feat(post): add idempotency support for post creation with client request ID

Add client_request_id field to post creation endpoints (CreateVotePost and CreatePostWithSegments).
When provided, the server uses Redis SetNX-based idempotency to prevent duplicate posts
from double-clicks or network retries within a 24-hour TTL. Duplicate requests return
the originally created post; concurrent in-flight requests return 429 "正在发布中，请稍候".

internal/service/vote_service.go

@@ -66,6 +66,23 @@ func (s *voteService) CreateVotePost(ctx context.Context, userID string, req *dt
 		return nil, errors.New("投票选项最多10个")
 	}
 
+	// 幂等检查：同一 userID + clientRequestID 在 TTL 内只创建一次。
+	// 重复请求（多次点击、网络重试）会命中已回填的 postID，直接返回首次创建的帖子。
+	if req.ClientRequestID != "" && s.cache != nil {
+		idemKey := cache.PostCreateIdempotentKey(userID, req.ClientRequestID)
+		result := cache.TryAcquireIdempotency(ctx, s.cache, idemKey, PostCreateIdempotentTTL)
+		if !result.Acquired {
+			// 命中已完成的请求：返回首次创建的帖子。
+			if result.ExistingValue != "" {
+				if existing, err := s.postRepo.GetByID(result.ExistingValue); err == nil && existing != nil {
+					return s.convertToPostResponse(existing, userID), nil
+				}
+			}
+			// 命中"进行中"占位：前一个请求还在处理，拒绝重复提交。
+			return nil, ErrDuplicatePostRequest
+		}
+	}
+
 	// 构建 vote segment
 	voteOptions := make([]dto.VoteOptionData, len(req.VoteOptions))
 	for i, opt := range req.VoteOptions {
@@ -103,9 +120,18 @@ func (s *voteService) CreateVotePost(ctx context.Context, userID string, req *dt
 
 	err := s.postRepo.Create(post, req.Images)
 	if err != nil {
+		// 创建失败：释放幂等占位，允许用户重试。
+		if req.ClientRequestID != "" && s.cache != nil {
+			cache.ReleaseIdempotency(ctx, s.cache, cache.PostCreateIdempotentKey(userID, req.ClientRequestID))
+		}
 		return nil, err
 	}
 
+	// 创建成功：回填幂等键为 postID，使后续重复请求返回同一帖子。
+	if req.ClientRequestID != "" && s.cache != nil {
+		cache.CompleteIdempotency(ctx, s.cache, cache.PostCreateIdempotentKey(userID, req.ClientRequestID), post.ID, PostCreateIdempotentTTL)
+	}
+
 	// 异步审核
 	go s.reviewVotePostAsync(post.ID, userID, req.Title, content, req.Images)