[REFACTOR] 영어 교정 한국어

src/main/java/com/example/todayEng/domain/diary/client/AnswerCorrectionLanguageValidator.java

@@ -0,0 +1,26 @@
+package com.example.todayEng.domain.diary.client;
+
+import java.util.List;
+import java.util.regex.Pattern;
+import org.springframework.stereotype.Component;
+
+@Component
+public class AnswerCorrectionLanguageValidator {
+
+    private static final Pattern HANGUL = Pattern.compile("[가-힣ㄱ-ㅎㅏ-ㅣ]");
+    private static final Pattern LATIN = Pattern.compile("[A-Za-z]");
+
+    public boolean isKoreanExplanation(String value) {
+        return value != null && HANGUL.matcher(value).find();
+    }
+
+    public boolean isEnglishText(String value) {
+        return value != null
+                && LATIN.matcher(value).find()
+                && !HANGUL.matcher(value).find();
+    }
+
+    public boolean areEnglishExpressions(List<String> values) {
+        return values != null && values.stream().allMatch(this::isEnglishText);
+    }
+}

src/main/java/com/example/todayEng/domain/diary/client/GeminiAnswerCorrectionLlmClient.java

@@ -30,13 +30,16 @@ public class GeminiAnswerCorrectionLlmClient implements AnswerCorrectionLlmClien
     private final GeminiProperties properties;
     private final AnswerCorrectionPromptFactory promptFactory;
     private final ObjectMapper objectMapper;
+    private final AnswerCorrectionLanguageValidator languageValidator;
 
     public GeminiAnswerCorrectionLlmClient(@Qualifier("geminiRestClient") RestClient restClient,
-            GeminiProperties properties, AnswerCorrectionPromptFactory promptFactory, ObjectMapper objectMapper) {
+            GeminiProperties properties, AnswerCorrectionPromptFactory promptFactory, ObjectMapper objectMapper,
+            AnswerCorrectionLanguageValidator languageValidator) {
         this.restClient = restClient;
         this.properties = properties;
         this.promptFactory = promptFactory;
         this.objectMapper = objectMapper;
+        this.languageValidator = languageValidator;
     }
 
     @Override
@@ -111,7 +114,10 @@ private String extract(GeminiResponse response) {
     }
 
     private void validate(QuestionType type, AnswerCorrectionLlmResponse r) {
-        if (r == null || blank(r.correctedText()) || blank(r.correctionReason()) || r.alternativeExpressions() == null
+        if (r == null
+                || !languageValidator.isEnglishText(r.correctedText())
+                || !languageValidator.isKoreanExplanation(r.correctionReason())
+                || !languageValidator.areEnglishExpressions(r.alternativeExpressions())
                 || (type == QuestionType.MAIN && (r.followUpQuestion() == null
                 || blank(r.followUpQuestion().questionText()) || blank(r.followUpQuestion().koreanTranslation())))
                 || (type == QuestionType.FOLLOW_UP && r.followUpQuestion() != null)) {

src/main/java/com/example/todayEng/domain/diary/prompt/AnswerCorrectionPromptFactory.java

@@ -13,7 +13,9 @@ public String create(AnswerCorrectionCommand c) {
         return """
                 You are an English reflection-writing coach.
                 Correct the answer at the user's English level while preserving its original meaning.
-                Never invent or add facts. Give a concise correction reason and useful alternative expressions.
+                Never invent or add facts.
+                Write correctionReason only in Korean.
+                Keep correctedText and alternativeExpressions in English.
                 %s
                 English level: %s
                 Question: %s

src/test/java/com/example/todayEng/domain/diary/client/AnswerCorrectionLanguageValidatorTest.java

@@ -0,0 +1,27 @@
+package com.example.todayEng.domain.diary.client;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.util.List;
+import org.junit.jupiter.api.Test;
+
+class AnswerCorrectionLanguageValidatorTest {
+
+    private final AnswerCorrectionLanguageValidator validator = new AnswerCorrectionLanguageValidator();
+
+    @Test
+    void acceptsExpectedLanguages() {
+        assertThat(validator.isEnglishText("It was a good day.")).isTrue();
+        assertThat(validator.isKoreanExplanation("과거형에 맞게 표현을 수정했어요.")).isTrue();
+        assertThat(validator.areEnglishExpressions(List.of("I had a good day.", "It was enjoyable."))).isTrue();
+        assertThat(validator.areEnglishExpressions(List.of())).isTrue();
+    }
+
+    @Test
+    void rejectsLanguageContractViolations() {
+        assertThat(validator.isEnglishText("좋은 하루였어요.")).isFalse();
+        assertThat(validator.isEnglishText("It was 좋은 day.")).isFalse();
+        assertThat(validator.isKoreanExplanation("Changed the sentence to past tense.")).isFalse();
+        assertThat(validator.areEnglishExpressions(List.of("I had fun.", "즐거웠어요."))).isFalse();
+    }
+}

src/test/java/com/example/todayEng/domain/diary/prompt/AnswerCorrectionPromptFactoryTest.java

@@ -17,6 +17,8 @@ void mainPromptRequiresGroundedFollowUpAndMeaningPreservation() throws Exception
                 "It good", EnglishLevel.BEGINNER,
                 new ObjectMapper().readTree("{\"event\":\"walk\"}")));
         assertThat(prompt).contains("preserving its original meaning", "Never invent or add facts",
+                "Write correctionReason only in Korean",
+                "Keep correctedText and alternativeExpressions in English",
                 "exactly one natural follow-up", "BEGINNER", "walk");
     }