When using a custom Docker Compose build command, environment variables
were being lost because the --env-file flag was not included. This fix
automatically injects the --env-file flag to ensure build-time environment
variables are available during custom builds.
Changes:
- Auto-inject --env-file /artifacts/build-time.env after docker compose
- Respect user-provided --env-file flags (no duplication)
- Append build arguments when not using build secrets
- Update UI helper text to inform users about automatic env injection
- Add comprehensive unit tests (7 test cases, all passing)
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
