pool protobuf marshal buffers to reduce allocations

Use sync.Pool to reuse 4KB byte slices for protobuf marshaling via
MarshalAppend instead of allocating fresh buffers per result message.
Reduces GC pressure under high-throughput polling.

agent.go

@@ -118,13 +118,20 @@ func runSession(ctx context.Context, baseURL, token string) error {
 		}
 	}
 
+	bufPool := &sync.Pool{
+		New: func() any { return make([]byte, 0, 4096) },
+	}
+
 	sendBinaryResult := func(event string, msg proto.Message) {
-		bin, err := proto.Marshal(msg)
+		buf := bufPool.Get().([]byte)[:0]
+		bin, err := proto.MarshalOptions{}.MarshalAppend(buf, msg)
 		if err != nil {
 			slog.Error("marshal protobuf", "error", err)
 			return
 		}
-		payload, _ := json.Marshal(map[string]string{"binary": base64.StdEncoding.EncodeToString(bin)})
+		encoded := base64.StdEncoding.EncodeToString(bin)
+		bufPool.Put(bin[:0])
+		payload, _ := json.Marshal(map[string]string{"binary": encoded})
 		sendMsg(event, payload)
 	}