Droid-2 stuck at boot
Not a satisfying answer: nothing tried lead to success, so I ended up performing a factory-reset after having removed the replaced system app. It isn't sure that app caused the issue, but that was the only change to the system itself applied shortly before – so better play it safe.

That brought the device "back to live" (checked for several weeks to make sure – before updating to the latest CM available for it, which brought it up to 4.4.4 Kitkat).