1. if i made walls from sepeate boxes

now im trying to select 2 polygon of 2 diffrent boxes to bridge

and cant. only will let me from the same box

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2.also when im editing the ploygon and moving the walls it works ok but i cant snap. and when im putting snap on, the extude wont be to the dierection of the wall it will go any dierction/

you can see here snap is off i can extrude fine but cannot snap to the exact corner/

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now snap is on and the extrude is like that