Nested Shulkers

# Nested Shulkers

Vanilla Minecraft refuses to let a shulker box go inside another shulker box. This mod removes
that restriction.

## What it does

- **Nest boxes in the GUI** — drag or shift-click a shulker box straight into an open one
- **Works with automation** — hoppers, droppers and other item transport can insert them too
- **Nothing else changes** — only shulker box stacks are affected; every other item still follows
  the vanilla insertion rules
- **Bundles are untouched** — they still reject shulker boxes, exactly like vanilla

Vanilla blocks nesting in two separate places, and both are lifted. Mods that only patch the
inventory check leave hoppers still refusing the item; this one handles both paths.

## Nesting depth limit

Nesting is capped at **5 levels deep** (a plain box is level 1, a box holding a box is level 2,
and so on).

This isn't arbitrary caution. A shulker box carries its contents in the item's data, so every
level of nesting multiplies the data attached to a single item stack. Left unbounded, a
sufficiently nested box produces a stack too large to send over the network — which kicks players
off the server and can damage the chunk the box is sitting in. Five levels is already **531,441
stacks** of storage inside one box, which is more than any survival world will ever need.

The cap is currently a constant in the source rather than a config file. If you want a different
value, change `MAX_NESTING_DEPTH` in `NestedShulkers.java` and rebuild. A proper config file is
planned.

## Installation

1. Install **Fabric Loader 0.16.0 or newer** for Minecraft 1.21.1
2. Drop the jar into your `mods` folder

**Fabric API is not required.**

## Multiplayer

Install it on **both the server and the client**. The server decides what may be inserted, but the
client predicts inventory clicks locally — with the mod on the server only, the box will appear to
reject the item and snap back before the server corrects it.

## Compatibility

The mod applies two small Mixins that run at the very start of the vanilla checks and return early
only for shulker boxes. It doesn't overwrite any method outright, so it should sit alongside most
other mods without trouble. The likely exception is another mod that changes the same two shulker
box insertion checks.

## License

MIT.