Clearer warning when the desktop app overrides a settings env var

Your settings file can set environment variables, named values that programs read, for Claude Code. When a session is started by the desktop app or a runner that already supplies one of those values, Claude Code shows a warning. The warning now says that the desktop app or runner that started the session supplies the value, so the value in your settings is not used. Before, it said the environment the session was launched with already set it.