Function reshape_and_cache_flash_v_only 

pub fn reshape_and_cache_flash_v_only(
    gpu: &dyn GpuBackend,
    kernel: KernelHandle,
    value: DevicePtr,
    v_cache: DevicePtr,
    slot_mapping: DevicePtr,
    num_tokens: u32,
    num_kv_heads: u32,
    head_dim: u32,
    block_size: u32,
    value_stride: u32,
    stream: u64,
) -> Result<()>

2026-09-25: Copy only V into the paged BF16 cache (kernel reshape_and_cache_flash_v_only), for callers whose K is written by a fused_k_norm_rope_cache_write_* launch; a reshape_and_cache there would overwrite that K.