To make Araneida use the Slime debugger, use the following code:

(setf araneida:*restart-on-handler-errors*
  (lambda (foo)
     (swank:swank-debugger-hook foo nil)))


Caveat emptor:
- I've only tested this from the slime-repl. You can set the variable at any time, though.
- I have no idea what will happen if you disconnect slime without resetting it.
- It's generally not very well tested.

Disconnecting Slime doesn't break it, as such; it reverts to debugging on the console.