docs: Clarify phpdoc

src/Libs/Validator.php

@@ -103,9 +103,9 @@ class Validator
      * Builds the human-readable message for a single failed validation.
      *
      * Pure helper: it only reads its arguments and never reads nor writes
-     * $lastFailed or any other state, and it is independent of Request. A
-     * controller may adopt it (opt-in) to render a message with :attribute in
-     * place of Request's default text.
+     * $lastFailed or any other state. Request::validate() uses it to produce
+     * the single error message it sends, forwarding its messages() and
+     * attributes() maps; it can also be called directly by controllers.
      *
      * Resolution order for the message text:
      *   1. $messages[$lastFailed]         override by full "field.rule:args"