and it immediately got downvoted. The problem is something I will encounter many times in a competitive work environment. I want to improve this question to make sure it doesn't get closed and gets a useful answer. Any suggestions?
Cut out all the superfluous detail, change the title to something like...
"How can I negotiate with management when a coworker is poisoning the well."
Right now, it seems a bit rant-ish and too bogged down with detail which makes your goal a bit less than clear.
Something more like
My company has two divisions, that both use a common technology. A coworker had been setting himself up as the lead of that technology for both divisions.
I was specifically hired by my division to create an independent function for this technology. My division wants control of this tech, but also wants to maintain good relations with the other division
A coworker from the other division demanded full access to my work, and after some push back, management from both divisions is setting up a meeting to discuss collaboration.
I want this meeting to go in such a way that I neither look weak, nor do I want to make my coworker lose face, or depart from my divisions goal of greater independence. Having him involved would undermine such independence.
On paper it would be very easy to say "we are two divisions, but of course we are going to be collaborating on specific projects, and if you need my help in A I am happy to advise", using the legitimate organisational structure to push back.
Question: How can I push back against the demand for full access to my work (projects and customers) while maintaining good relationships with the other division?