Docker Compose merges port lists from multiple -f files by concatenation.
Without !reset, both 0.0.0.0:8000:8000 (base) and 127.0.0.1:8000:8000
(prod override) are applied simultaneously, causing "port already allocated".
!reset clears the list before applying prod-specific bindings (requires
Docker Compose v2.24+, available in current docker-compose-plugin via apt).
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>