How to handle the kernel debugger?

Suddenly that debugger started referring to a failed assertion in DoublyLinkedList.h:512

How can I leave that mode? And why is the keyboard layout there reverted back to a US keyboard layout?

your kernel got panic, but you can try continue (sometimes, it can help)

the help command display all the possible commands

see “Kernel Debugging Land - KDL” section in the page.
http://www.haiku-os.org/docs/welcome/de/bugreports.html

Thank you, I will remember this (I hope so) for to give it a try next time the kernel debugger will hit me.