This commit IS relevant for touching the edge of spike plane sectors! You can force the touching-the-edge-of-sector-activates-effect function for spike planes instead of relying on a thinker, but until that's done, this WILL make it possible to teeter on the edge of thorn surfaces in CEZ.

Of course there'd been something like this. After mulling it over for a bit, I've decided to go with the simplest fix: If a sector has spike damage, SF_TRIGGERSPECIAL_TOUCH is turned on automatically. I'm aware that this also affects other sector specials that may be applied to the same sector, but even if there are any maps out there that combine spike damage with another sector special, I can't imagine that they rely on the fact that spike damage is triggered on touch while the other effect isn't. The alternative would be adding a special case for spike damage to every place that checks for SF_TRIGGERSPECIAL_TOUCH, and that would just make everything messier.

I have an alternate thought for thinking beyond basic map compatibility. What if SF_TRIGGERSPECIAL_TOUCH was the default behaviour in UDMF maps, and the sector flag application method allowed for an occasionally specific disabling of this? The number of times I've seen new players try to push the Egg Capsule buttons down by standing on their edge and wondering why it's not working is a big indicator this is a problem, to the point that I intentionally gave the CEZ3 buttons SF_TRIGGERSPECIAL_TOUCH to prevent that from happening in the heat of the fight.

I agree, and in fact I'm planning to do exactly that in the UDMF branch. Which means that the special handling for SF_TRIGGERSPECIAL_TOUCH on spikes will eventually shuffle off into the binary-to-UDMF conversion function and be left to rot there.