I cannot create a summary of the requested article because it is not found in the search results provided. The search results contain articles on proteostasis from a variety of sources, including studies on proteostasis in aging, prostate cancer, and inhibitor resistance mechanisms, but the specific article "Systems-level organization of extracellular proteostasis" from the journal Science, Volume 391, Number 6792, March 2026 is not among them. In order to create an accurate and factual summary as per your requirements, I would need access to the full text of this particular article.