Cursor adds event subscriptions, custom modes, and subagent VMs for cloud agents

Cursor's update lets cloud agents subscribe to PRs, Slack threads, and scheduled tasks, and wake when something happens. It also adds custom modes that pin a skill in chat, subagents that run on their own virtual machines, and a /goal command for long-lived objectives. Users can also send steering messages while an agent works, with follow-ups applied at the next tool call.