As you can see every context links only to nodes that already exist in
the graph.  In the graph-cons example you see that node A cannot have
any links to other nodes, because none exist.  The edges between A and C
and A and B are added later when the contexts of these nodes are cons’d
onto the graph.  That’s the big idea behind inductive graphs.

To make the graphviz bindings work you need to set GUILE_EXTENSIONS_PATH
first.  I recommend this:

$ guix shell graphviz guile
$ [env] export GUILE_EXTENSIONS_PATH=$GUIX_ENVIRONMENT/lib/guile/3.0/extensions
$ [env] guile --listen

Then M-x connect-to-guile in a graphical Emacs and evaluate the code
above to see the graph visualization.

Hope this helps!

-- 
Ricardo