fix: add DeduplicateChapters stub to test mocks to satisfy BookWriter interface

marked() returns string | Promise<string>; the previous cast 'as string'
silently passed a Promise object, which Svelte rendered as nothing.
Free users saw blank content even though SSR HTML was correct.

backend/internal/backend/handlers.go

@@ -569,6 +569,30 @@ func (s *Server) handleReindex(w http.ResponseWriter, r *http.Request) {
 	writeJSON(w, 0, map[string]any{"slug": slug, "indexed": count})
 }
 
+// handleDedupChapters handles POST /api/admin/dedup-chapters/{slug}.
+// Removes duplicate chapters_idx records for a book, keeping the latest record
+// per chapter number. Returns the number of duplicate records deleted.
+func (s *Server) handleDedupChapters(w http.ResponseWriter, r *http.Request) {
+	slug := r.PathValue("slug")
+	if slug == "" {
+		jsonError(w, http.StatusBadRequest, "missing slug")
+		return
+	}
+
+	deleted, err := s.deps.BookWriter.DeduplicateChapters(r.Context(), slug)
+	if err != nil {
+		s.deps.Log.Error("dedup-chapters failed", "slug", slug, "err", err)
+		writeJSON(w, http.StatusInternalServerError, map[string]any{
+			"error":   err.Error(),
+			"deleted": deleted,
+		})
+		return
+	}
+
+	s.deps.Log.Info("dedup-chapters complete", "slug", slug, "deleted", deleted)
+	writeJSON(w, 0, map[string]any{"slug": slug, "deleted": deleted})
+}
+
 // ── Audio ──────────────────────────────────────────────────────────────────────
 
 // handleAudioGenerate handles POST /api/audio/{slug}/{n}.

backend/internal/backend/server.go

@@ -204,6 +204,9 @@ func (s *Server) ListenAndServe(ctx context.Context) error {
 	mux.HandleFunc("POST /api/admin/text-gen/description", s.handleAdminTextGenDescription)
 	mux.HandleFunc("POST /api/admin/text-gen/description/apply", s.handleAdminTextGenApplyDescription)
 
+	// Admin data repair endpoints
+	mux.HandleFunc("POST /api/admin/dedup-chapters/{slug}", s.handleDedupChapters)
+
 	// Voices list
 	mux.HandleFunc("GET /api/voices", s.handleVoices)
 

backend/internal/bookstore/bookstore.go

@@ -35,6 +35,11 @@ type BookWriter interface {
 
 	// ChapterExists returns true if the markdown object for ref already exists.
 	ChapterExists(ctx context.Context, slug string, ref domain.ChapterRef) bool
+
+	// DeduplicateChapters removes duplicate chapters_idx records for slug,
+	// keeping only one record per chapter number (the one with the latest
+	// updated timestamp). Returns the number of duplicate records deleted.
+	DeduplicateChapters(ctx context.Context, slug string) (int, error)
 }
 
 // BookReader is the read side used by the backend to serve content.

backend/internal/bookstore/bookstore_test.go

@@ -39,8 +39,9 @@ func (m *mockStore) ReadChapter(_ context.Context, _ string, _ int) (string, err
 func (m *mockStore) ListChapters(_ context.Context, _ string) ([]domain.ChapterInfo, error) {
 	return nil, nil
 }
-func (m *mockStore) CountChapters(_ context.Context, _ string) int            { return 0 }
-func (m *mockStore) ReindexChapters(_ context.Context, _ string) (int, error) { return 0, nil }
+func (m *mockStore) CountChapters(_ context.Context, _ string) int                { return 0 }
+func (m *mockStore) ReindexChapters(_ context.Context, _ string) (int, error)     { return 0, nil }
+func (m *mockStore) DeduplicateChapters(_ context.Context, _ string) (int, error) { return 0, nil }
 
 // RankingStore
 func (m *mockStore) WriteRankingItem(_ context.Context, _ domain.RankingItem) error { return nil }
@@ -52,10 +53,10 @@ func (m *mockStore) RankingFreshEnough(_ context.Context, _ time.Duration) (bool
 }
 
 // AudioStore
-func (m *mockStore) AudioObjectKey(_ string, _ int, _ string) string          { return "" }
-func (m *mockStore) AudioObjectKeyExt(_ string, _ int, _, _ string) string    { return "" }
-func (m *mockStore) AudioExists(_ context.Context, _ string) bool             { return false }
-func (m *mockStore) PutAudio(_ context.Context, _ string, _ []byte) error     { return nil }
+func (m *mockStore) AudioObjectKey(_ string, _ int, _ string) string       { return "" }
+func (m *mockStore) AudioObjectKeyExt(_ string, _ int, _, _ string) string { return "" }
+func (m *mockStore) AudioExists(_ context.Context, _ string) bool          { return false }
+func (m *mockStore) PutAudio(_ context.Context, _ string, _ []byte) error  { return nil }
 func (m *mockStore) PutAudioStream(_ context.Context, _ string, _ io.Reader, _ int64, _ string) error {
 	return nil
 }

backend/internal/orchestrator/orchestrator_test.go

@@ -89,6 +89,8 @@ func (s *stubStore) WriteChapterRefs(_ context.Context, _ string, _ []domain.Cha
 	return nil
 }
 
