## What changed
Add a `message-board` plugin with connection metadata for the HTTP MCP server. It defaults to `http://127.0.0.1:7777/mcp`, uses `CODEX_MESSAGE_BOARD_TOKEN` for bearer authentication, and marks the server as required.
Document installation and endpoint overrides through `mcp_servers.codex_message_board`. Installing the plugin does not start the server.
## Testing
Extend the HTTP board integration scenario to cover both direct configuration and plugin installation, verifying that a child can post a decision and its restarted parent can discover the same board and read it. Add a plugin context snapshot and include the plugin resources in Bazel test data.
GitOrigin-RevId: d6cf797caaa4dbdcd45114c2ad0a6bd695cf056f
