Cursor SDK 1.0.31 lets you steer a running agent mid-turn and swap its system prompt

In @cursor/sdk 1.0.31, run.steer(text) injects a message into the turn in flight (a running foreground subagent moves to the background and keeps going), custom tools can carry MCP annotations like readOnlyHint and destructiveHint, and systemPrompt on Agent.create() replaces Cursor's built-in prompt while rules and skills still load. Steering and the prompt swap are TypeScript local agents only, cloud runs return revert_to_followup, and systemPrompt is enabled per account, so it fails on first send() until yours is on.