TOC分页：解决内容超长导致MEDIA_CAPTION_TOO_LONG错误

当目录条目增多超过Telegram caption字符限制时，自动按字符上限分页渲染，
附带翻页inline keyboard（⏮首页/⬅️上一页/➡️下一页），支持photo和text两种模式。

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/toc/renderer.go

@@ -3,53 +3,138 @@ package toc
 import (
 	"fmt"
 	"html"
+	"regexp"
 	"strings"
+	"unicode/utf8"
 )
 
-func (m *Manager) Render() (string, error) {
+var htmlTagRegexp = regexp.MustCompile(`<[^>]*>`)
+
+// htmlTextLength 计算剥离 HTML 标签后的字符数，匹配 Telegram 的计数方式
+func htmlTextLength(s string) int {
+	stripped := htmlTagRegexp.ReplaceAllString(s, "")
+	return utf8.RuneCountInString(stripped)
+}
+
+// renderLines 将所有分类和条目渲染为独立的行
+func (m *Manager) renderLines() (header string, lines []string, footer string, err error) {
 	categories, err := m.storage.ListCategories()
 	if err != nil {
-		return "", err
+		return "", nil, "", err
 	}
 
 	entriesByCategory, err := m.storage.GetEntriesByCategory()
 	if err != nil {
-		return "", err
+		return "", nil, "", err
 	}
 
-	var sb strings.Builder
-	sb.WriteString("📚 <b>频道目录</b>\n")
-	sb.WriteString("━━━━━━━━━━━━━━━\n\n")
+	header = "📚 <b>频道目录</b>\n━━━━━━━━━━━━━━━\n\n"
+	footer = "━━━━━━━━━━━━━━━\n"
 
 	if len(categories) == 0 {
-		sb.WriteString("<i>暂无分类</i>")
-		return sb.String(), nil
+		lines = append(lines, "<i>暂无分类</i>\n")
+		return header, lines, footer, nil
 	}
 
 	for _, cat := range categories {
 		entries := entriesByCategory[cat.Name]
 
-		sb.WriteString(fmt.Sprintf("📁 <b>%s</b>", html.EscapeString(cat.Name)))
+		catLine := fmt.Sprintf("📁 <b>%s</b>", html.EscapeString(cat.Name))
 		if len(entries) > 0 {
-			sb.WriteString(fmt.Sprintf(" (%d)", len(entries)))
+			catLine += fmt.Sprintf(" (%d)", len(entries))
 		}
-		sb.WriteString("\n")
+		catLine += "\n"
+		lines = append(lines, catLine)
 
 		if len(entries) == 0 {
-			sb.WriteString("   <i>暂无内容</i>\n")
+			lines = append(lines, "   <i>暂无内容</i>\n")
 		} else {
 			for _, entry := range entries {
-				sb.WriteString(fmt.Sprintf("   • <a href=\"%s\">%s</a>", html.EscapeString(entry.MessageLink()), html.EscapeString(entry.Title)))
+				entryLine := fmt.Sprintf("   • <a href=\"%s\">%s</a>", html.EscapeString(entry.MessageLink()), html.EscapeString(entry.Title))
 				if entry.HasDirectLink() {
-					sb.WriteString(fmt.Sprintf(" <a href=\"%s\">[直达]</a>", html.EscapeString(entry.DirectLink)))
+					entryLine += fmt.Sprintf(" <a href=\"%s\">[直达]</a>", html.EscapeString(entry.DirectLink))
 				}
-				sb.WriteString("\n")
+				entryLine += "\n"
+				lines = append(lines, entryLine)
 			}
 		}
-		sb.WriteString("\n")
+
+		// 分类之间空行
+		lines = append(lines, "\n")
 	}
 
-	sb.WriteString("━━━━━━━━━━━━━━━\n")
-
-	return sb.String(), nil
+	return header, lines, footer, nil
+}
+
+// RenderPage 渲染指定页的 TOC 内容，返回内容、总页数
+func (m *Manager) RenderPage(page, charLimit int) (string, int, error) {
+	header, lines, footer, err := m.renderLines()
+	if err != nil {
+		return "", 0, err
+	}
+
+	// 页码行的最大长度预估（如 "📄 99 / 99\n"）
+	pageIndicatorLen := 15
+
+	headerLen := htmlTextLength(header)
+	footerLen := htmlTextLength(footer)
+	fixedLen := headerLen + footerLen + pageIndicatorLen
+
+	// 将行分配到各页
+	var pages [][]string
+	var currentPage []string
+	currentLen := fixedLen
+
+	for _, line := range lines {
+		lineLen := htmlTextLength(line)
+
+		// 如果当前页加上这行会超限，且当前页已有内容，则开新页
+		if currentLen+lineLen > charLimit && len(currentPage) > 0 {
+			pages = append(pages, currentPage)
+			currentPage = nil
+			currentLen = fixedLen
+		}
+
+		currentPage = append(currentPage, line)
+		currentLen += lineLen
+	}
+
+	// 最后一页
+	if len(currentPage) > 0 {
+		pages = append(pages, currentPage)
+	}
+
+	totalPages := len(pages)
+	if totalPages == 0 {
+		totalPages = 1
+		pages = [][]string{{}}
+	}
+
+	// clamp page
+	if page < 1 {
+		page = 1
+	}
+	if page > totalPages {
+		page = totalPages
+	}
+
+	// 组装当前页内容
+	var sb strings.Builder
+	sb.WriteString(header)
+	for _, line := range pages[page-1] {
+		sb.WriteString(line)
+	}
+	sb.WriteString(footer)
+
+	if totalPages > 1 {
+		sb.WriteString(fmt.Sprintf("📄 %d / %d\n", page, totalPages))
+	}
+
+	return sb.String(), totalPages, nil
+}
+
+// Render 渲染完整 TOC（兼容方法，返回第 1 页，使用 photo caption 限制）
+func (m *Manager) Render() (string, error) {
+	content, _, err := m.RenderPage(1, captionCharLimit)
+	return content, err
 }