Cursor adds background subagent reporting and tool annotations; custom system prompts roll out account by account

Cursor says background subagents now return results to the parent in a follow-up turn on the same run, with stream() and wait() continuing until all finish. Custom tools can carry MCP annotations such as readOnlyHint and destructiveHint, which Cursor says let the model distinguish a lookup from a delete before calling a tool. Users can also replace Cursor's system prompt while rules, skills and tool schemas still load; Cursor says it's enabling this account by account.