Home Assistant stops removing a device’s setup card while someone is entering its pairing code. Bluetooth devices can stop advertising as soon as a connection begins, so pairing itself could make the device disappear and end setup with an invalid-flow error.
J. Nick Koston extends the protection for an active setup to Bluetooth and SSDP network discovery. A device explicitly reporting that it is already paired still ends the attempt, and unplugged USB devices retain their existing behavior.