feat(报告)：AI 聚合残片生成报告草稿

- AiServiceClient：调用 lpt-ai 独立服务，未配置/失败时返回 empty
- GET /study-sessions/{sessionNum}/report-draft：AI 聚合（含预期对比），降级为残片拼接
- 草稿仅作为编辑起点，最终报告仍由用户确认后保存
- application.yml 增加 lpt.ai-service.url 配置

src/main/java/com/guo/learningprogresstracker/service/impl/StudySessionsServiceImpl.java

@@ -16,6 +16,7 @@ import com.guo.learningprogresstracker.mapStruct.StudySessionConvert;
 import com.guo.learningprogresstracker.mapper.StudyReportFragmentsMapper;
 import com.guo.learningprogresstracker.mapper.StudyReportsMapper;
 import com.guo.learningprogresstracker.mapper.StudySessionsMapper;
+import com.guo.learningprogresstracker.service.StudyExpectationsService;
 import com.guo.learningprogresstracker.service.StudySessionsService;
 import lombok.RequiredArgsConstructor;
 import lombok.extern.slf4j.Slf4j;
@@ -41,6 +42,8 @@ public class StudySessionsServiceImpl extends ServiceImpl<StudySessionsMapper, S
     private final StudyReportFragmentsServiceImpl studyReportFragmentsServiceImpl;
     private final StudyReportFragmentsMapper studyReportFragmentsMapper;
     private final StudyReportsMapper studyReportsMapper;
+    private final AiServiceClient aiServiceClient;
+    private final StudyExpectationsService studyExpectationsService;
 
     public StudySessionResponse startOrContinueStudySession(String taskNum) throws NotFindEntitiesException, ServiceException {
         TaskEntity taskEntity = tasksServiceImpl.getOneOpt(
@@ -158,4 +161,30 @@ public class StudySessionsServiceImpl extends ServiceImpl<StudySessionsMapper, S
         return StudySessionConvert.MAPPER.toStudySessionResponse(session);
     }
 
+    /**
+     * 生成学习报告草稿：优先调用 lpt-ai 聚合残片，服务不可用时降级为按序拼接。
+     * 草稿仅作为编辑起点返回，不落库——最终报告由用户确认后经 endedStudySession 保存。
+     */
+    public String generateReportDraft(String sessionNum) throws ErrorParameterException {
+        StudySessionsEntity session = this.getOneOpt(Wrappers.lambdaQuery(StudySessionsEntity.class)
+                        .eq(StudySessionsEntity::getSessionNum, sessionNum))
+                .orElseThrow(() -> new ErrorParameterException("会话[" + sessionNum + "]不存在"));
+
+        ArrayList<String> fragments = getAllFragments(sessionNum);
+        if (fragments.isEmpty()) {
+            return "";
+        }
+
+        String taskName = tasksServiceImpl.getOneOpt(
+                        Wrappers.lambdaQuery(TaskEntity.class).eq(TaskEntity::getTaskNum, session.getTaskNum()))
+                .map(TaskEntity::getTaskName)
+                .orElse("学习任务");
+        String expectation = Optional.ofNullable(studyExpectationsService.getBySessionNum(sessionNum))
+                .map(e -> e.getDescription())
+                .orElse(null);
+
+        return aiServiceClient.aggregateReport(taskName, fragments, expectation)
+                .orElseGet(() -> String.join("\n", fragments));
+    }
+
 }