Sommers you are not accounting for the unique geography in this game. The only way I can see RB pink-dotting us by beating us to stone/wine location and settling on this side of the oasis.
Pink-dotting as you know, is settling provocatively in the opponents direction, passing by open land to get a city closer to your opponent. Pink-dotting is hostile and provocative. 2metra has already said that he responds to being Pink-dotted by attacking right after the NAP. Why would you expect RB to respond differently?
And more importantly, This is what you are missing. If you can see that them settling the stone is "pink-dotting" us, why can't you see that US settling the stone is pink-dotting them? You don't pink-dot an ally
Finally, If that is the ONLY way you can see them "pink-dotting" us is by claiming the stone, then you are missing something.

I can think of some ways they could get revenge on us and pink-dot us back.
This is key strategic terrain not just for the resources but because it is a wide isthmus linking our respective spheres of influence.
Yes, and we are perfectly within our rights to "claim" it because we saw it first. But the correct way to claim it is to say "Hey we saw this spot first and we want to claim it, but we acknowledge that you might feel provoked by that. That is why we are telling you ahead of time so that if you have objections we can resolve them. We say this to you because we value you as friends and want an open an honest relationship between us."
Once we grab this spot we are good.
No, once we grab this spot (without any notice or conversation with RB) it is the TKY situation all over again, with permanent tension between us and RB for the rest of the game. Or even worse it is a ancient times War as soon as the NAP expires
We could reveal all the info in the world to RB, enter into an alliance of perpetual peace and friendship or even agree to become their vassal and they would still race to claim this key terrain before us.
Melodramatic exagerrations aside, you are wrong about this. If we negotiate to claim this spot with RB's acceptance and approval, there is no race. I dont want to race because it wastes time and resources, especially if you lose.
Right now we have the advantage. There is a good chance that they are not aware of this isthmus. So we can claim it first and control a choke point between our two teams. This would not harm our diplo with them at all as it would be a city clearly in our sphere of influence. It would also block any attempts by RB to settle cities deep in our territory.
We can accomplish all of that by just talking to them. And the so-called advantage we have depends heavily on RB not sending a unit out and discovering the ithsmus on their own, BEFORE we can even settle the spot.
Hell, they might even know about it already. Maybe their first warrior was killed investigating the ithsmus. Has anyone even considered that? EDIT: x posted with a bunch of guys. I see that Caledorn actually mentioned this before me
Sending them a message effectively saying, "Hey guys great to meet you, we urgently want to lock in our boundary with you right away" is only going to telegraph that there is juicy land that we want to get before they get it! So they will immediately focus their scouting in our direction while stalling for time on any deal until they can get a city planted first.
I guarantee you that they are prioritizing finding us already. Given their egos, as 2metra already said, it is unbearable to them that we know where they are and they don't know where we are.
In fact THE BEST way to discourage them from scouting heavily in our direction trying to locate us is to just TELL THEM where we are. By telling them where we are, they will probably put off exploring for us because there is no need and they can use their time exploring in other directions. In this way, being open and honest might actually prevent them from discovering the ithsmus before we can settle it.
EDIT: I don't have any specific use for the stone in mind right now but it's always good to deny a strategic resource to a rival.
No, No, No. It is not "always good" to do that. Denying resources is what starts conflicts. Gosh cav, have you forgotten the Or Here/ereh Ro/Pulsar Plateau conflict already? That BS (CDZ denying Q copper) almost broke up the alliance!
We should only deny a resource is if there is a REASON to do so. The fact that you say you have no use for stone is another reason NOT to provoke hostility over it.
Again, I have no problem with claiming the ithsmus. However, I strongly prefer that we talk to RB about it in advance.