At least for the latter crash-type, I was able to pin-point the culprit: it was the black-light control. Whenever KDE dimmed the panel there was a solid chance the system would reboot—no kernel panic, no stopping. Not even kdump would break its fall. Sure enough, disabling dimming would cure that.
Display dimming can be disabled in KDE's «Engery Saving Settings» |
Now I am waiting for the next crash during reboot before blacklisting the «apple_bl» kernel driver. But maybe the Linux kernel 3.4 that ships with Fedora 17 has mended this issue already. Lets wait and see.