MCP env overrides in CODEX_CONFIG get dropped when a session adds another MCP server

[ruixingshi]

Hi! In codex-acp 1.10.0, adding an MCP server through session/new.mcpServers drops existing MCP settings from CODEX_CONFIG, even when the names don’t overlap.

For example, my app uses CODEX_CONFIG to give Codex’s existing browser tool a proxy:

{
  "mcp_servers": {
    "node_repl": {
      "env": {
        "HTTPS_PROXY": "http://127.0.0.1:7890"
      }
    }
  }
}

If the session also includes an unrelated docs MCP server, the adapter’s outgoing config only contains docs—the browser’s proxy settings disappear. With an empty session MCP list, they stay.
Adding a docs tool shouldn’t remove the browser’s network settings.

createSessionConfig() replaces the whole mcp_servers object. Could it merge entries by server name instead, preserving those that don’t conflict?