Finally I fixed all navmesh generation errors and can go continue with the rest of features.

(Navmesh is drawn in green lines).

Now I need to add area tagging and connections, i.e. I move to tile cache now.
After that I need to restructure code a bit so that navmesh build code goes to navmesh class, so to be able to run independently of node tree.

The code is in navigation branch, have fun.