This is a known bug. The AppArmor profile shipped with Cursor doesn’t include signal rules, so on Ubuntu 24.04+ (which enables signal mediation by default), signals from outside the sandbox boundary get blocked. Your workaround is exactly right.
Our team is tracking this and working on updating the profile. In the meantime, there are a few other options if you hit a stuck process:
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Kill the parent bwrap process (it’s in the host namespace, so it’s killable):
pkill -9 bwrap -
Close the terminal tab in Cursor that started the process.
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Restart Cursor — all sandboxed processes will be cleaned up on exit.
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Disable the sandbox temporarily: Cursor Settings > Agents > Sandbox (removes the isolation layer entirely).
There’s also more discussion on this in a related thread. We will update that thread with the latest information, closing this one to ensure it’s well tracked.