First‑person main‑hand overlay renders incorrectly on slim skin;offhand works fine,NOT MC‑273800

Description

When using a double-layer slim (Alex 3px arm) skin with overlay texture:

1. The player model is confirmed as Slim/Alex, NOT Classic Steve.

2. In first-person view:

◦ Main hand (default right hand): The overlay sleeve texture makes the arm look thicker/wider visually.

◦ Offhand (left hand): Renders correctly, the arm stays slim, matches expected Alex appearance.

1. Press F5 for third-person view: Both arms look identical and normal slim Alex. No visual difference between left and right arms.

2. If I swap main hand to left in settings: the visual "wider" effect moves to new main hand, offhand returns to normal.

3. This bug is NOT MC-273800. The underlying arm geometry remains Slim/Alex all the time; it is not incorrectly loaded as Steve classic 4px arm.

4. The issue only appears in first-person rendering of the outer overlay layer of the arm. Base layer renders correctly.

Expected behavior:
The overlay layer on main hand and offhand should render identically. Main hand should have the same visual width as offhand for slim Alex skin.

Steps to reproduce:

1. Create Slim(Alex) skin with painted overlay sleeve on arms in Blockbench.

2. Upload skin via official http://Minecraft.net webpage.

3. Enter game, first-person view, observe main hand vs offhand.

4. Toggle main hand option, confirm visual artifact follows main hand.

5. Switch to third-person(F5), arms are both normal.

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