Function sigmoid_blend 

pub fn sigmoid_blend(
    gpu: &dyn GpuBackend,
    kernel: KernelHandle,
    output: DevicePtr,
    src: DevicePtr,
    sigmoid_gate: f32,
    num_elements: u32,
    stream: u64,
) -> Result<()>

2026-09-25: In-place BF16 output[i] += sigmoid_gate * src[i], where sigmoid_gate is a host value the caller has already passed through the sigmoid. The arguments are those of kernel bf16_sigmoid_blend; nothing in the tree calls this function.