[Bug] Connecting to Prime Hub while program runs crashes hub on exit

[laurensvalk]

Describe the bug

Connecting to Prime Hub while program runs crashes hub on exiting that program.

To reproduce

from pybricks.tools import wait

while True:
    wait(50)
    print("Hello, world!")

• Run it on a Prime Hub
• Disconnect
• Run it on a Technic Hub
• Disconnect
• Connect to Prime Hub again (shouldn't be possible, but you can).
• Pybricks Code gets in bad state (BT connected, but not stop button)
• Cancel Prime Hub program with button
• Hub freezes (animation freeze) then turns off.

Expected behavior
Perhaps fail to connect or something like it, but not crash on exit.

Screenshots
Reproducing it:

untitled.mp4

[laurensvalk]

The above procedure always crashes, but here's a way you can sometimes do it on one Prime Hub:

• Run this program: https://github.com/pybricks/pybricks-api/blob/master/examples/pup/motor/motor_action_basic.py
• Disconnect after starting it
• Connect again while it is still running

[dlech]

This is fixed by not allowing Pybricks Code to reconnect to the hub while a user program is running (which is the intended behavior). There is a "feature" in BTStack that automatically started advertising again after disconnect, which was unexpected.