Reads the stream metrics Lumana collects from Cores — resolution, frame rate, codec, bitrate and packet drop, for the main stream and the substream of each camera — together with the load and the network state of each Core. Unlike the other troubleshooting endpoints this one does not talk to the device: it reads metrics already collected, so it answers immediately and works for a Core that is currently offline, returning whatever was last observed. Use it to see whether a camera is delivering the stream it is configured for, and whether the Core carrying it is near its capacity. Metrics are collected over a five-minute window; a camera provisioned more recently than that, or one whose stream is down, comes back with null fields rather than being omitted.