feat: improve AI dialogue evaluation and capability boundaries

kouyu_english/lib/features/lesson/steps/independent_step.dart

@@ -99,16 +99,17 @@ class _IndependentStepState extends State<_IndependentStep>
       checkingWithAi = true;
       aiCheckError = null;
     });
-    final feedback = await AiService.instance.answerFeedback(
-      provider: widget.state.aiProvider,
-      endpoint: widget.state.aiEndpoint,
-      model: widget.state.aiModel,
-      answerId: widget.segmentId,
-      target: widget.activity.independentHelp,
-      taskPrompt: widget.activity.independentPrompt,
-      answer: answer,
-      level: lessonLevel(widget.lessonId),
-    );
+    final feedback = await AiService.instance.capabilities.evaluation
+        .evaluateAnswer(
+          provider: widget.state.aiProvider,
+          endpoint: widget.state.aiEndpoint,
+          model: widget.state.aiModel,
+          answerId: widget.segmentId,
+          target: widget.activity.independentHelp,
+          taskPrompt: widget.activity.independentPrompt,
+          answer: answer,
+          level: lessonLevel(widget.lessonId),
+        );
     // The learner may have kept typing while the request ran.
     if (!mounted || widget.controller.text.trim() != answer) {
       if (mounted) setState(() => checkingWithAi = false);