ArrayIndexOutOfBoundsException in Sodium's LevelSlice.getBlockState, triggered via Continuity's StandardOverlayQuadProcessor.getEmitter — possible bit-shift bug with negative section Y

[Marcy-02]

Environment

• Minecraft 1.21.1, NeoForge 21.1.248
• Sodium 0.8.12+mc1.21.1
• Continuity 3.0.0+1.21.neoforge
• Iris 1.8.14-beta.1

I've hit this crash three times so far, always during chunk mesh building, always on minecraft:deepslate level.

Possible pattern in the corrupted index (unconfirmed, just a hypothesis)
The three crashes I've collected all produced indices that look like clean multiples of 2^21 (2097152) plus a small remainder that would otherwise be a valid array index (0–26, since the LevelSlice cache is a 3×3×3 = 27 array):

Crash	Index	≈ Fit
1	-2097139	-(1 × 2^21) + 13
2	-2097140	-(1 × 2^21) + 12
3	-6291443	-(3 × 2^21) + 13

I don't know exacly what this means but it seems like during the neighbor serch a cordinate is being shifted by 21 bits. Since section Y can be negative near bedrock/deep-slate layers, that could produce these large negative indices instead I want to stress this is just a hypothesis from pattern-matching three data points.

Repro conditions (best guess)

• Happens specifically while rendering deepslate sections
• All three crashes were around y=-64 to y=-17

crash-2026-08-27_13.52.03-client.txt
crash-2026-08-27_19.12.40-client.txt
crash-2026-08-27_19.20.09-client.txt