You're mixing up design and manufacturing. A skyscraper is first completely designed (on paper, cad systems, prototypes), before it is manufactured. In software engineering, coding is often more a design phase than a manufacturing phase.

Designers need malleability, that is why they all want digital design systems.

Yep! Manufacturing is the running of the software, either via testing or via deployment. That’s when you’ll find bugs or design defects. Operational errors (misconfigurations, under allocation of resources) are not related to the design of the software itself.

Splitting coding and design is a bad idea. It’s like asking engineers not to draw and measure.