feat: include series_count and thumbnail_book_ids in libraries API response

Eliminates N+1 sequential fetchSeries calls on the libraries page by
returning series count and up to 5 thumbnail book IDs (one per series)
directly from GET /libraries.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/api/src/libraries.rs

@@ -26,6 +26,10 @@ pub struct LibraryResponse {
     pub metadata_refresh_mode: String,
     #[schema(value_type = Option<String>)]
     pub next_metadata_refresh_at: Option<chrono::DateTime<chrono::Utc>>,
+    pub series_count: i64,
+    /// First book IDs from up to 5 distinct series (for thumbnail fan display)
+    #[schema(value_type = Vec<String>)]
+    pub thumbnail_book_ids: Vec<Uuid>,
 }
 
 #[derive(Deserialize, ToSchema)]
@@ -51,7 +55,21 @@ pub struct CreateLibraryRequest {
 pub async fn list_libraries(State(state): State<AppState>) -> Result<Json<Vec<LibraryResponse>>, ApiError> {
     let rows = sqlx::query(
         "SELECT l.id, l.name, l.root_path, l.enabled, l.monitor_enabled, l.scan_mode, l.next_scan_at, l.watcher_enabled, l.metadata_provider, l.fallback_metadata_provider, l.metadata_refresh_mode, l.next_metadata_refresh_at,
-                (SELECT COUNT(*) FROM books b WHERE b.library_id = l.id) as book_count
+                (SELECT COUNT(*) FROM books b WHERE b.library_id = l.id) as book_count,
+                (SELECT COUNT(DISTINCT COALESCE(NULLIF(b.series, ''), 'unclassified')) FROM books b WHERE b.library_id = l.id) as series_count,
+                COALESCE((
+                    SELECT ARRAY_AGG(first_id ORDER BY series_name)
+                    FROM (
+                        SELECT DISTINCT ON (COALESCE(NULLIF(b.series, ''), 'unclassified'))
+                            COALESCE(NULLIF(b.series, ''), 'unclassified') as series_name,
+                            b.id as first_id
+                        FROM books b
+                        WHERE b.library_id = l.id
+                        ORDER BY COALESCE(NULLIF(b.series, ''), 'unclassified'),
+                            b.volume NULLS LAST, b.title ASC
+                        LIMIT 5
+                    ) sub
+                ), ARRAY[]::uuid[]) as thumbnail_book_ids
          FROM libraries l ORDER BY l.created_at DESC"
     )
         .fetch_all(&state.pool)
@@ -65,6 +83,7 @@ pub async fn list_libraries(State(state): State<AppState>) -> Result<Json<Vec<Li
             root_path: row.get("root_path"),
             enabled: row.get("enabled"),
             book_count: row.get("book_count"),
+            series_count: row.get("series_count"),
             monitor_enabled: row.get("monitor_enabled"),
             scan_mode: row.get("scan_mode"),
             next_scan_at: row.get("next_scan_at"),
@@ -73,6 +92,7 @@ pub async fn list_libraries(State(state): State<AppState>) -> Result<Json<Vec<Li
             fallback_metadata_provider: row.get("fallback_metadata_provider"),
             metadata_refresh_mode: row.get("metadata_refresh_mode"),
             next_metadata_refresh_at: row.get("next_metadata_refresh_at"),
+            thumbnail_book_ids: row.get("thumbnail_book_ids"),
         })
         .collect();
 
@@ -120,6 +140,7 @@ pub async fn create_library(
         root_path,
         enabled: true,
         book_count: 0,
+        series_count: 0,
         monitor_enabled: false,
         scan_mode: "manual".to_string(),
         next_scan_at: None,
@@ -128,6 +149,7 @@ pub async fn create_library(
         fallback_metadata_provider: None,
         metadata_refresh_mode: "manual".to_string(),
         next_metadata_refresh_at: None,
+        thumbnail_book_ids: vec![],
     }))
 }
 
@@ -337,12 +359,29 @@ pub async fn update_monitoring(
         .fetch_one(&state.pool)
         .await?;
 
+    let series_count: i64 = sqlx::query_scalar("SELECT COUNT(DISTINCT COALESCE(NULLIF(series, ''), 'unclassified')) FROM books WHERE library_id = $1")
+        .bind(library_id)
+        .fetch_one(&state.pool)
+        .await?;
+
+    let thumbnail_book_ids: Vec<Uuid> = sqlx::query_scalar(
+        "SELECT b.id FROM books b
+         WHERE b.library_id = $1
+         ORDER BY COALESCE(NULLIF(b.series, ''), 'unclassified'), b.volume NULLS LAST, b.title ASC
+         LIMIT 5"
+    )
+    .bind(library_id)
+    .fetch_all(&state.pool)
+    .await
+    .unwrap_or_default();
+
     Ok(Json(LibraryResponse {
         id: row.get("id"),
         name: row.get("name"),
         root_path: row.get("root_path"),
         enabled: row.get("enabled"),
         book_count,
+        series_count,
         monitor_enabled: row.get("monitor_enabled"),
         scan_mode: row.get("scan_mode"),
         next_scan_at: row.get("next_scan_at"),
@@ -351,6 +390,7 @@ pub async fn update_monitoring(
         fallback_metadata_provider: row.get("fallback_metadata_provider"),
         metadata_refresh_mode: row.get("metadata_refresh_mode"),
         next_metadata_refresh_at: row.get("next_metadata_refresh_at"),
+        thumbnail_book_ids,
     }))
 }
 
