Function plan_dispatch_1d 

pub fn plan_dispatch_1d(
    limits: &Limits,
    total_threads: u64,
    workgroup_x: u32,
) -> Result<(DispatchGrid, u32), String>

Plan a 1-D dispatch covering total_threads items with workgroup_x threads each, automatically folding into a 2-D grid when the required workgroup count would exceed the per-axis limit.

The companion shader must decode its linear slot as wgid.y * grid_x + wgid.x (exactly as crate::shader::reduction_nd_wgsl does) and early-return when the slot is out of range.

grid_x (the second return value) is the fold width to embed as the grid_x uniform; for a non-folded dispatch it equals the X workgroup count and the decode is still correct (wgid.y == 0).

Returns an error string if total_threads is so large that even a square 2-D grid would exceed the per-axis cap on both axes.