Function sync_response_is_empty 

pub fn sync_response_is_empty(value: &Value) -> bool

“No rooms/account-data/to-device/device-lists changes, no typing/receipt change” (P10 brief) — device_one_time_keys_count/ device_unused_fallback_key_types are deliberately NOT part of this check: they are static per-device facts always present, never a “new since last time” signal.