Colossal Chests 2: refuse chest cores carrying items in chests

[rubensworks]

A chest core that holds items keeps them on its item when it is mined. Storing such a core in another chest nests the contents, and repeating that grows saved data without limit until the NBT overflows. This PR makes chests refuse those items.

Summary

• What is refused: any item carrying a core's contents (the colossalchests2:chest_contents item component), and any item holding one inside vanilla containers: shulker boxes (minecraft:container) and bundles (minecraft:bundle_contents), at any depth. That closes the indirect route of a core in a shulker box in a chest.
• Where: in ChestStorage.canAccept, which every insert path goes through (GUI clicks and shift-clicks, hoppers and other automation, the Display wall, the item handler's isItemValid; the Magnet wall in Colossal Chests 2, Phase 7: Magnet wall #226 inserts the same way), and in lockTo, since a locked slot stores its type with all components too.
• Still allowed: empty cores, cores without contents (e.g. with only upgrades), and shulker boxes or bundles with other items.
• Depth cap: items nested more than 8 containers deep are refused outright, so a crafted stack can't make the check itself expensive. Vanilla play never gets near that.
• Detection by component id: the check compares the component's registry id instead of using the registered holder, so it also works where the mod's registries aren't loaded, such as unit tests. A game test asserts the id matches the real component.

Design notes

• I did not stop filled cores from going into shulker boxes. Vanilla's hook for that (Item#canFitInsideContainerItems) applies to every stack of an item, so it would also forbid empty cores, and Fabric has no per-stack variant. Refusing on our side covers the recursion: a core's contents can never hold a filled core, directly or through vanilla containers.
• Containers from other mods with their own item components are not inspected.

Validation

Criterion	Covered by
A real filled core (from breaking a chest with stone) is refused by insert, insertAutomated, the item handler, and lockTo; a shulker box holding it and a bundle holding that shulker box are refused; an empty core and a shulker box with stone are accepted; the component id matches	Game test testFilledCoresCanNotBeStored
Plain items and vanilla containers are allowed, nesting deeper than 8 is refused	Unit tests TestNestedChests (3)

Totals: 293 unit tests; game tests Fabric 74, Forge 72, NeoForge 72, all passing.

In-game (clientdevbridge): script in clientdevbridge-screenshots/nested-cores. On NeoForge, a core carrying 100 stone (from breaking a real chest), a shulker box holding it, and a shulker box holding stone were shift-clicked into another chest. Read back from the world: only the stone shulker box was stored; the other two stayed in the inventory. No screenshots, as the result is in the state.

Known issues

• No feedback: a refused shift-click silently does nothing, like any item the chest can't take. A tooltip line on filled cores could explain it; I'd do that with the Phase 9 tooltips.

🤖 Generated with Claude Code

https://claude.ai/code/session_01RSz5r6eowhjNuANBjZE2v6