> ## Documentation Index
> Fetch the complete documentation index at: https://docs.mains.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# Configuration

The Cursor agent runtime in Mains uses the **Cursor Agent CLI** (the `agent` binary) and communicates with it over the **Agent Client Protocol (ACP)** via stdio. These settings control authentication, model selection, and how the agent operates during runs.

## **Installation & Authentication**

Mains drives the Cursor Agent CLI as a subprocess. You must install and authenticate the CLI before using it inside Mains.

<Steps>
  <Step title="Install the Cursor Agent CLI">
    Run the official installer in your terminal:

    ```bash theme={null}
    curl https://cursor.com/install -fsS | bash
    ```
  </Step>

  <Step title="Authenticate">
    Launch the CLI once to log in with your Cursor account:

    ```bash theme={null}
    agent
    ```

    Follow the browser prompt to complete authentication. Mains reuses these credentials automatically.
  </Step>

  <Step title="Open Mains">
    Open a Cursor workspace from the sidebar. Mains spawns the CLI on demand and connects via ACP.
  </Step>
</Steps>

<Note>
  Need help with the CLI itself? See the official [**Cursor CLI Setup Guide**](https://docs.cursor.com/en/cli/overview).
</Note>

## **Mode**

The mode controls how Cursor behaves during runs. You set it once in **Settings > Cursor**, and Mains applies it to every session.

| **Mode** | **Description**                                                                                      |
| -------- | ---------------------------------------------------------------------------------------------------- |
| `agent`  | Full autonomous agent mode -- Cursor plans and executes tool calls automatically (default).          |
| `plan`   | Plan first, then execute -- Cursor produces a plan and pauses for confirmation before taking action. |
| `ask`    | Answer-only mode -- Cursor responds to questions but does not invoke tools or modify files.          |

<Note>
  Pulse-driven runs always force `agent` mode regardless of your default. This guarantees scheduled tasks can complete autonomously without human input.
</Note>

## **Model Selection**

Cursor exposes the list of available models through ACP after a session starts. Mains picks them up automatically and lets you choose a default model in settings.

When you start a run, Mains sends `session/set_config_option` with your preferred model. If the model is unavailable, the session falls back to Cursor's default for your account.

| **Behavior**      | **Description**                                                                      |
| ----------------- | ------------------------------------------------------------------------------------ |
| **Default model** | Applied to every new session unless overridden per run.                              |
| **Per-run model** | Set on individual runs to test different models without changing your default.       |
| **Resume**        | When you continue a previous session, Mains re-applies your model and mode settings. |

## **MCP Tools**

Cursor sessions automatically receive Mains' bundled MCP tools at startup -- these include git operations, package safety checks, and workspace utilities. You can also add your own MCP servers; see [**<u>MCP Servers</u>**](/mcp-servers) for setup.

Cursor extensions like `update_todos`, `generate_image`, and the task subagent are exposed as native ACP capabilities, not MCP tools.

## **Tool Approval**

Cursor sends a `session/request_permission` ACP request when it wants to invoke a tool that requires user confirmation. Mains shows an interactive approval dialog in the workspace UI -- you can allow once, deny, or remember the decision for the session.