-converter.ts) - Converts OpenCode MCP configurations to ACP format
5. Provider Factory (factory.ts) - Creates ACP provider instances from configuration

Key Features

• Full streaming support for real-time responses
• Tool execution, passes along MCP servers, which are executed by the ACP
• MCP server integration - OpenCode MCP servers exposed to ACP backends
• Proper subprocess lifecycle management and cleanup
• Comprehensive error handling

Testing

• Tested with cursor-agent integration
• Verified streaming responses
• Confirmed MCP server exposure to ACP backend

Documentation

• Added comprehensive README.md with setup instructions
• Includes configuration examples for cursor-agent, goose, and gemini-cli
• Documents architecture and design decisions

[rekram1-node]

we already have acp support, whats this for

[aweis89]

we already have acp support, whats this for

This is for an ACP backend provider. For example, if you have a cursor account, and you want to use Opencode TUI's interface, but you want it to use cursor CLI agent as it's backend LLM:

Right now we have: IDE via ACP -> OpenCode -> LLM Provider With this change you can now do: OpenCode -> Cursor CLI via ACP The ACP becomes the LLM provider as apposed to the frontend interface. This is useful for folks who want to use OpenCode but already have a subscription for cursor. They can now use OpenCode while comsuming their tokens from Cursor

[rekram1-node]

okay i see

[aweis89]

okay i see

Been using this all morning. It's pretty awesome to be able to use my Cursor subscription with OpenCode's best-in-class TUI!

[aweis89]

[aweis89]

Any chance this is something we can merge @rekram1-node?