When an agent spawns a subagent, opening the subagent in a new tab before it starts causes the tab to remain stuck in an empty state. Additionally, the subagent preview in the parent agent is incorrectly marked as completed, while the subagent continues running in the background.
Steps to Reproduce
Prompt a parent agent to spawn a subagent (for example: “spawn a subagent for testing”).
As soon as the subagent preview appears, quickly click it to open the subagent in a new tab.
Subagent tab remains in an empty state, while the subagent preview in the parent agent is immediately marked as completed.
Hey, thanks for the detailed report with the video and steps, that really helps.
There are two separate behaviors here:
Empty tab if you click during Starting up: if you click the subagent card while it’s still in the warm-up phase, it opens an empty tab that never picks up the running subagent. Workaround: wait until the subagent shows active progress, then open it. Clicking specifically during Starting up is what causes the empty tab. We fixed something similar before, and it looks like it came back in 3.7.27, I’ve reported it internally as a regression.
The subagent preview shows Completed even though it’s still running: this is a known display bug and it’s already being tracked. The subagent itself keeps running correctly in the background.
I can’t share an exact ETA for a fix yet. If anything changes after updates or you notice something new, please post here.
The first of the two sometimes causes the subagent to stop (different from “failed to start”) for me. It jus shows the same thing it would if i manuly hhit theh stop button on the subagent. Its not always theh case tho.
Hey, thanks for adding details. The fact that clicking during the Starting up phase sometimes fully stops the subagent, and not just opens an empty tab, looks like another version of the same early-click race. The main early-open bug is already reported internally, and I’ll flag this stopping symptom too.
For now, the workaround is the same: wait until the subagent shows active progress, then open the card. Clicking specifically during Starting up is what triggers the issue.
To help us dig into the stopping behavior, can you share:
your Cursor version and OS
the Request ID if you catch it when it stops right top chat menu > Copy Request ID
how often it happens, like every Nth time or very rarely
No ETA for a fix yet. If you notice anything new, post it here.
Hey @luthfihizb, circling back on this thread. You’re on a pretty recent version now. Do you still see an empty subagent tab if you open the subagent card right away during the “Starting up” phase?
The workaround is the same. Wait until the subagent shows active progress, then open the card. Clicking during “Starting up” is what triggers the issue.
If a recent update fixed it, let me know. If not, details would help. The exact version, and confirmation that waiting for progress before opening still works around it.
cc @JakobPCoder, for your case where the subagent fully stops. If you catch it happening, please share the Request ID (chat menu in the top right > Copy Request ID) and how often it happens.
