fix: Gemma 4 + TurboQuant KV no longer crashes on second prompt when --cache-reuse enabled#10
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Ooooze merged 1 commit intoMay 12, 2026
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…--cache-reuse enabled TurboQuant (turbo2/3/4) uses kernel-level WHT rotation which is position-invariant -- WHT preserves inner products so no RoPE correction is needed after a KV position shift. build_graph_shift() assumed standard quantized tensors with upstream rotation, but TurboQuant sets attn_rot_k=0 and handles rotation at kernel level. Building the shift graph with turbo-padded tensors causes a null buffer assert and segfault on the second prompt. Fix: skip build_graph_shift() layers and get_has_shift() entirely for turbo KV types. Position tracking via seq_add() still works correctly -- only the broken RoPE re-rotation kernel is skipped.
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AtomicBot-ai:feature/turboquant-kv-cache
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Overview
The previous cache bug #9 prevented the discovery of a knock on problem in the RoPE implementation. This fix is necessary to allow TurboQuant to function properly with cache reuse with gemma 4.
TurboQuant (turbo2/3/4) uses kernel-level WHT rotation, which is position-invariant -- WHT preserves inner products so no RoPE correction is needed after a KV position shift.
build_graph_shift() assumed standard quantized tensors with upstream rotation, but TurboQuant sets attn_rot_k=0 and handles rotation at kernel level. Building the shift graph with turbo-padded tensors causes a null buffer assert and segfault on the second prompt.
Fix: skip build_graph_shift() layers and get_has_shift() entirely for turbo KV types. Position tracking via seq_add() still works correctly -- only the broken RoPE re-rotation kernel is skipped.
Additional information
Combined with the previous PR that recognises caching in Gemma 4 this leads to near instataneous chat conversations on llama-sever web gui, when previously there was a reprocessing lag of 7 seconds plus, and a crash with any prompt causing a sliding window shift.
I have tested to around 6k of available 250k context and working flawlessly now.
Requirements