tl;dr: AI agents have dramatically lowered the cost of personalizing software—you can now prompt an agent to modify source code and automatically rebase your changes against upstream releases, making bespoke tooling practical for individuals and small teams. This shifts the value away from plugin systems and configuration APIs toward direct source modification, which means devtools must be open source to remain competitive. Closed-source tools like Claude Code hit a wall here, while open agents like Codex or Pi can be personalized freely.