feat(settings): 后台可配置 Markdown 代码块自动折叠与阈值行数

支持开关与 0–100 行阈值（0 为无预览），经站点设置与 WS 热更新；短代码在视口内收起时不再回滚浏览位置。

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/service/setting.go

@@ -20,16 +20,23 @@ const (
 	SettingKeySiteName             = "site_name"
 	SettingKeySiteDescription      = "site_description"
 	SettingKeyAllowRegister        = "allow_register"
-	SettingKeyPostCooldownHours    = "post_cooldown_hours"
+	SettingKeyPostCooldownHours = "post_cooldown_hours"
+	// SettingKeyCodeBlockAutoFold 代码块自动折叠；缺行视为开启
+	SettingKeyCodeBlockAutoFold = "code_block_auto_fold"
+	// SettingKeyCodeBlockFoldLines 超过该行数则折叠；0=无预览；缺行=5
+	SettingKeyCodeBlockFoldLines = "code_block_fold_lines"
 )
 
 const (
 	DefaultSiteName        = "姜十三论坛"
 	DefaultSiteDescription = "姜十三论坛 - 技术分享与讨论社区"
 	DefaultCooldownHours   = 24
+	DefaultCodeFoldLines   = 5
 	MaxSiteNameRunes       = 32
 	MaxSiteDescRunes       = 160
 	MaxCooldownHours       = 168
+	MinCodeFoldLines       = 0
+	MaxCodeFoldLines       = 100
 )
 
 // ErrInvalidAccent 主题色格式非法
@@ -48,6 +55,8 @@ type PublicSiteSettings struct {
 	SiteDescription       string `json:"site_description"`
 	AllowRegister         bool   `json:"allow_register"`
 	PostCooldownHours     int    `json:"post_cooldown_hours"`
+	CodeBlockAutoFold     bool   `json:"code_block_auto_fold"`
+	CodeBlockFoldLines    int    `json:"code_block_fold_lines"`
 }
 
 // SettingService 站点级键值设置
@@ -108,6 +117,8 @@ func (s *SettingService) Public() (PublicSiteSettings, error) {
 		TrustReviewedPublish: true,
 		AllowRegister:        true,
 		PostCooldownHours:    DefaultCooldownHours,
+		CodeBlockAutoFold:    true,
+		CodeBlockFoldLines:   DefaultCodeFoldLines,
 	}
 	accent, err := s.AccentColor()
 	if err != nil {
@@ -151,6 +162,18 @@ func (s *SettingService) Public() (PublicSiteSettings, error) {
 		return out, err
 	}
 	out.PostCooldownHours = hours
+
+	fold, err := s.CodeBlockAutoFold()
+	if err != nil {
+		return out, err
+	}
+	out.CodeBlockAutoFold = fold
+
+	foldLines, err := s.CodeBlockFoldLines()
+	if err != nil {
+		return out, err
+	}
+	out.CodeBlockFoldLines = foldLines
 	return out, nil
 }
 
@@ -223,6 +246,7 @@ func (s *SettingService) SetAllowRegister(on bool) error {
 	return s.setBoolDefaultTrue(SettingKeyAllowRegister, on)
 }
 
+
 // PostCooldownHours 新用户发帖冷静期（小时）。缺行=24；0 表示关闭。
 func (s *SettingService) PostCooldownHours() (int, error) {
 	v, found, err := s.getValue(SettingKeyPostCooldownHours)
@@ -251,3 +275,46 @@ func (s *SettingService) SetPostCooldownHours(hours int) error {
 	}
 	return s.putValue(SettingKeyPostCooldownHours, strconv.Itoa(hours))
 }
+
+// CodeBlockAutoFold 是否对超过阈值行数的 Markdown 代码块默认折叠。缺行视为开启。
+func (s *SettingService) CodeBlockAutoFold() (bool, error) {
+	v, found, err := s.getValue(SettingKeyCodeBlockAutoFold)
+	if err != nil {
+		return true, err
+	}
+	return parseBoolDefaultTrue(v, found), nil
+}
+
+// SetCodeBlockAutoFold 持久化代码折叠开关；开启时删键保持「缺行=默认开」。
+func (s *SettingService) SetCodeBlockAutoFold(on bool) error {
+	return s.setBoolDefaultTrue(SettingKeyCodeBlockAutoFold, on)
+}
+
+// CodeBlockFoldLines 超过该行数则折叠（折叠预览约同高；0=无预览）。缺行=5。
+func (s *SettingService) CodeBlockFoldLines() (int, error) {
+	v, found, err := s.getValue(SettingKeyCodeBlockFoldLines)
+	if err != nil {
+		return DefaultCodeFoldLines, err
+	}
+	if !found {
+		return DefaultCodeFoldLines, nil
+	}
+	n, convErr := strconv.Atoi(strings.TrimSpace(v))
+	if convErr != nil || n < MinCodeFoldLines {
+		return DefaultCodeFoldLines, nil
+	}
+	if n > MaxCodeFoldLines {
+		return MaxCodeFoldLines, nil
+	}
+	return n, nil
+}
+
+func (s *SettingService) SetCodeBlockFoldLines(lines int) error {
+	if lines < MinCodeFoldLines || lines > MaxCodeFoldLines {
+		return ErrInvalidSiteSetting
+	}
+	if lines == DefaultCodeFoldLines {
+		return s.deleteKey(SettingKeyCodeBlockFoldLines)
+	}
+	return s.putValue(SettingKeyCodeBlockFoldLines, strconv.Itoa(lines))
+}