Offset curve on surface, sharp?

Hello,
This might be a silly question…
I often have to offset curves on surfaces when modelling however, there doesn’t seem to be the same corner options (Sharp/Round/Smooth/Chamfer/None) present when offsetting a curve that’s not on a surface…
Currently i work around this by exploding the offset curve on the surface, then manually extending, trimming and joining but, Its quite laborious… Is there a way to get the curve on surface to offset both sides and create caps? it would save me a lot of time…
Have I missed something obvious, is there a faster way to do this?

(bonus question… why is that sometimes when I do a Loose=Yes surface offset, then offset the new surfaces border as a curve on it, it explodes into dozens of new curves but, if I do the same but use Loose=No, then offset that new surface’s edge as a curve on its surface it works?)