[JKCalhoun]

> they ought to collaborate on its design and implementation from the start

That's exactly right. After said process, it comes down to trusting your coworkers to execute capably. And if you don't think coworker is capable, say so (or if they're junior, more prudently hand them the simpler tasks — perhaps code review behind their back and let it go if the code is "valid" — even if it is not the Best Way™ in your opinion.)