Ask anyone who has shipped software where the quality leaked out, and they will point at the same place: the handoff. The moment a finished design crosses the wall to engineering, and everything that made it good becomes negotiable.
The spacing drifts. The empty states vanish. The loading behavior gets invented on the spot by whoever wrote the component, at 6pm, without the context. None of this is malice. It is what happens when the person who understood the decision is not the person implementing it.
Documentation is not the fix
The industry’s answer has been thicker handoffs. Redlines, spec tools, fifty-page component documentation, recorded walkthroughs. All of it helps and none of it works, because documentation is a lossy format for judgment. You can write down what the design is. You cannot write down everything it is not, and implementation is mostly a series of encounters with cases the mockup never covered.
Every one of those encounters is a design decision. If the designer is not there, the decision still gets made. Just not by design.
One team, or one person
Our answer is structural, not procedural: the person who designs a flow sits inside the build of it, and often is the builder. Design reviews happen in the running product, not in the mockup. When an edge case surfaces on Tuesday, it is designed on Tuesday, in code.
This is not a plea for unicorns. It is a team shape. Small, senior, and accountable for the shipped thing rather than the artifact that described it.
A design is a prediction. The product is the result. Accountability belongs to the result.
The pleasant side effect is speed. The handoff was never just a quality leak, it was the schedule’s slowest bridge. Remove it and weeks come back.