fix(pagination): recalculate with exact text_rect dims inside CentralPanel, validate current_page

src/reader.rs

@@ -60,11 +60,6 @@ pub fn reading_view(
 
       let colors = theme::reader_colors(theme);
 
-     // 工具栏之前预估文本区尺寸完成分页（扣除边距 48px + 工具条 ~60px）
-     let panel_size = ui.available_size();
-     let est_width = (panel_size.x - 48.0).max(100.0);
-     let est_height = (panel_size.y - 60.0).max(200.0);
-     recalculate_pages(book, style.font_size, style.line_height(), est_width, est_height);
      let has_bookmark = bookmarks.iter().any(|b| b.section == *current_section && b.page == *current_page);
 
     // --- Sidebar (TOC + Bookmarks) ---
@@ -229,6 +224,17 @@ egui::ComboBox::from_id_salt("bg_type_selector")
               egui::vec2((rect.width() - inset * 2.0).max(100.0), rect.height()),
           );
 
+          // 用实际文本区宽高重新分页（包含侧边栏、工具条等已占空间后的精确值）
+          recalculate_pages(book, style.font_size, style.line_height(), text_rect.width(), text_rect.height());
+
+          // 确保 current_page 在新分页后仍在有效范围内
+          if let Some(section) = book.sections.get(*current_section) {
+              let max_page = section.pages.len().saturating_sub(2);
+              if *current_page > max_page {
+                  *current_page = max_page;
+              }
+          }
+
          if let Some(section) = book.sections.get(*current_section) {
             if *current_page < section.pages.len().saturating_sub(1) {
                 let start = section.pages[*current_page];