Hi John,
you will need to use the “hot mode” for psh:
./psh.phar storefront:hot-proxy
Then you will be able to see sourcemaps:
https://github.com/shopware/platform/blob/66fd12c4e63f0641a724ed10bfd5e55553bd1d1c/src/Storefront/Resources/app/storefront/build/webpack.hot.config.js#L75
Kind regards,
Tim