Spear & new-item model/render glitch (edges broken, invisible parts)

Description:
In the Java snapshot (25w43a) of Minecraft, when holding the new “Spear” item, its edges become visually broken/glitched. The backside of the item becomes visible in an unintended way, parts of the model turn invisible or missing. Additionally, some newly added items or blocks (for example the grass block in inventory) appear with missing or corrupted parts in their model. This appears to be a rendering or model issue with these newly-added items.
Steps to reproduce:

1. Enable snapshot 25w43a in Minecraft Java Edition.

2. Obtain or craft the Spear (or acquire one in inventory).

3. Equip/hold the Spear item in hand.

4. Observe the edges/texture/model: the outlines/edges look broken, back becomes visible, some parts invisible.

5. Also check the inventory model of some new items/blocks (e.g., grass block) and verify missing parts or corruption.
   Expected result:
   New items/blocks render correctly without missing parts or broken edges. The Spear model should look consistent and edges intact.
   Actual result:
   The Spear model shows broken/glitched edges, back part visible unexpectedly, invisible / missing model parts. Some blocks/items also have model corruption in inventory.