fix(jellyfin): memoize stable server Id and cover get-or-create path

server/jellyfin/api.go

@@ -3,6 +3,7 @@ package jellyfin
 import (
 	"encoding/json"
 	"net/http"
+	"sync"
 
 	"github.com/go-chi/chi/v5"
 	"github.com/navidrome/navidrome/core"
@@ -23,6 +24,8 @@ type Router struct {
 	players          core.Players
 	scrobbler        scrobbler.PlayTracker
 	playlists        playlists.Playlists
+	serverIDOnce     sync.Once
+	serverIDVal      string
 }
 
 func New(ds model.DataStore, artwork artwork.Artwork, streamer stream.MediaStreamer,

server/jellyfin/system.go

@@ -22,18 +22,25 @@ func (api *Router) serverName() string {
 // the same way core/metrics/insights.go derives its InsightsID. Jellyfin clients cache
 // ServerId across sessions, so a per-process value would break re-authentication.
 // api.ds is nil only in unit tests that construct Router{} directly; New() always sets it.
+//
+// Resolution happens once per Router (sync.Once), so concurrent first-boot requests can't
+// each generate and persist a different UUID before the row settles.
 func (api *Router) serverID(ctx context.Context) string {
-	if api.ds == nil {
-		return uuid.NewString()
-	}
-	id, err := api.ds.Property(ctx).Get(consts.JellyfinServerIDKey)
-	if err != nil {
-		id = uuid.NewString()
-		if err := api.ds.Property(ctx).Put(consts.JellyfinServerIDKey, id); err != nil {
-			log.Error(ctx, "Jellyfin API: could not persist server id", err)
+	api.serverIDOnce.Do(func() {
+		if api.ds == nil {
+			api.serverIDVal = uuid.NewString()
+			return
 		}
-	}
-	return id
+		id, err := api.ds.Property(ctx).Get(consts.JellyfinServerIDKey)
+		if err != nil {
+			id = uuid.NewString()
+			if err := api.ds.Property(ctx).Put(consts.JellyfinServerIDKey, id); err != nil {
+				log.Error(ctx, "Jellyfin API: could not persist server id", err)
+			}
+		}
+		api.serverIDVal = id
+	})
+	return api.serverIDVal
 }
 
 func (api *Router) publicInfo(ctx context.Context) dto.PublicSystemInfo {

server/jellyfin/system_test.go

@@ -1,11 +1,13 @@
 package jellyfin
 
 import (
+	"context"
 	"encoding/json"
 	"net/http"
 	"net/http/httptest"
 
 	"github.com/navidrome/navidrome/server/jellyfin/dto"
+	"github.com/navidrome/navidrome/tests"
 	. "github.com/onsi/ginkgo/v2"
 	. "github.com/onsi/gomega"
 )
@@ -49,4 +51,30 @@ var _ = Describe("System", func() {
 		Expect(json.Unmarshal(w.Body.Bytes(), &enabled)).To(Succeed())
 		Expect(enabled).To(BeFalse())
 	})
+
+	Context("serverID with a real DataStore", func() {
+		var ctx context.Context
+		var ds *tests.MockDataStore
+
+		BeforeEach(func() {
+			ctx = context.Background()
+			ds = &tests.MockDataStore{}
+		})
+
+		It("persists the generated id so it can be read back by another Router sharing the same DataStore", func() {
+			first := &Router{ds: ds}
+			id := first.serverID(ctx)
+			Expect(id).ToNot(BeEmpty())
+
+			second := &Router{ds: ds}
+			Expect(second.serverID(ctx)).To(Equal(id))
+		})
+
+		It("memoizes the id across repeated calls on the same Router", func() {
+			r := &Router{ds: ds}
+			id := r.serverID(ctx)
+			Expect(r.serverID(ctx)).To(Equal(id))
+			Expect(r.serverID(ctx)).To(Equal(id))
+		})
+	})
 })