[CCCL] Add missing CCCL components: c2h, nvbench_helper, cmake, cudax, AGENTS.md

Added 863 files from NVIDIA/cccl sparse checkout:
- c2h/ (27 files): Catch2 test helpers — generators, validators, runner
- nvbench_helper/ (10 files): Benchmark harness utilities
- cmake/ (29 files): CMake presets and build helpers
- cudax/ (794 files): Experimental CUDA extensions
- AGENTS.md: NVIDIA's official AI agent instructions for CCCL
- CMakePresets.json: Standardized build configurations
- cccl-version.json: Version tracking

Also added CCCL_ASSET_MAP.md mapping all 4295 CCCL files to
competition value and PRD items.

cccl_upstream now covers 100% of competition-critical assets:
- 27 tuning headers (SM80/90/100 benchmark data)
- 32 dispatch headers (algorithm implementations)
- 60 Thrust examples (correctness verification)
- 217 CUB Catch2 tests (regression matrix)
- 153 CUB benchmarks (parameter space search)
- 18 CUB examples (API verification)
- 27 test helpers + benchmark harness
- 794 cudax experimental extensions

cccl_upstream/cudax/test/multi_gpu/nccl/concepts.cu

@@ -0,0 +1,100 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of CUDA Experimental in CUDA C++ Core Libraries,
+// under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+// SPDX-FileCopyrightText: Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES.
+//
+//===----------------------------------------------------------------------===//
+
+#include <cuda/functional> // cuda::maximum, cuda::minimum
+#include <cuda/std/cstdint>
+#include <cuda/std/functional> // cuda::std::plus, cuda::std::multiplies
+
+#include <cuda/experimental/__nccl/nccl_api.h>
+
+#include <c2h/catch2_test_helper.h>
+
+namespace
+{
+// A trivially-copyable aggregate with no corresponding NCCL data type.
+struct trivial_aggregate
+{
+  int a;
+  double b;
+};
+
+// A non-trivially-copyable type (user-provided copy ctor).
+struct non_trivial
+{
+  non_trivial(const non_trivial&) {} // NOLINT(modernize-use-equals-default)
+  int a;
+};
+} // namespace
+
+C2H_TEST("nccl type and reduction-op traits", "[multi_gpu][nccl]")
+{
+  namespace nccl = ::cuda::experimental::__nccl;
+
+  // --- __has_nccl_type_of -------------------------------------------------------
+  //
+  // True only for the fixed set of types __nccl_type_of() recognizes.
+  STATIC_REQUIRE(nccl::__has_nccl_type_of<::cuda::std::int8_t>);
+  STATIC_REQUIRE(nccl::__has_nccl_type_of<::cuda::std::uint8_t>);
+  STATIC_REQUIRE(nccl::__has_nccl_type_of<::cuda::std::int32_t>);
+  STATIC_REQUIRE(nccl::__has_nccl_type_of<::cuda::std::uint32_t>);
+  STATIC_REQUIRE(nccl::__has_nccl_type_of<::cuda::std::int64_t>);
+  STATIC_REQUIRE(nccl::__has_nccl_type_of<::cuda::std::uint64_t>);
+  STATIC_REQUIRE(nccl::__has_nccl_type_of<float>);
+  STATIC_REQUIRE(nccl::__has_nccl_type_of<double>);
+  STATIC_REQUIRE(nccl::__has_nccl_type_of<bool>);
+
+  // cv-qualifications are stripped via remove_cvref_t before the lookup.
+  STATIC_REQUIRE(nccl::__has_nccl_type_of<const float>);
+  STATIC_REQUIRE(nccl::__has_nccl_type_of<volatile int>);
+  STATIC_REQUIRE(nccl::__has_nccl_type_of<float&>);
+
+  // Unsupported types have no NCCL data type.
+  STATIC_REQUIRE(!nccl::__has_nccl_type_of<long double>);
+  STATIC_REQUIRE(!nccl::__has_nccl_type_of<void>);
+  STATIC_REQUIRE(!nccl::__has_nccl_type_of<int*>);
+  STATIC_REQUIRE(!nccl::__has_nccl_type_of<trivial_aggregate>);
+
+  // --- __nccl_type_of_v ---------------------------------------------------------
+  STATIC_REQUIRE(nccl::__nccl_type_of_v<bool> == nccl::__ncclChar);
+  STATIC_REQUIRE(nccl::__nccl_type_of_v<::cuda::std::int8_t> == nccl::__ncclInt8);
+  STATIC_REQUIRE(nccl::__nccl_type_of_v<::cuda::std::uint8_t> == nccl::__ncclUint8);
+  STATIC_REQUIRE(nccl::__nccl_type_of_v<::cuda::std::int32_t> == nccl::__ncclInt32);
+  STATIC_REQUIRE(nccl::__nccl_type_of_v<::cuda::std::uint32_t> == nccl::__ncclUint32);
+  STATIC_REQUIRE(nccl::__nccl_type_of_v<::cuda::std::int64_t> == nccl::__ncclInt64);
+  STATIC_REQUIRE(nccl::__nccl_type_of_v<::cuda::std::uint64_t> == nccl::__ncclUint64);
+  STATIC_REQUIRE(nccl::__nccl_type_of_v<float> == nccl::__ncclFloat);
+  STATIC_REQUIRE(nccl::__nccl_type_of_v<double> == nccl::__ncclDouble);
+
+  // cv-ref qualifiers are removed before mapping.
+  STATIC_REQUIRE(nccl::__nccl_type_of_v<const double&> == nccl::__ncclDouble);
+
+  // --- __nccl_redop_of_v --------------------------------------------------------
+  STATIC_REQUIRE(nccl::__nccl_redop_of_v<::cuda::std::plus<>> == nccl::__ncclSum);
+  STATIC_REQUIRE(nccl::__nccl_redop_of_v<::cuda::std::multiplies<>> == nccl::__ncclProd);
+  STATIC_REQUIRE(nccl::__nccl_redop_of_v<::cuda::maximum<>> == nccl::__ncclMax);
+  STATIC_REQUIRE(nccl::__nccl_redop_of_v<::cuda::minimum<>> == nccl::__ncclMin);
+  STATIC_REQUIRE(nccl::__nccl_redop_of_v<const ::cuda::std::plus<int>&> == nccl::__ncclSum);
+
+  // --- __has_nccl_redop ---------------------------------------------------------
+  STATIC_REQUIRE(nccl::__has_nccl_redop_of<::cuda::std::plus<>>);
+  STATIC_REQUIRE(nccl::__has_nccl_redop_of<::cuda::std::multiplies<>>);
+  STATIC_REQUIRE(nccl::__has_nccl_redop_of<::cuda::maximum<>>);
+  STATIC_REQUIRE(nccl::__has_nccl_redop_of<::cuda::minimum<>>);
+
+  // Typed specializations are recognized too.
+  STATIC_REQUIRE(nccl::__has_nccl_redop_of<::cuda::std::plus<int>>);
+
+  // cv-ref qualifiers are stripped before the lookup.
+  STATIC_REQUIRE(nccl::__has_nccl_redop_of<const ::cuda::std::plus<>&>);
+
+  // Unsupported functors and non-functor types are rejected.
+  STATIC_REQUIRE(!nccl::__has_nccl_redop_of<::cuda::std::minus<>>);
+  STATIC_REQUIRE(!nccl::__has_nccl_redop_of<int>);
+}