diff --git a/apps/indexer/src/analyzer.rs b/apps/indexer/src/analyzer.rs
index 02893e1..dba467d 100644
--- a/apps/indexer/src/analyzer.rs
+++ b/apps/indexer/src/analyzer.rs
@@ -388,16 +388,14 @@ pub async fn regenerate_thumbnails(
 }
 
 /// Delete orphaned thumbnail files (books deleted in full_rebuild get new UUIDs).
-pub async fn cleanup_orphaned_thumbnails(
-    state: &AppState,
-    library_id: Option<Uuid>,
-) -> Result<()> {
+pub async fn cleanup_orphaned_thumbnails(state: &AppState) -> Result<()> {
     let config = load_thumbnail_config(&state.pool).await;
 
+    // Load ALL book IDs across all libraries — we need the complete set to avoid
+    // deleting thumbnails that belong to other libraries during a per-library rebuild.
     let existing_book_ids: std::collections::HashSet<Uuid> = sqlx::query_scalar(
-        r#"SELECT id FROM books WHERE (library_id = $1 OR $1 IS NULL)"#,
+        r#"SELECT id FROM books"#,
     )
-    .bind(library_id)
     .fetch_all(&state.pool)
     .await
     .unwrap_or_default()
diff --git a/apps/indexer/src/job.rs b/apps/indexer/src/job.rs
index 175adb3..db051a6 100644
--- a/apps/indexer/src/job.rs
+++ b/apps/indexer/src/job.rs
@@ -315,7 +315,7 @@ pub async fn process_job(
 
     // For full rebuild: clean up orphaned thumbnail files (old UUIDs)
     if is_full_rebuild {
-        analyzer::cleanup_orphaned_thumbnails(state, target_library_id).await?;
+        analyzer::cleanup_orphaned_thumbnails(state).await?;
     }
 
     // Phase 2: Analysis (extract page_count + thumbnails for new/updated books)
diff --git a/infra/smoke.sh b/infra/smoke.sh
index 426e26a..d130e35 100755
--- a/infra/smoke.sh
+++ b/infra/smoke.sh
@@ -122,6 +122,62 @@ else
   exit 1
 fi
 
+# ─── full_rebuild par library ne casse pas les thumbnails des autres ──────────
+#
+# Régression : cleanup_orphaned_thumbnails chargeait uniquement les book IDs
+# de la library en cours de rebuild, supprimant les thumbnails des autres.
+#
+# Ce test nécessite au moins 2 libraries activées avec des livres indexés.
+
+echo "[smoke] test: full_rebuild per-library does not destroy other libraries thumbnails"
+LIBRARIES_JSON="$(auth "$BASE_API/libraries")"
+LIBRARY_COUNT="$(LIBRARIES_JSON="$LIBRARIES_JSON" python3 -c "import json,os; libs=json.loads(os.environ['LIBRARIES_JSON']); print(len(libs) if isinstance(libs,list) else 0)")"
+
+if [ "${LIBRARY_COUNT:-0}" -lt 2 ]; then
+  echo "[smoke] SKIP: need at least 2 libraries (found ${LIBRARY_COUNT:-0})"
+else
+  # Extraire les 2 premiers IDs de library
+  LIB_A="$(LIBRARIES_JSON="$LIBRARIES_JSON" python3 -c "import json,os; libs=json.loads(os.environ['LIBRARIES_JSON']); print(libs[0]['id'])")"
+  LIB_B="$(LIBRARIES_JSON="$LIBRARIES_JSON" python3 -c "import json,os; libs=json.loads(os.environ['LIBRARIES_JSON']); print(libs[1]['id'])")"
+  echo "[smoke] library A = $LIB_A, library B = $LIB_B"
+
+  # Compter les thumbnails de library B avant le rebuild de A
+  BOOKS_B_BEFORE="$(auth "$BASE_API/books?library_id=$LIB_B")"
+  THUMBS_BEFORE="$(BOOKS_B_BEFORE="$BOOKS_B_BEFORE" python3 -c "
+import json, os
+items = json.loads(os.environ['BOOKS_B_BEFORE']).get('items') or []
+print(sum(1 for b in items if b.get('thumbnail_url')))
+")"
+  echo "[smoke] library B: $THUMBS_BEFORE book(s) with thumbnail before rebuild of A"
+
+  if [ "${THUMBS_BEFORE:-0}" -eq 0 ]; then
+    echo "[smoke] SKIP: library B has no thumbnails to protect, test not meaningful"
+  else
+    # Lancer un full_rebuild sur library A uniquement
+    REBUILD_A_ID="$(auth -X POST -H "Content-Type: application/json" \
+      -d "{\"library_id\":\"$LIB_A\",\"full\":true}" \
+      "$BASE_API/index/rebuild" | python3 -c "import sys,json; print(json.load(sys.stdin)['id'])")"
+    echo "[smoke] full_rebuild library A job id: $REBUILD_A_ID"
+    wait_job "$REBUILD_A_ID" "full_rebuild library A"
+
+    # Vérifier que les thumbnails de library B sont intacts
+    BOOKS_B_AFTER="$(auth "$BASE_API/books?library_id=$LIB_B")"
+    THUMBS_AFTER="$(BOOKS_B_AFTER="$BOOKS_B_AFTER" python3 -c "
+import json, os
+items = json.loads(os.environ['BOOKS_B_AFTER']).get('items') or []
+print(sum(1 for b in items if b.get('thumbnail_url')))
+")"
+    echo "[smoke] library B: $THUMBS_AFTER book(s) with thumbnail after rebuild of A"
+
+    if [ "$THUMBS_AFTER" -lt "$THUMBS_BEFORE" ]; then
+      echo "[smoke] FAIL: full_rebuild of library A destroyed thumbnails of library B ($THUMBS_BEFORE → $THUMBS_AFTER)"
+      exit 1
+    else
+      echo "[smoke] OK: library B thumbnails preserved ($THUMBS_BEFORE → $THUMBS_AFTER)"
+    fi
+  fi
+fi
+
 # ─── metrics ─────────────────────────────────────────────────────────────────
 
 echo "[smoke] metrics"