[1.15.2] Capability state reset upon loading the game

[T-Dark_]

I'm trying to implement a basic teleportation staff. I managed to get the basic tp functionality working, and am now trying to make it require electricity.

I'm overriding initCapabilities in the item's class, and I managed to get a capability provider working. The cap works perfectly fine, and it updates the itemstack's nbt data correctly, until I close the game and reload it. When I do that, the capability resets its energy to 0, without updating the NBT data.

What I would like to get is an item that doesn't lose all of its energy because I closed the game.

I already tried to set the cap's energy based on the nbt data of the itemstack, but that only exists on the server ("server thread"). On the client ("render thread"), it's null.
 

Here is the code, on github.

Can anyone fill me in as to what I'm missing?

[T-Dark_]

I updated my code. Now I only create the LazyOptional in the ICapabilityProvider constructor, and then always use the same. The other problem has changed, but it's still not correct.

 

I implemented INBTSerializable, but the capability's energy is still reset whenever I load the game. The bright side is that the nbt is no longer out of sync: it is reset to 0 as well.

 

What am I doing wrong? Why is the tag reset to 0, as opposed to remaining what it was when I last saved the game?

[T-Dark_]

Based on the output of /data get entity @s Inventory[0]

[11:34:29] [Render thread/INFO] [minecraft/NewChatGui]: [CHAT] Dev has the following entity data: {Slot: 0b, ForgeCaps: {Parent: {Energy: 200}}, id: "mymod:teleport_staff", Count: 1b}

There is an nbt tag called "ForgeCaps". With that name, I assume that's where caps are saved. It increases by 100 whenever I use the staff, and it is reset to 0 whenever I reload the game