fix(decode): terminate the schema walk on a self-embedded pointer struct

Assisted-by: GLM 5.3

decode.go

@@ -255,8 +255,15 @@ type structSchema struct {
 
 func newStructSchema(t reflect.Type) structSchema {
 	s := structSchema{byName: make(map[string]structFieldLoc, t.NumField())}
+	// A struct may embed a pointer to itself, which is legal Go, so the walk
+	// tracks the struct types on the current path and stops when one repeats;
+	// without the guard the recursion never terminates. A self-promoted key
+	// always loses to the shallower original, so skipping it changes nothing.
+	visiting := map[reflect.Type]bool{}
 	var walk func(t reflect.Type, prefix []int, depth int)
 	walk = func(t reflect.Type, prefix []int, depth int) {
+		visiting[t] = true
+		defer delete(visiting, t)
 		for i := range t.NumField() {
 			f := t.Field(i)
 			if f.PkgPath != "" { // unexported
@@ -277,7 +284,9 @@ func newStructSchema(t reflect.Type) structSchema {
 				}
 				switch {
 				case ft.Kind() == reflect.Struct && !isScalarStruct(ft):
-					walk(ft, path, depth+1)
+					if !visiting[ft] {
+						walk(ft, path, depth+1)
+					}
 					continue
 				case ft.Kind() == reflect.Map && ft.Key().Kind() == reflect.String:
 					s.embedMaps = append(s.embedMaps, path)