One solution is that actually, the quantum suicide experiment provides evidence for MW, but only to the experimenter. That's really strange. If anything, it seems like that violates Aumann's agreement theorem.

This is the correct solution, but it doesn't violate Aumann's agreement theorem because you and your friend don't have access to the same set of evidence. In particular, you observe yourself surviving exactly in the case that there exists a world in which you survive (properly speaking, the universe doesn't branch in many-worlds, and there aren't actually many worlds, but this doesn't really matter here). Your friend, however, observes you surviving only if both, a: you survive in some world, and b: it's this one. So you get a nice big factor of P(survival somewhere|Many Worlds) = 1 in your update, whereas your friend gets P(survival here|Many Worlds) << 1.