Sure, but most engineers are working for a business and most businesses don't have perfect processes. I think we can say (1) engineering productivity is severe

Sure, but most engineers are working for a business and most businesses don't have perfect processes. I think we can say (1) engineering productivity is severely impeded by interruptions and (2) it doesn't hurt to work on skills to help yourself get less impacted by disruptions. You're right there's no secret technique, but documenting your work and thoughts, keeping TODO lists, breaking down large work items into small chunks can all help distractions not ruin your day. But, these are effectively "hacks" and the only way to ensure highest possible productivity is to have processes which prevent engineers from being interrupted