Make silent render failures loud, off the hot path - #339

Build success
✅ Preparing build machine 0:00:23 view logs
✅ Fetching app sources 0:00:04 view logs
✅ Restoring cache 0:00:07 view logs
✅ Installing SDKs 0:01:34 view logs
✅ Select the Flutter channel 0:00:00 view logs
✅ Flutter and engine revision 0:00:01 view logs
✅ Assert the build holds no credentials 0:00:00 view logs
✅ Generate the iOS project 0:00:03 view logs
✅ Enable native and data assets 0:00:01 view logs
✅ Resolve the workspace 0:00:01 view logs
✅ Boot the simulator 0:01:12 view logs
✅ Render smoke scenes 0:04:28 view logs
✅ Publish the render status 0:00:00 view logs
✅ Publishing 0:00:02 view logs
✅ Cleaning up 0:00:00 view logs

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