Held inputs

A right click in the open air never reaches the server

The game tells the server about a right click only when it lands on something: a block, an entity, or an item that has a use. A right click with an empty hand in the open air sends nothing. An ability that is fired with the use key - a cannon grafted on the arm, a held beam - therefore cannot be written on the server alone, and an addon should not open a network channel of its own for one key.

HeldInputs carries it:

// Client, once (client set-up or a client-only class): when this addon wants the key reported.
HeldInputs.watch(HeldInputs.Input.USE,
        player -> MyMorphs.CANNON.get().isActive(player) && player.getMainHandItem().isEmpty());

// Server, in the ability's continuity tick.
if (HeldInputs.isHeld(player, HeldInputs.Input.USE)) {
    fire(player);
}

Two keys can be watched: Input.USE (right click by default) and Input.ATTACK (left click).

What is sent, and when

nothing is watched	nothing is sent, ever
a watch says yes, the key goes down	one packet: held
the key goes up, a screen opens, or every watch says no	one packet: released
the key stays down	nothing more

The predicate handed to watch is asked every client tick. It can therefore also say "not now" - the crosshair is on a chest, an item came into the hand - and the key then counts as released until it says yes again. That is how an addon lets a normal interaction win over its ability.

On the server the state is forgotten when the player logs out, respawns or changes dimension; the client starts again from nothing at the same moments.

⚠️ It is a wish, not a fact

What isHeld answers is what the client said. Treat it as a key press: check on the server whatever the ability needs - the form still active, the hand still empty, the delay between two shots, the ammunition. A modified client can claim the key is held; it must not be able to claim more than that.

⚠️ It changed the network protocol

HeldInputPacket was added in protocol version 6: a client and a server must both carry a version of the library that has it, as for every packet added to AkumaNetwork.