Clarify prompt input requirement documentation

types.go

@@ -344,7 +344,9 @@ type ProfileInspection struct {
 type PromptInputDefinition struct {
 	// Name is the normalized prompt input name.
 	Name string
-	// Required reports whether preparation requires the input.
+	// Required is the prompt definition's declared required flag. When true,
+	// preparation fails if the input is omitted. A false value does not account
+	// for input references in message or session-ID templates.
 	Required bool
 	// ContentType is the declared input media-type metadata.
 	ContentType string