MCP servers

config/mcp.json lists the MCP servers a session can turn on, in pi’s format. Servers authenticate with headers. In a header, ${GITHUB_TOKEN} is the session’s GitHub token, the one it uses for git, limited to its repository and renewed on every dispatch, so GitHub’s MCP server needs no token of its own:

{
  "mcpServers": {
    "github": {
      "url": "https://api.githubcopilot.com/mcp/",
      "headers": {
        "Authorization": "Bearer ${GITHUB_TOKEN}",
        "X-MCP-Tools": "issue_read,list_issues,search_issues,..."
      }
    }
  }
}

A turn’s mcp lists the servers to turn on, from mcp.json or registered by an extension with pi.registerMcpServer(). The session keeps the list until a turn sends another, and subagents use it:

rebuno exec create uber '{"task": "Triage the open issues.", "mcp": ["github"]}' --session triage

Each server’s tools are named mcp__<server>__<tool> and run as recorded steps under policy. A server’s tool list is recorded too, so a replay builds the same prompt without connecting.

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