fix(node-sync): don't delete a node's central inbounds when its snapshot is empty

The central-inbound sweep deletes any central inbound whose tag is absent from the node's snapshot, with no guard for an empty snapshot. A node mid-restart or with a transient DB error (e.g. Postgres 57P01) can return an empty inbound list with success=true, which wiped all of that node's central inbounds and their clients (and reset traffic history on re-create) — observed on the Germany node: 0 clients but still 44 online (online survives because it comes from the snapshot's online tree, not the central inbound). Skip the sweep entirely when the snapshot reports zero inbounds; a real per-inbound deletion still sweeps via a non-empty snapshot that omits one tag.

internal/web/service/inbound_node.go

@@ -499,6 +499,15 @@ func (s *InboundService) setRemoteTrafficLocked(nodeID int, snap *runtime.Traffi
 		if dirty {
 			continue
 		}
+		if len(snapTags) == 0 {
+			// A node mid-restart or with a transient DB error can return an empty
+			// inbound list with success=true. Treat "zero inbounds reported" as
+			// "nothing to say", not "delete all my inbounds" — otherwise a blip
+			// wipes the node's central inbounds and every client on them (and
+			// resets traffic history on re-create). A real per-inbound deletion
+			// still sweeps, because the node keeps reporting its other inbounds.
+			continue
+		}
 		if _, kept := snapTags[c.Tag]; kept {
 			continue
 		}

internal/web/service/node_origin_guid_test.go

@@ -131,6 +131,43 @@ func TestSetRemoteTraffic_RemapsClonedNodeOwnGuidOrigin(t *testing.T) {
 	}
 }
 
+// A node mid-restart can return an empty inbound list with success=true. The
+// sync must NOT treat that as "delete all my inbounds" — otherwise a blip wipes
+// the node's central inbounds and every client on them (what happened to the
+// Germany node: 0 clients but still online).
+func TestSetRemoteTraffic_EmptySnapshotKeepsCentralInbounds(t *testing.T) {
+	setupConflictDB(t)
+	db := database.GetDB()
+
+	const nodeID = 1
+	if err := db.Create(&model.Node{
+		Id: nodeID, Name: "n", Address: "10.0.0.1", Port: 2053, ApiToken: "t", Guid: "g",
+	}).Error; err != nil {
+		t.Fatalf("create node: %v", err)
+	}
+	nidPtr := nodeID
+	if err := db.Create(&model.Inbound{
+		UserId: 1, NodeID: &nidPtr, Tag: "remote-in", Enable: true,
+		Port: 443, Protocol: model.VLESS, Settings: `{"clients":[]}`,
+	}).Error; err != nil {
+		t.Fatalf("create central inbound: %v", err)
+	}
+
+	// Empty snapshot — the node reported no inbounds this cycle.
+	svc := InboundService{}
+	if _, err := svc.setRemoteTrafficLocked(nodeID, &runtime.TrafficSnapshot{}, false); err != nil {
+		t.Fatalf("setRemoteTrafficLocked: %v", err)
+	}
+
+	var count int64
+	if err := db.Model(&model.Inbound{}).Where("tag = ?", "remote-in").Count(&count).Error; err != nil {
+		t.Fatalf("count inbounds: %v", err)
+	}
+	if count != 1 {
+		t.Fatalf("empty snapshot must not delete the central inbound; got count = %d", count)
+	}
+}
+
 func TestSetRemoteTraffic_PreservesLocalShareAddressStrategy(t *testing.T) {
 	setupConflictDB(t)
 	db := database.GetDB()