A background subagent finishes an investigation, and an hour later a follow-up question about its findings comes up. What does Cursor make possible?

The principle — Each subagent execution returns an agent ID, and background subagents write their state to disk as they go. A finished subagent is a conversation you can pick up again, rather than a call that has already returned.

Why the key is correct — Passing that ID back resumes the subagent with its context intact, so the follow-up lands on an agent that already knows the paths, the dead ends and the findings.

Why the others are wrong — Starting fresh is possible but wasteful, since completion does not discard the state. Re-issuing the original prompt reproduces neither the exploration nor the saving. And the state is persisted rather than held in memory, so the returned summary is far from all that survives.

Remember this — Keep the agent ID; a completed subagent resumes with its context.

Sources — Cursor's Subagents documentation.