CraftAbstractInventoryView returns wrong Slot number in Crafter views

[codeHusky]

Like the Crafting Table, the Crafter menu uses different ID ordering than normal over the network. Unlike the Crafting table, the Crafter is weird.
https://minecraft.wiki/w/Java_Edition_protocol/Inventory#Crafter

Exact test conditions are checking getClickedInventory() instanceOf PlayerInventory, e.getClick().isRightClick(), as well as getCursor().getType() == Material.AIR, though I don't believe those are important.

The following code will fail with the current implementation, placing the item in the wrong place during an InventoryClickEvent.

InventoryClickEvent event; // example
// ... 
event.getInventory().setItem(event.getSlot(), new ItemStack(Material.DIAMOND));
// OR
event.setCurrentItem(new ItemStack(Material.DIAMOND));

Verified issue against aa4ef06 (1.21.8) but probably affects versions since Crafter was introduced

This server is running Paper version 1.21.8-4-main@aa4ef06 (2025-07-17T23:33:28Z) (Implementing API version 1.21.8-R0.1-SNAPSHOT)
You are running the latest version

[codeHusky]

I've implemented a fix for this on my own Folia fork that may be useful in resolving it properly long term on Paper
https://github.com/CallMeCarsub/Folia/blob/b22bc84294a3dcdbbbceefca58993ceeca732ba0/folia-server/paper-patches/features/0010-Fix-crafter-slots.patch

// The Crafter's result slot is indexed at the end rather than in first 10 slots
if(this.getType() == InventoryType.CRAFTER){
    if(slot == 45){
        // return the relevant slot (? untested)
        return 9;
    }
    slot += 5;
}