1 files changed, 11 insertions, 2 deletions
diff --git a/src/html.zig b/src/html.zig
index ec9ecfd..fe7f287 100644
--- a/src/html.zig
+++ b/src/html.zig
@@ -63,10 +63,16 @@ pub fn transform(allocator: std.mem.Allocator, page: []const u8) !Document {
     const no_sidebar = try removeNavigation(allocator, escaped);
     defer allocator.free(no_sidebar);
 
+    // Section headings link back to their entry in the removed sidebar
+    // (`href="#toc-X"`); redirect those to the matching anchors now in nav.xhtml,
+    // otherwise they are dangling fragments (epubcheck RSC-012, breaks Kindle).
+    const relinked = try std.mem.replaceOwned(u8, allocator, no_sidebar, "href=\"#toc-", "href=\"nav.xhtml#toc-");
+    defer allocator.free(relinked);
+
     var out: std.Io.Writer.Allocating = .init(allocator);
     defer out.deinit();
     try out.writer.writeAll(xml_decl);
-    try writeWithFixups(&out.writer, no_sidebar);
+    try writeWithFixups(&out.writer, relinked);
 
     const content = try out.toOwnedSlice();
     assert(std.mem.startsWith(u8, content, "<?xml"));
@@ -536,7 +542,7 @@ test "transform extracts TOC and removes the navigation sidebar" {
         "<ul><li><a id=\"toc-Intro\" href=\"#Intro\">Intro</a>" ++
         "<ul><li><a href=\"#Sub\">Sub</a></li></ul></li></ul>" ++
         "</nav></div>" ++
-        "<main id=\"contents\"><h2 id=\"Intro\">Intro</h2><p>body</p></main>" ++
+        "<main id=\"contents\"><h2 id=\"Intro\"><a href=\"#toc-Intro\">Intro</a></h2><p>body</p></main>" ++
         "</div></body></html>";
 
     var doc = try transform(gpa, page);
@@ -549,6 +555,9 @@ test "transform extracts TOC and removes the navigation sidebar" {
     try std.testing.expect(std.mem.indexOf(u8, doc.content, "<main id=\"contents\">") != null);
     try std.testing.expect(std.mem.indexOf(u8, doc.content, "<h2 id=\"Intro\">") != null);
     try std.testing.expect(isWellFormed(doc.content));
+    // Back-to-contents link is redirected to the nav document (no dangling fragment).
+    try std.testing.expect(std.mem.indexOf(u8, doc.content, "href=\"nav.xhtml#toc-Intro\"") != null);
+    try std.testing.expect(std.mem.indexOf(u8, doc.content, "href=\"#toc-Intro\"") == null);
 
     // TOC extracted, ul->ol, links rewritten into the content document.
     try std.testing.expect(doc.toc != null);