A Docker Compose application could use ${VAR} as a network name, but
only services created the variable. With ${VAR:-default} the value was
hidden and could not be edited; with ${VAR} Compose got an empty name
and the deployment failed. Applications now get the variable (and its
preview copy) with the default from the compose file, like services.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