+func (s *stubStore) DeduplicateChapters(_ context.Context, _ string) (int, error) { return 0, nil }
+
 func (s *stubStore) ChapterExists(_ context.Context, slug string, ref domain.ChapterRef) bool {
 	s.mu.Lock()
 	defer s.mu.Unlock()

backend/internal/runner/runner_test.go

@@ -94,6 +94,10 @@ func (s *stubBookWriter) ChapterExists(_ context.Context, _ string, _ domain.Cha
 	return false
 }
 
+func (s *stubBookWriter) DeduplicateChapters(_ context.Context, _ string) (int, error) {
+	return 0, nil
+}
+
 // stubBookReader satisfies bookstore.BookReader — returns a single chapter.
 type stubBookReader struct {
 	text    string

backend/internal/storage/store.go

@@ -130,7 +130,16 @@ func (s *Store) upsertChapterIdx(ctx context.Context, slug string, ref domain.Ch
 		return err
 	}
 	if len(items) == 0 {
-		return s.pb.post(ctx, "/api/collections/chapters_idx/records", payload, nil)
+		postErr := s.pb.post(ctx, "/api/collections/chapters_idx/records", payload, nil)
+		if postErr == nil {
+			return nil
+		}
+		// POST failed — a concurrent writer may have inserted the same slug+number.
+		// Re-fetch and fall through to PATCH (mirrors WriteMetadata retry pattern).
+		items, err = s.pb.listAll(ctx, "chapters_idx", filter, "")
+		if err != nil || len(items) == 0 {
+			return postErr // original POST error is more informative
+		}
 	}
 	var rec struct {
 		ID string `json:"id"`
@@ -139,6 +148,59 @@ func (s *Store) upsertChapterIdx(ctx context.Context, slug string, ref domain.Ch
 	return s.pb.patch(ctx, fmt.Sprintf("/api/collections/chapters_idx/records/%s", rec.ID), payload)
 }
 
+// DeduplicateChapters removes duplicate chapters_idx records for slug.
+// For each chapter number that has more than one record, it keeps the record
+// with the latest "updated" timestamp and deletes the rest.
+// Returns the number of records deleted.
+func (s *Store) DeduplicateChapters(ctx context.Context, slug string) (int, error) {
+	filter := fmt.Sprintf(`slug=%q`, slug)
+	items, err := s.pb.listAll(ctx, "chapters_idx", filter, "number")
+	if err != nil {
+		return 0, fmt.Errorf("DeduplicateChapters: list: %w", err)
+	}
+
+	type record struct {
+		ID      string `json:"id"`
+		Number  int    `json:"number"`
+		Updated string `json:"updated"`
+	}
+
+	// Group records by chapter number.
+	byNumber := make(map[int][]record)
+	for _, raw := range items {
+		var rec record
+		if err := json.Unmarshal(raw, &rec); err != nil || rec.ID == "" {
+			continue
+		}
+		byNumber[rec.Number] = append(byNumber[rec.Number], rec)
+	}
+
+	deleted := 0
+	for _, recs := range byNumber {
+		if len(recs) <= 1 {
+			continue
+		}
+		// Keep the record with the latest Updated timestamp; delete the rest.
+		keep := 0
+		for i := 1; i < len(recs); i++ {
+			if recs[i].Updated > recs[keep].Updated {
+				keep = i
+			}
+		}
+		for i, rec := range recs {
+			if i == keep {
+				continue
+			}
+			if delErr := s.pb.delete(ctx, fmt.Sprintf("/api/collections/chapters_idx/records/%s", rec.ID)); delErr != nil {
+				s.log.Warn("DeduplicateChapters: delete failed", "slug", slug, "number", rec.Number, "id", rec.ID, "err", delErr)
+				continue
+			}
+			deleted++
+		}
+	}
+	return deleted, nil
+}
+
 // ── BookReader ────────────────────────────────────────────────────────────────
 
 type pbBook struct {

ui/src/routes/books/[slug]/chapters/[n]/+page.server.ts

@@ -154,7 +154,7 @@ export const load: PageServerLoad = async ({ params, url, locals }) => {
 			error(res.status === 404 ? 404 : 502, res.status === 404 ? `Chapter ${n} not found` : 'Could not fetch chapter content');
 		}
 		const markdown = await res.text();
-		html = marked(markdown) as string;
+		html = await marked(markdown);
 	} catch (e) {
 		if (e instanceof Error && 'status' in e) throw e;
 		// Don't hard-fail — show empty content with error message