I just bought this used frame at a vintage swap. When I took it home I noticed this little crack on the down tube. I tested it with compress air and soapy water, it is definitely a crack. If I ride this frame, will it break catastrophically? It is a Klein Q Pro carbon team frame from 02-03, aluminum with carbon seat stays. Thanks

Forgot to ask, what options do I have to repair this frame?

Aluminum, correct? You have no economic options.

Most cracks get larger

Once aluminum starts to fail it does not stop.
https://en.wikipedia.org/wiki/Fatigue_limit
And if the frame has reached its limit in one area it could be ready to crack in others.

Think of the frame more as art than a bicycle.
It will look very good hanging on the wall.

If you could afford to weld, heat treat, and paint that would fix the problem. But that's going to cost much more than this frame is worth.