fix: address MINOR review findings from c3e8f0f review

docs/DESIGN-57-yaml-persona.md

@@ -34,21 +34,36 @@ func parsePersona(data []byte, source string) (*Persona, error) {
 ### YAML Parsing with Depth Protection
 
 ```go
-func parseYAML(data []byte, source string) (*Persona, error) {
-    var p Persona
-    // gopkg.in/yaml.v3 does NOT have built-in depth limiting.
-    // Use explicit depth check via yaml.Node API.
-    if err := yaml.Unmarshal(data, &p); err != nil {
-        return nil, fmt.Errorf("parse persona %s: %w", source, err)
+func unmarshalYAMLWithDepthLimit(data []byte, out any, maxDepth int) error {
+    var node yaml.Node
+    dec := yaml.NewDecoder(bytes.NewReader(data))
+    if err := dec.Decode(&node); err != nil {
+        return err
     }
-    if err := validatePersona(&p, source); err != nil {
-        return nil, err
+    if err := checkYAMLDepth(&node, 0, maxDepth); err != nil {
+        return err
     }
-    return &p, nil
+    return node.Decode(out)
+}
+
+func checkYAMLDepth(node *yaml.Node, depth, maxDepth int) error {
+    if depth > maxDepth {
+        return fmt.Errorf("YAML nesting depth exceeds maximum (%d)", maxDepth)
+    }
+    // Handle alias nodes by following the Alias pointer
+    if node.Kind == yaml.AliasNode && node.Alias != nil {
+        return checkYAMLDepth(node.Alias, depth, maxDepth)
+    }
+    for _, child := range node.Content {
+        if err := checkYAMLDepth(child, depth+1, maxDepth); err != nil {
+            return err
+        }
+    }
+    return nil
 }
 ```
 
-The `gopkg.in/yaml.v3` library does not have built-in depth protection, so we implement explicit depth checking by first decoding into a `yaml.Node`, walking the tree to verify depth, then decoding into the target struct.
+The `gopkg.in/yaml.v3` library does not have built-in depth protection, so we implement explicit depth checking by first decoding into a `yaml.Node`, walking the tree to verify depth (including alias resolution), then decoding into the target struct.
 
 ## State/Data Model