Extrude is currently limited to linear extrusions, as far as I can tell, and lathe, even with the helical mode in development, can only extrude around an arbitrary normal (helical mode just allows for interruption and translation, as I understand it). When dealing with a part whose profile has an arbitrary number of curves and a lip, the only way I can find to create the part is to do a linear extrude of the arbitrary shape and subtract an inner extrusion. This is a fairly standard mode of design, but it poses a problem when that lip needs a radius. As there is no way to extrude a profile along an arbitrary path, one can't simply design the profile of the lip and then extrude it along the orignal profile curve for the base linear extrusion (which is a common route to take in some CAD software), and since there aren't any 3D tools, it's not possible to simply apply a tool to the faces to create the edge profile needed (this is another route commonly taken by CAD software).

Right now, the primary things standing in the way of SolveSpace being my primary go-to package (and possibly even avoid paying for future upgrades to my commercial packages fingers crossed) are the lack of edge tools and the inability to do any kind of skin, patch, loft, or hull operations (while not interchangeable, one or two of them can usually be used to solve for the absence of the others).