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
 

review/persona.go

@@ -52,6 +52,9 @@ func LoadPersona(path string) (*Persona, error) {
 	if err != nil {
 		return nil, fmt.Errorf("read persona file %s: %w", path, err)
 	}
+	if !info.Mode().IsRegular() {
+		return nil, fmt.Errorf("persona file %s is not a regular file", path)
+	}
 	if info.Size() > MaxPersonaFileSize {
 		return nil, fmt.Errorf("persona file %s exceeds maximum size (%d bytes)", path, MaxPersonaFileSize)
 	}
@@ -59,6 +62,11 @@ func LoadPersona(path string) (*Persona, error) {
 	if err != nil {
 		return nil, fmt.Errorf("read persona file %s: %w", path, err)
 	}
+	// Re-check size after read to defend against TOCTOU races where file
+	// grows between stat and read (e.g., appending process, replaced file).
+	if len(data) > MaxPersonaFileSize {
+		return nil, fmt.Errorf("persona file %s exceeds maximum size (%d bytes)", path, MaxPersonaFileSize)
+	}
 	return parsePersona(data, path)
 }
 
@@ -144,7 +152,10 @@ func parsePersona(data []byte, source string) (*Persona, error) {
 
 // unmarshalYAMLWithDepthLimit unmarshals YAML data with explicit depth limiting.
 // This protects against stack exhaustion from deeply nested structures.
-func unmarshalYAMLWithDepthLimit(data []byte, out interface{}, maxDepth int) error {
+// Note: Multi-document YAML files are accepted but only the first document is
+// parsed; additional documents are silently ignored. This is acceptable for
+// persona files where multi-document support is not a use case.
+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 {
@@ -159,10 +170,16 @@ func unmarshalYAMLWithDepthLimit(data []byte, out interface{}, maxDepth int) err
 }
 
 // checkYAMLDepth recursively checks that YAML nodes don't exceed the depth limit.
+// Handles alias nodes by following the Alias pointer to check the target's depth.
 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: follow the alias to its anchor target.
+	// The alias itself doesn't add depth, but we must check the target.
+	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