Split walkPath's four modes into walkers of their own, sharing how a path steps

render.go

@@ -44,11 +44,10 @@ func (f *Generator) Fake(path string) (string, error) {
 // every call.
 func descend(s *session, root node, segments []string, sc renderScope) (node, error) {
 	// Walked once without drawing first, so a path that fails moves no seeded stream.
-	var probe pinSet
-	if _, err := walkPath(root, segments, pathWalk{mode: walkProbe, pins: &probe}); err != nil {
+	if _, err := (&probeWalk{}).walk(root, segments); err != nil {
 		return nil, err
 	}
-	return drawPath(root, segments, "", &sc.hold().pins, &pathDraws{s: s}), nil
+	return drawPath(root, segments, "", &renderWalk{s: s, pins: &sc.hold().pins}), nil
 }
 
 // render evaluates a compiled node to a string. compile validates every node up