[INFRA] Import NVIDIA/CCCL upstream as optimization reference library

CCCL (CUDA C++ Core Libraries) provides:
- CUB: device/block/warp-level GPU primitives (reduce, scan, sort, topk)
- Thrust: high-level parallel algorithms (transform_reduce, sort, scan)
- libcudacxx: CUDA C++ standard library (atomics, barriers, memory)
- cudax: experimental features (memory resources, allocators)
- Tuning policies: per-SM hardware-specific algorithm parameters

Competition optimization vectors mapped to CCCL:
- Output TPS (83% weight): warp_reduce, block_reduce, device_topk
- Input TPS (14% weight): device_scan, block_load, prefetch
- Cache TPS (3% weight): prefix caching strategy patterns
- Memory (0.9 util): pooled/cached/buddy allocators

Source: https://github.com/NVIDIA/cccl (shallow clone, HEAD only)
License: Apache-2.0

cccl_upstream/c/experimental/stf/test/test_ctx.cpp

@@ -0,0 +1,92 @@
+//===----------------------------------------------------------------------===//
+//
+// 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) 2025 NVIDIA CORPORATION & AFFILIATES.
+//
+//===----------------------------------------------------------------------===//
+
+#include <cuda_runtime.h>
+
+#include <c2h/catch2_test_helper.h>
+#include <cccl/c/experimental/stf/stf.h>
+
+C2H_TEST("basic stf context", "[context]")
+{
+  stf_ctx_handle ctx = stf_ctx_create();
+  REQUIRE(ctx != nullptr);
+  stf_ctx_finalize(ctx);
+}
+
+C2H_TEST("stf_ctx_wait reads data without finalizing", "[context]")
+{
+  stf_ctx_handle ctx = stf_ctx_create();
+  REQUIRE(ctx != nullptr);
+
+  int h_value                  = 0;
+  stf_logical_data_handle lVal = stf_logical_data(ctx, &h_value, sizeof(int));
+  REQUIRE(lVal != nullptr);
+  stf_logical_data_set_symbol(lVal, "val");
+
+  int src_val = 42;
+
+  stf_host_launch_handle h = stf_host_launch_create(ctx);
+  REQUIRE(h != nullptr);
+  stf_host_launch_set_symbol(h, "set42");
+  stf_host_launch_add_dep(h, lVal, STF_WRITE);
+  stf_host_launch_set_user_data(h, &src_val, sizeof(int), nullptr);
+  stf_host_launch_submit(h, [](stf_host_launch_deps_handle deps) {
+    int* data = (int*) stf_host_launch_deps_get(deps, 0);
+    int* src  = (int*) stf_host_launch_deps_get_user_data(deps);
+    data[0]   = *src;
+  });
+  stf_host_launch_destroy(h);
+
+  int result = 0;
+  int rc     = stf_ctx_wait(ctx, lVal, &result, sizeof(int));
+  REQUIRE(rc == 0);
+  REQUIRE(result == 42);
+
+  // The context remains usable after waiting.
+  src_val = 99;
+
+  stf_host_launch_handle h2 = stf_host_launch_create(ctx);
+  REQUIRE(h2 != nullptr);
+  stf_host_launch_set_symbol(h2, "set99");
+  stf_host_launch_add_dep(h2, lVal, STF_WRITE);
+  stf_host_launch_set_user_data(h2, &src_val, sizeof(int), nullptr);
+  stf_host_launch_submit(h2, [](stf_host_launch_deps_handle deps) {
+    int* data = (int*) stf_host_launch_deps_get(deps, 0);
+    int* src  = (int*) stf_host_launch_deps_get_user_data(deps);
+    data[0]   = *src;
+  });
+  stf_host_launch_destroy(h2);
+
+  result = 0;
+  rc     = stf_ctx_wait(ctx, lVal, &result, sizeof(int));
+  REQUIRE(rc == 0);
+  REQUIRE(result == 99);
+
+  stf_logical_data_destroy(lVal);
+  stf_ctx_finalize(ctx);
+}
+
+C2H_TEST("stf_ctx_wait rejects invalid arguments", "[context]")
+{
+  stf_ctx_handle ctx = stf_ctx_create();
+  REQUIRE(ctx != nullptr);
+
+  int h_value                  = 0;
+  stf_logical_data_handle lVal = stf_logical_data(ctx, &h_value, sizeof(int));
+  REQUIRE(lVal != nullptr);
+
+  int result = 0;
+  REQUIRE(stf_ctx_wait(nullptr, lVal, &result, sizeof(int)) != 0);
+  REQUIRE(stf_ctx_wait(ctx, nullptr, &result, sizeof(int)) != 0);
+  REQUIRE(stf_ctx_wait(ctx, lVal, nullptr, sizeof(int)) != 0);
+
+  stf_logical_data_destroy(lVal);
+  stf_ctx_finalize(ctx);
+}