Invite a multi-national Edencom/CONCORD operation to guard the facility and to share what is learned.
Is that so very unreasonable? More unreasonable that asking me to not be afraid when I see it in the hands of Amarr only?
Also you are entirely correct. I do not need a casus belli. If I wanted a war with LUMEN I could start one tomorrow, and no one would bat an eyelid, including LUMEN. I would not need to justify it in any particular way. Naava Edios would no doubt sigh and roll her eyes and ask us if we must but that would be the worst diplomatic fallout I can imagine.