don't transmit nil predecessors

chord/httpnode/httpnode.go

@@ -43,5 +43,5 @@ func readResponse[T any](r *http.Response) (x T, err error) {
 
 type neighbors struct {
 	Succ []netip.AddrPort `json:"succ"`
-	Pred netip.AddrPort   `json:"pred"`
+	Pred netip.AddrPort   `json:"pred,omitzero"`
 }

chord/httpnode/server.go

@@ -13,6 +13,8 @@ type Node struct {
 	// self is the node topology this server represents.
 	self *chord.Node
 	// client is the Chord client for forwarding queries to other nodes.
+	// TODO(branden): really we should have a client per peer so that we can
+	// interchange protocols
 	client chord.Client
 }