In below image I'd like to move the position of the green anchor point along the green dotted line (I freehanded in there, image it's a straight extension of the anchor point handle's line). I'd like to do so while keeping the cyan anchor point in place as well as the direction of the green line locked. Note that this is not a snapping angle (90, 45, etc) nor do I have any lines I could snap to.
Is this possible somehow?
The only way I can think of is to draw a line the direction of the green line and snap to it, but this seems very backward.