Acoustic Guitar Construction

I tried to be careful removing a bridge with heat, but then this appeared. It goes all the way through.
Pressing on it from the outside and pushing from the inside does not close it, nor does judicious squeezing it together.
Any ideas for an invisible fix?

I have not run in to that, but I am willing to speculate. I wonder if the joint was under stress with the plates dryer than when they were glued up. The stress from very slight shrinkage could pull the joint apart when the glue softened from heat. I am suggesting that because you mention they do not fit back together. I wondering if you put the guitar in a more humid environment. Like cover with plastic with a wet sponge covered as well. Basically treating it as a crack.

It is a do no harm try. (as long as the sponge is not touching the guitar)

My other thought is it was joined as a sprung joint. Then you may need to splint.

Good ideas. Sponge first. Will report.