Often, when building a game or the like out of PSTNs, we wish we could override PSTN's realistic (but annoying) tendency to stop whenever it hits something when trying to retract.
My suggestion is very simple: Make PSTN with a life of 2 override the blocking check on retraction - erasing any particles that get in the way of retraction (except DMND, perhaps).
This would also add a new, reliable method of 'deleting - if - present,' when CRAY(SPRK) is too uneliable and imprecise for the given project, and allow saves heavily reliant on PSTN to get a small speed boost if the bonds check can be skipped.