Software design documents in 2026, who writes them now?

AI coding agents generate production code, write test suites, and review pull requests with enough accuracy that most engineering teams trust the output for a meaningful share of their implementation work. The downstream side of the development lifecycle, everything after the decision of what to build and how, got dramatically faster this year. The upstream side barely moved. Software design documents, the artifacts where feasibility analysis, service boundaries, dependency mapping, and implementation approach get captured, still depend entirely on one or two senior engineers who carry the system's mental model. That work consumes 60 to 70% of their time, and the entire team queues behind them before a single line of code gets written. The pre-coding bottleneck that AI skipped over Every new feature follows the same sequence. Someone creates a Jira ticket. A senior engineer or architect reads it and starts answering the hard questions. Can this be built on top of our current service to