The bug

If a chest with a custom name or other important component data is equipped on a donkey, mule or llama, and then said donkey, mule or llama dies, a normal chest will be dropped with none of the properties of the chest that was actually equipped.

This issue also affected saddles until 25w03a, in which this problem was fixed. It still affecting chests is a bad thing.

How to reproduce

1. Give a chest a name
2. Equip it on a donkey
3. Kill the donkey

Expected results

When you get the chest back, it has a name.

Actual results

This chest has no name.

How to fix

Make chests classified as a type of "equipment": instead of toggling a boolean, using a chest on one of these animals would place the chest item in an invisible "chest slot". This way, when the animal dies, instead of dropping "a chest" it drops the item in its chest slot, complete with all its associated data.

This would also fix the issues MC-224886, MC-279508 and MC-279564.