I agree with your analysis but I could see two scenarios where this could play out. Neither is likely or logical but they are on brand for Putin.

1) little green men on an adventure. Putin claims to lose control of Wagner and even calls their occupation of the gap outrageous and he/Belarus will fix it with peacekeepers))

2) the people of the gap "demand" to join Kaliningrad or Belarus. A little Donbas mk2 with some conveniently found Russian Poles (they exist) or ring ins from the Rodina. It is ridiculous, of course. But the whole point of it is to stall to create a few facts on the ground. Wagner then is on a humanitarian mission blah blah. When Poland fights back, Russia will have the cameras ready saying how westerners deal with dissent and freedom to choose. Western leaders won't believe it for a second but they aren't the audience. And the Russians in the know will like it for sticking it to the west. Plus, Putin may truly believe the West( and some chance he is right) is to gutless to trigger article 5. The point isn't always to hold that ground but show they can stir up Europe any time they want. Plus a domestic distraction. If it succeeds it is Russia, if it fails it is Wagner.