@@ -403,12 +443,29 @@ pub async fn update_metadata_provider(
         .fetch_one(&state.pool)
         .await?;
 
+    let series_count: i64 = sqlx::query_scalar("SELECT COUNT(DISTINCT COALESCE(NULLIF(series, ''), 'unclassified')) FROM books WHERE library_id = $1")
+        .bind(library_id)
+        .fetch_one(&state.pool)
+        .await?;
+
+    let thumbnail_book_ids: Vec<Uuid> = sqlx::query_scalar(
+        "SELECT b.id FROM books b
+         WHERE b.library_id = $1
+         ORDER BY COALESCE(NULLIF(b.series, ''), 'unclassified'), b.volume NULLS LAST, b.title ASC
+         LIMIT 5"
+    )
+    .bind(library_id)
+    .fetch_all(&state.pool)
+    .await
+    .unwrap_or_default();
+
     Ok(Json(LibraryResponse {
         id: row.get("id"),
         name: row.get("name"),
         root_path: row.get("root_path"),
         enabled: row.get("enabled"),
         book_count,
+        series_count,
         monitor_enabled: row.get("monitor_enabled"),
         scan_mode: row.get("scan_mode"),
         next_scan_at: row.get("next_scan_at"),
@@ -417,5 +474,6 @@ pub async fn update_metadata_provider(
         fallback_metadata_provider: row.get("fallback_metadata_provider"),
         metadata_refresh_mode: row.get("metadata_refresh_mode"),
         next_metadata_refresh_at: row.get("next_metadata_refresh_at"),
+        thumbnail_book_ids,
     }))
 }

apps/backoffice/app/libraries/page.tsx

@@ -1,6 +1,6 @@
 import { revalidatePath } from "next/cache";
 import Link from "next/link";
-import { listFolders, createLibrary, deleteLibrary, fetchLibraries, fetchSeries, getBookCoverUrl, LibraryDto, FolderItem } from "../../lib/api";
+import { listFolders, createLibrary, deleteLibrary, fetchLibraries, getBookCoverUrl, LibraryDto, FolderItem } from "../../lib/api";
 import type { TranslationKey } from "../../lib/i18n/fr";
 import { getServerTranslations } from "../../lib/i18n/server";
 import { LibraryActions } from "../components/LibraryActions";
@@ -33,27 +33,13 @@ export default async function LibrariesPage() {
     listFolders().catch(() => [] as FolderItem[])
   ]);
 
-  const seriesData = await Promise.all(
+  const thumbnailMap = new Map(
-    libraries.map(async (lib) => {
+    libraries.map(lib => [
-      try {
+      lib.id,
-        const seriesPage = await fetchSeries(lib.id, 1, 6);
+      (lib.thumbnail_book_ids || []).map(bookId => getBookCoverUrl(bookId)),
-        return {
+    ])
-          id: lib.id,
-          count: seriesPage.total,
-          thumbnails: seriesPage.items
-            .map(s => s.first_book_id)
-            .filter(Boolean)
-            .slice(0, 4)
-            .map(bookId => getBookCoverUrl(bookId)),
-        };
-      } catch {
-        return { id: lib.id, count: 0, thumbnails: [] as string[] };
-      }
-    })
   );
 
-  const seriesMap = new Map(seriesData.map(s => [s.id, s]));
-
   async function addLibrary(formData: FormData) {
     "use server";
     const name = formData.get("name") as string;
@@ -96,9 +82,7 @@ export default async function LibrariesPage() {
       {/* Libraries Grid */}
       <div className="grid grid-cols-1 md:grid-cols-2 lg:grid-cols-3 gap-4">
         {libraries.map((lib) => {
-          const series = seriesMap.get(lib.id);
+          const thumbnails = thumbnailMap.get(lib.id) || [];
-          const seriesCount = series?.count || 0;
-          const thumbnails = series?.thumbnails || [];
           return (
             <Card key={lib.id} className="flex flex-col overflow-hidden">
               {/* Thumbnail fan */}
@@ -183,7 +167,7 @@ export default async function LibrariesPage() {
                     href={`/libraries/${lib.id}/series`}
                     className="text-center p-2.5 bg-muted/50 rounded-lg hover:bg-accent transition-colors duration-200"
                   >
-                    <span className="block text-2xl font-bold text-foreground">{seriesCount}</span>
+                    <span className="block text-2xl font-bold text-foreground">{lib.series_count}</span>
                     <span className="text-xs text-muted-foreground">{t("libraries.series")}</span>
                   </Link>
                 </div>

apps/backoffice/lib/api.ts

@@ -12,6 +12,8 @@ export type LibraryDto = {
   fallback_metadata_provider: string | null;
   metadata_refresh_mode: string;
   next_metadata_refresh_at: string | null;
+  series_count: number;
+  thumbnail_book_ids: string[];
 };
 
 export type IndexJobDto = {