Architecture a client can read without a developer

Architecture is often kept in the team's head. Six months later nobody remembers why the queue is there, or why a report is calculated at night instead of on a button. We leave one page: which parts the system has, where the data sits, which outside services are connected, and what happens if one of them stops. No UML layers, and no words that only the author of the diagram needs. The page is not there to defend a decision. It is there so the next person — your developer or ours — can change the product instead of reconstructing it from a thread of messages.