新增：帖子详情页真实数据整页替换——四态/真九宫格大图/评论区/关注双态，Feed 导航与互动全接线，demo 详情退役（T3-15/16）

- post_detail_page 整页重写：内存副本先渲染 + getPost 拉新、四态
 （loading/error+重试/ready/40403 提示后返回 Feed 并刷新）；媒体全量
  ——单图原比例（高度钳制 [0.75w,1.33w]）、多图真九宫格（D11 轮播
  弃用，本单裁定）+ InteractiveViewer 全屏大图（03 号拍板 E）
- 评论区：游标列表触底补页 + 底部输入条创建（幂等键在数据层）+
  仅本人评论渲染删除入口（40301/40404 服务端兜底）；成败埋点对
 （durationMs 取输入会话起点、attemptSeq 会话内递增）；CommentTile
  升共享组件（@ 回复前缀呈现、降级作者「宠友」占位）
- 关注双态钮（tonal ＋关注 / Outlined 已关注 + 取关确认）乐观翻转、
  回滚零动画 + SnackBar，user_followed/unfollowed(post_detail) 挂接；
  本人帖不渲染
- Feed 接通：整卡与评论钮导航详情（T3-14 占位提示移除）、点赞/收藏
  接共享 ToggleSync（详情与卡片同一实例跨页一致）、toggleError
  一次性 SnackBar 消费
- 主壳/装配：openPost 按 postId push；create demo 流不再导航已退役的
  demo 详情（发布页真实化留 T3-17）；AppState 在 post_detail/Feed 面
  消费清零
- compose 冒烟（env 门控默认跳过）：真链路发帖/点赞幂等/收藏/评论/
  删评一轮 + 断网点赞回滚（生产 ApiClient 异常链）

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

test/helpers/community_test_helpers.dart

@@ -76,13 +76,15 @@ Map<String, dynamic> sampleFeedCardJson({
 
 Map<String, dynamic> sampleCommentJson({
   String id = 'c-1',
+  Map<String, dynamic>? author,
   Map<String, dynamic>? replyToUser,
+  String content = '好可爱！',
 }) => {
   'id': id,
   'postId': 'p-1',
-  'author': sampleAuthorJson(),
+  'author': author ?? sampleAuthorJson(),
   'replyToUser': replyToUser,
-  'content': '好可爱！',
+  'content': content,
   'createdAt': '2026-09-08T11:00:00.000Z',
 };
 
@@ -131,6 +133,42 @@ CursorPage<FeedCard> feedPage(
   bool hasMore = false,
 }) => CursorPage(items: items, nextCursor: nextCursor, hasMore: hasMore);
 
+Post samplePost({
+  String id = 'p-1',
+  bool likedByMe = false,
+  int likeCount = 6,
+  bool bookmarkedByMe = false,
+  int bookmarkCount = 2,
+}) => Post.fromJson(
+  samplePostJson(
+    id: id,
+    likedByMe: likedByMe,
+    likeCount: likeCount,
+    bookmarkedByMe: bookmarkedByMe,
+    bookmarkCount: bookmarkCount,
+  ),
+);
+
+PostComment sampleComment({
+  String id = 'c-1',
+  Map<String, dynamic>? author,
+  Map<String, dynamic>? replyToUser,
+  String content = '好可爱！',
+}) => PostComment.fromJson(
+  sampleCommentJson(
+    id: id,
+    author: author,
+    replyToUser: replyToUser,
+    content: content,
+  ),
+);
+
+CursorPage<PostComment> commentPage(
+  List<PostComment> items, {
+  String? nextCursor,
+  bool hasMore = false,
+}) => CursorPage(items: items, nextCursor: nextCursor, hasMore: hasMore);
+
 /// 假仓库：controller 测试注入行为并记录调用（Completer 控时序）。
 /// 未注入 handler 的方法一律 UnimplementedError（误触发即测试失败）。
 class FakeCommunityRepository implements CommunityRepository {
@@ -141,6 +179,13 @@ class FakeCommunityRepository implements CommunityRepository {
   Future<LikeState> Function(String postId, bool target)? onLikeToggle;
   Future<BookmarkState> Function(String postId, bool target)? onBookmarkToggle;
   Future<Post> Function(String postId)? onGetPost;
+  Future<CursorPage<PostComment>> Function(String postId, String? cursor)?
+  onListComments;
+  Future<PostComment> Function(String postId, CreateCommentRequest request)?
+  onCreateComment;
+  Future<void> Function(String commentId)? onDeleteComment;
+  Future<FollowState> Function(String userId, bool target)? onFollowToggle;
+  Future<FollowStats> Function(String userId)? onGetFollowStats;
   Future<MediaUploadCredentials> Function(CreateMediaUploadRequest request)?
   onCreateMediaUpload;
   Future<MediaAsset> Function(String assetId)? onCompleteMediaUpload;
@@ -218,28 +263,45 @@ class FakeCommunityRepository implements CommunityRepository {
     String postId, {
     int? limit,
     String? cursor,
-  }) => throw UnimplementedError();
+  }) {
+    calls.add('comments:$postId:cursor=$cursor');
+    return onListComments!(postId, cursor);
+  }
 
   @override
   Future<PostComment> createComment(
     String postId,
     CreateCommentRequest request,
-  ) => throw UnimplementedError();
+  ) {
+    calls.add('createComment:$postId:${request.content}');
+    return onCreateComment!(postId, request);
+  }
 
   @override
-  Future<void> deleteComment(String commentId) => throw UnimplementedError();
+  Future<void> deleteComment(String commentId) {
+    calls.add('deleteComment:$commentId');
+    return onDeleteComment!(commentId);
+  }
+
+  @override
+  Future<FollowState> followUser(String userId) {
+    calls.add('follow:$userId');
+    return onFollowToggle!(userId, true);
+  }
+
+  @override
+  Future<FollowState> unfollowUser(String userId) {
+    calls.add('unfollow:$userId');
+    return onFollowToggle!(userId, false);
+  }
+
+  @override
+  Future<FollowStats> getFollowStats(String userId) {
+    calls.add('followStats:$userId');
+    return onGetFollowStats!(userId);
+  }
 
   @override
   Future<CursorPage<FeedCard>> listMyBookmarks({int? limit, String? cursor}) =>
       throw UnimplementedError();
-
-  @override
-  Future<FollowState> followUser(String userId) => throw UnimplementedError();
-
-  @override
-  Future<FollowState> unfollowUser(String userId) => throw UnimplementedError();
-
-  @override
-  Future<FollowStats> getFollowStats(String userId) =>
-      throw UnimplementedError();
 }