feat: improve AI dialogue evaluation and capability boundaries

kouyu_english/lib/core/models.dart

@@ -26,6 +26,58 @@ enum EvidenceKind {
   pending,
 }
 
+/// Local dialogue matching is intentionally tri-state. A natural English
+/// reply that does not match a strict taught-language rule is unknown, not
+/// automatically wrong.
+enum LocalDialogueVerdict { accepted, rejected, uncertain }
+
+enum DialogueAiVerdict { accepted, correctable, offTopic, uncertain }
+
+enum DialogueValidationSource {
+  local,
+  ai,
+  localAndAi,
+  disagreement,
+  unavailable,
+}
+
+enum DialogueSupportLevel {
+  none,
+  validationOnly,
+  hint,
+  translation,
+  correction,
+  skipped,
+}
+
+/// The application-owned result of combining local rules with advisory AI.
+/// Conversation progress and mastery evidence are deliberately separate.
+class DialogueTurnDecision {
+  const DialogueTurnDecision({
+    required this.canAdvance,
+    required this.evidenceOutcome,
+    required this.validationSource,
+    required this.supportLevel,
+    this.feedback,
+    this.suggestion,
+  });
+
+  final bool canAdvance;
+  final EvidenceKind evidenceOutcome;
+  final DialogueValidationSource validationSource;
+  final DialogueSupportLevel supportLevel;
+  final String? feedback;
+  final String? suggestion;
+
+  bool get assisted => switch (supportLevel) {
+    DialogueSupportLevel.hint ||
+    DialogueSupportLevel.translation ||
+    DialogueSupportLevel.correction ||
+    DialogueSupportLevel.skipped => true,
+    _ => false,
+  };
+}
+
 class AttemptEvidence {
   const AttemptEvidence({
     required this.id,
@@ -117,7 +169,12 @@ class DialogueAiIntervention {
     required this.accepted,
     this.suggestion,
     required this.explanation,
-  });
+    this.schemaVersion = 'dialogue-intervention-1',
+    this.turnId,
+    this.verdict = DialogueAiVerdict.uncertain,
+    bool? goalSatisfied,
+    this.reasonCode = 'unspecified',
+  }) : goalSatisfied = goalSatisfied ?? accepted;
 
   /// Whether the learner's response is semantically acceptable for the turn.
   final bool accepted;
@@ -127,6 +184,11 @@ class DialogueAiIntervention {
 
   /// Encouraging, concise Chinese explanation of the situation and recommendation.
   final String explanation;
+  final String schemaVersion;
+  final String? turnId;
+  final DialogueAiVerdict verdict;
+  final bool goalSatisfied;
+  final String reasonCode;
 }
 
 class AssessmentRecord {
@@ -169,11 +231,17 @@ class DialogueDraft {
     required this.stage,
     required this.turns,
     required this.usedHelp,
+    this.currentTurnHintUsed = false,
+    this.currentTurnTranslationUsed = false,
+    this.currentTurnCorrectionUsed = false,
   });
   final String lessonId;
   final int stage;
   final List<DialogueTurn> turns;
   final bool usedHelp;
+  final bool currentTurnHintUsed;
+  final bool currentTurnTranslationUsed;
+  final bool currentTurnCorrectionUsed;
 }
 
 class LessonSummary {