I can not find any way for the DRC to catch minimum clearance between traces of the same net. Is there such a function?
I did send a 6-layer board to my manufacturing house with a design which required length tuned traces. Their software caught a problem as a “same net clearance” < 0.2mm.
This happened after I tuned the length of a track and afterwards edited the track manually. The picture below shows an example of the situation.
This would be very difficult to implement. Necessarily each segment touches the previous and the next segment. The check should allow that, but not others. This might still be reasonable by taking the joints into consideration: the directly joined segment wouldn’t violate. But this would work only for straight segments. KiCad has arc shaped tracks where a segment can go away and then come back closer. V8 even allows attaching a net to an arbitrary shape (although I don’t know how this condition reacts to that – is it a graphical item or a track?).
I once did a heater element with this kind of shape. It’s of course pretty long and takes time to route. I really would have appreciated a realtime constraint which would have forced the angles to be 90 degrees and limited the clearance to certain value.