[Bug] `namespace "std" has no member "copy_n"` in include/common/util.cuh when building kernels/attention/mha_h100

[ShlokVFX]

Environment

• GPU: NVIDIA H100
• CUDA: 12.8 (via PyTorch/Lightning AI Cloudspace)
• PyTorch: bundled via Lightning AI Cloudspace
• Build command: make from kernels/attention/mha_h100

Bug Description

Building kernels/attention/mha_h100 fails with two errors in
ThunderKittens/include/common/util.cuh:

/teamspace/studios/this_studio/ThunderKittens/include/common/util.cuh(503): 
error: namespace "std" has no member "copy_n"
        std::copy_n(other.attributes, num_attributes, attributes);

/teamspace/studios/this_studio/ThunderKittens/include/common/util.cuh(509): 
error: namespace "std" has no member "copy_n"
        std::copy_n(other.attributes, num_attributes, attributes);

2 errors detected in the compilation of "mha_h100.cu".
make: *** [../../common.mk:121: _C.cpython-312-x86_64-linux-gnu.so] Error 2

Root Cause

std::copy_n is defined in <algorithm>, but that header is not included
in util.cuh. In some environments (e.g. PyTorch + CUDA toolkit combos),
<algorithm> is not pulled in transitively, causing the build to fail.

Note: A similar class of issue was reported in #40 and #45
(std::bit_cast missing in base_types.cuh), but this is a separate
occurrence in util.cuh.

Fix

Adding #include <algorithm> at the top of
ThunderKittens/include/common/util.cuh resolves the error:

+ #include <algorithm>

Result After Fix

Build succeeds with warnings only (harmless #191-D type qualifier warnings
and #177-D unused variable warning). The kernel runs successfully:

Suggested Fix (one-liner)

sed -i '1s/^/#include <algorithm>\n/' \
  ThunderKittens/include/common/util.cuh

Or manually add #include <algorithm> at the top of util.cuh.