This draft is over 100 days old.

IMHO (topological-sort graph [=]) is OK as is.

Is the spec written correctly?

"Each connection is a list of the form (node dependency dependency ...),
meaning that dependencies are dependent on node." -> Is this the
customary order to write the graph? Makefile and similar syntaxes uses
(node dependency dependency ...) where node is dependent on that
dependencies. I'd anticipate this is more convenient for most
applications. A utility to invert the graph would be needed.

"It is an error if the same node (in the sense of =) appears in more
than one connection." -> Appears at the head of more than one connection?

Another procedure that returns each
https://en.wikipedia.org/wiki/Strongly_connected_component as a list
should probably be added.