Iron Backpacks (Unofficial Port)

Iron Backpacks 1.0.3 for Minecraft 26.3, NeoForge and Fabric: the first version for Minecraft 26.3 (needs Java 25). An unofficial port of Iron Backpacks 3.0.8 by gr8pefish (GPL-3.0).

Install: drop the jar for your loader into the mods folder of the server and of every client; JEI is optional.

What's new

• Minecraft 26.3. The same backpacks, upgrades, recipes, GUI and translations as the 1.21.1 version. Item models now use client item definitions, and the JEI "Increase Backpack Tier" category gets its recipes from the server (26.x clients have none otherwise).
• Worlds from 1.21.1 are not converted by this mod; Minecraft's own world upgrade applies.

Fixes of the original mod's bugs

• No more item duplication through an open backpack (original issues #234, #268). The backpack GUI stayed open after its backpack was dropped (for example the drop key pressed together with the open key) or pulled out by another mod, so its slots could be emptied while the dropped backpack still held the items. Now the GUI closes as soon as that backpack leaves the player, and clicks after that do nothing.
• Contents are no longer lost or reverted by inventory sorters (#255, #221). The contents were written only when the GUI closed, into the backpack that was opened; a sorter that moved or replaced it while the GUI was open left the new copy with the old contents. Every change is now saved into the backpack at once.
• The open key respects the Latch upgrade. It opened anyone's latched backpack in your inventory (only a right click checked the owner).
• The open key plays the opening sound (#243).

Tested

• 20 in-game tests (GameTests) on NeoForge 26.3.0.94 and on Fabric (Fabric API 0.164.0), also with the Fabric release jar on a real Fabric server.
• The scripted client scene on both loaders: every backpack, its GUI, dyed backpacks, tooltips, the anvil, the creative tab and JEI 31.16.
• Performance against shulker boxes: 36 full backpacks in the open inventory keep 92 % of the frame rate of 36 full shulker boxes; the server tick is the same.

Known: the default open key (I) is also the key of the debug combination F3+I in 26.x; they don't interfere.

Report bugs of this port here, not to the original author. Every difference from 1.12.2: PORTLOG.md.