This is probably not actually correct, but if you change
self.attributeAffects(self.aaaAttr, self.inMeshAttr)
self.attributeAffects(self.inMeshAttr, self.tttAttr)
to just
self.attributeAffects(self.aaaAttr, self.tttAttr)
it does start triggering the compute for me. Doesn't make a lot of sense why though...