Nest camera.snapshot returns placeholder image instead of real frame for WebRTC-only devices

The problem For Nest cameras/doorbells whose CameraLiveStream trait reports supportedProtocols: ["WEB_RTC"] only (i.e. devices migrated to the Google Home app, no RTSP support), any request for a still frame — via camera.snapshot, /api/camera_proxy/<entity>, or /api/camera_proxy_stream/<entity> — returns a static placeholder image, not a real frame from the camera. This fails silently: • HTTP status is 200 OK • Content-Type header says image/jpeg • The entity state is idle/streaming (not unavailable), so nothing looks wrong at a glance • The response is always the exact same byte size regardless of what the camera is actually pointed at, or what time of day it is Inspecting the actual response bytes shows it isn't a JPEG at all — it's a PNG (\x89PNG\r\n\x1a\n magic number) mislabeled with a Content-Type: image/jpeg header. This looks like a generic "no signal"/placeholder graphic being returned instead of a real deco…