Name pathWalk's modes, and draw a path only through drawPath once it is proved

graph.go

@@ -165,10 +165,7 @@ func renderEdges(n node) []renderEdge {
 // already proved the tail resolves in every variant.
 func pathLeaves(n node, tail []string) []node {
 	var out []node
-	_, _ = walkPath(n, tail, pathWalk{
-		choice: func(c *choice, _ []string) ([]node, error) { return c.items, nil },
-		leaf:   func(n node) error { out = append(out, n); return nil },
-	})
+	_, _ = walkPath(n, tail, pathWalk{mode: walkEvery, pins: &pinSet{}, leaf: func(n node) error { out = append(out, n); return nil }})
 	return out
 }