Have a hall where there is unevenness under carpet down part of the length.
There will be new carpet going down eventually. Found that the subfloor has
a joint that is not on a joist. About an inch away. T&G but it's obviously
been ignored many years. Tongue is broken in some areas.

I plan to put some 2x' from underneath with the face across the joint and
screw the subfloor to it from the top to get the two sides even (I hope).
Then support that 2x with a 2x that is sistered to that nearby joist.
Hoping I can get it pretty even but being in such a conspicuous place, I
think ideally a piece of say luan should go over the floor before the pad
and carpet go down.

This would be fine except that the hallway runs open into the LR area.
Wherever that luan ends a new unevenness is gonna be created I believe.

Maybe I am overthinking this and once I fasten both sides of the joint
solid, the pad and carpet will consume any slight offset.

Opinions and/or ideas?