Working inside a side chat opened off a long investigation, a developer types `/side` again to branch the exploration further. What happens?

The principle — A side chat is a durable child conversation attached to one parent agent, and that attachment is exactly one level deep. Cursor does not support nesting: a side chat cannot spawn a side chat of its own, and new ones are started from the parent conversation instead.

Why the key is correct — Asking for a side chat from inside a side chat produces no grandchild thread. Every branch of the exploration therefore hangs off the same parent and is seeded with the parent history, which matters in practice: the reasoning you built up inside the first side chat is exactly what the next branch will lack. A tree of explorations has to be planned as a flat fan-out, and anything worth carrying forward should be brought back into the parent first, by @-mentioning the side chat there.

Why the others are wrong — No child thread opens beneath the current one, so there is no mechanism that would pass the side chat's own transcript downwards. The request is also not quietly converted into a fork; forking is a distinct feature that copies the parent conversation wholesale, including its subagents. And the existing thread is left alone rather than reset, because a side chat is durable and survives until you close it to archive it.

Remember this — Side chats fan out from the parent; they do not stack.

Sources — Cursor's Side chats documentation.