So if the battery dies, and it locks by local solenoid. Whats the use of running an emergency cable for when the battery dies. Seems the cable would be useless if it locks by local solenoid.

The levers that pull the release cables are prevented from moving, however you can still pull the release cable via other means if you can get to it. There is a emergency cable that is looped around the main release cable; pulling it will unlock your frunk latch.

IIRC this cable is stuffed under the right front fender liner...( please verify as I changed this many years back) and hard to get to. Many have rerouted such that it can be used when needed.