Number of channels the registry currently holds.

The counterpart to IWebSocketService.roomCount, and worth watching rather than merely reporting: a channel is created by ISseService.channel and nothing reclaims it, so for the life of a running application this number only rises. A steadily climbing count means channel names are being derived from unbounded input — use ISseService.peek on any path that reads a caller-supplied name.

The one thing that lowers it is shutdown: the plugin's onClose discards every channel, so a probe racing teardown reads 0 rather than the last live value.