[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/stf/graph/graph_composition.cu

@@ -0,0 +1,117 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of CUDASTF 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) 2022-2024 NVIDIA CORPORATION & AFFILIATES.
+//
+//===----------------------------------------------------------------------===//
+
+/**
+ * @file
+ * @brief Generate a library call from nested CUDA graphs generated using algorithms
+ */
+
+#include <cuda/experimental/stf.cuh>
+
+using namespace cuda::experimental::stf;
+
+// Some fake library doing MATH
+void libMATH(graph_ctx ctx, logical_data<slice<double>> x, logical_data<slice<double>> y)
+{
+  // We only want to have kernels with 4 CTAs to stress the system
+  auto spec = par<4>(par<128>());
+  ctx.launch(spec, exec_place::current_device(), x.read(), y.write()).set_symbol("MATH1")->*
+    [] __device__(auto t, auto x, auto y) {
+      for (auto i : t.apply_partition(shape(x)))
+      {
+        y(i) = cos(cos(x(i)));
+      }
+    };
+
+  ctx.launch(spec, exec_place::current_device(), x.write(), y.read()).set_symbol("MATH2")->*
+    [] __device__(auto t, auto x, auto y) {
+      for (auto i : t.apply_partition(shape(x)))
+      {
+        x(i) = sin(sin(y(i)));
+      };
+    };
+}
+
+template <typename context_t>
+void libMATH_AS_GRAPH(context_t& ctx, logical_data<slice<double>> x, logical_data<slice<double>> y)
+{
+  static algorithm alg;
+  alg.run_as_task(libMATH, ctx, x.rw(), y.write());
+}
+
+// Some fake lib doing a SWAP
+template <typename context_t>
+void libSWAP(context_t& ctx, logical_data<slice<double>> x, logical_data<slice<double>> y)
+{
+  // We only want to have kernels with 4 CTAs to stress the system
+  auto spec = par<4>(par<128>());
+  ctx.launch(spec, exec_place::current_device(), x.rw(), y.rw()).set_symbol("SWAP")->*
+    [] __device__(auto t, auto x, auto y) {
+      for (auto i : t.apply_partition(shape(x)))
+      {
+        auto tmp = x(i);
+        x(i)     = y(i);
+        y(i)     = tmp;
+      }
+    };
+}
+
+template <typename context_t>
+logical_data<slice<double>> libCOPY(context_t& ctx, logical_data<slice<double>> x)
+{
+  logical_data<slice<double>> res = ctx.logical_data(x.shape());
+
+  // We only want to have kernels with 4 CTAs to stress the system
+  auto spec = par<4>(par<128>());
+  ctx.launch(spec, exec_place::current_device(), x.read(), res.write()).set_symbol("SWAP")->*
+    [] __device__(auto t, auto x, auto res) {
+      for (auto i : t.apply_partition(shape(x)))
+      {
+        res(i) = x(i);
+      }
+    };
+
+  return res;
+}
+
+int main()
+{
+  nvtx_range r("run");
+
+  stream_ctx ctx;
+
+  const size_t N = 256 * 1024;
+  const size_t K = 8;
+
+  logical_data<slice<double>> lX[K];
+  logical_data<slice<double>> lY[K];
+
+  for (size_t i = 0; i < K; i++)
+  {
+    lX[i] = ctx.logical_data<double>(N);
+    lY[i] = ctx.logical_data<double>(N);
+
+    ctx.parallel_for(lX[i].shape(), lX[i].write(), lY[i].write()).set_symbol("INIT")->*
+      [] __device__(size_t i, auto x, auto y) {
+        x(i) = 2.0 * i + 12.0;
+        y(i) = -3.0 * i + 17.0;
+      };
+  }
+
+  for (size_t i = 0; i < K; i++)
+  {
+    auto tmp = libCOPY(ctx, lX[i]);
+    libSWAP(ctx, tmp, lY[i]);
+    libMATH_AS_GRAPH(ctx, lX[i], lY[i]);
+    libSWAP(ctx, lX[i], lY[i]);
+  }
+
+  ctx.finalize();
+}