feat(cccl): integrate missing CCCL directories — python/, ci/, .agent/, docs/, test/

Sparse-checkout from NVIDIA/cccl main branch to complete cccl_upstream:

Added:
- python/cuda_cccl/ (226 files) — Python bindings for device-level algorithms
  Critical for muh toolchain: cuda.compute.reduce_into, scan, radix_sort, etc.
  Includes 204 .py files with full test coverage for all 27 algorithms
- ci/ (163 files) — Build/test infrastructure
  build_cub.sh, test_cub.sh, build_and_test_targets.sh, matrix.yaml
  Directly maps to our [INFRA-CI] and [INFRA-BUILD] items
- .agent/skills/ (7 files) — NVIDIA's own agent skills for CCCL
  cccl-style/SKILL.md, cccl-test/SKILL.md, sass-diff/SKILL.md
- docs/ (491 files) — Official CCCL documentation
  CI references, CMake guides, Python compute docs, libcudacxx PTX docs
- test/ (12 files) — Top-level integration tests (cuda_smoke, stdpar)
- Root configs: .clang-format, .clang-tidy, CONTRIBUTING.md, pyproject.toml
- CLAUDE.md symlink → AGENTS.md (NVIDIA's standard)

cccl_upstream now mirrors full NVIDIA/cccl structure:
  Before: 42M (cub + thrust + libcudacxx + cudax + c + examples + benchmarks)
  After:  53M (+python +ci +docs +.agent +test +configs)

This completes the CCCL base needed for:
- [muh-bench] items: ci/util/build_and_test_targets.sh for targeted builds
- [CCCL-verify] items: python/cuda_cccl/tests/ as reference implementations
- [CCCL-test] items: ci/test_cub.sh, ci/test_thrust.sh
- Agent workflow: .agent/skills/ for consistent style and test patterns

cccl_upstream/python/cuda_cccl/cuda/cccl/__init__.py

@@ -0,0 +1,27 @@
+"""
+CUDA Core Library (CCCL) Python Package
+"""
+
+import importlib.metadata
+
+try:
+    __version__ = importlib.metadata.version("cuda-cccl")
+except Exception:
+    __version__ = "0.0.0"
+
+from .headers.include_paths import get_include_paths
+
+# cuda.bindings is required, but instead of being listed as a required dependency,
+# it is installed via an extra (e.g., [cu12] or [cu13]).
+#
+# One of the first things we should do is check that it is available, and raise
+# a helpful error message if it is not.
+try:
+    import cuda.bindings as _cuda_bindings  # type: ignore
+except ImportError:
+    raise ImportError(
+        "cuda.bindings is not installed. Please install the appropriate extra cuda-cccl[cu12] or cuda-cccl[cu13]."
+    ) from None
+del _cuda_bindings
+
+__all__ = ["get_include_paths", "__version__"]

cccl_upstream/python/cuda_cccl/cuda/cccl/_cuda_version_utils.py

@@ -0,0 +1,24 @@
+# Copyright (c) 2025, NVIDIA CORPORATION & AFFILIATES. ALL RIGHTS RESERVED.
+#
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+"""
+CUDA version detection utilities shared across the cccl package.
+"""
+
+from typing import Optional
+
+import cuda.bindings
+
+
+def detect_cuda_version() -> Optional[int]:
+    cuda_version = cuda.bindings.__version__
+    return int(cuda_version.split(".")[0])
+
+
+def get_recommended_extra(cuda_version: Optional[int]) -> str:
+    """Get the recommended pip extra for the detected CUDA version."""
+    if cuda_version == 13:
+        return "cu13"
+    else:
+        return "cu12"

cccl_upstream/python/cuda_cccl/cuda/cccl/headers/__init__.py

@@ -0,0 +1,7 @@
+# Copyright (c) 2025, NVIDIA CORPORATION & AFFILIATES. ALL RIGHTS RESERVED.
+#
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+from .include_paths import get_include_paths
+
+__all__ = ["__version__", "get_include_paths"]

cccl_upstream/python/cuda_cccl/cuda/cccl/headers/include/__init__.py

@@ -0,0 +1 @@
+# Intentionally empty

cccl_upstream/python/cuda_cccl/cuda/cccl/headers/include_paths.py

@@ -0,0 +1,51 @@
+# Copyright (c) 2025, NVIDIA CORPORATION & AFFILIATES. ALL RIGHTS RESERVED.
+#
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+import sys
+from dataclasses import dataclass
+from functools import lru_cache
+from importlib.resources import as_file, files
+from pathlib import Path
+from typing import Optional
+
+# type: ignore[import-not-found]
+from cuda.pathfinder import find_nvidia_header_directory
+
+
+@dataclass
+class IncludePaths:
+    cuda: Optional[Path]
+    libcudacxx: Optional[Path]
+    cub: Optional[Path]
+    thrust: Optional[Path]
+
+    def as_tuple(self):
+        # Note: higher-level ... lower-level order:
+        return (self.thrust, self.cub, self.libcudacxx, self.cuda)
+
+
+@lru_cache()
+def get_include_paths(probe_file: str = "cub/version.cuh") -> IncludePaths:
+    cuda_incl = find_nvidia_header_directory("cudart")
+    if cuda_incl is None:
+        raise RuntimeError("Unable to locate CUDA include directory.")
+
+    with as_file(files("cuda.cccl.headers.include")) as f:
+        cccl_incl = Path(f)
+
+    probe_file_path = Path(probe_file)
+    if not (cccl_incl / probe_file_path).exists():
+        for sp in sys.path:
+            cccl_incl = Path(sp).resolve() / "cuda" / "cccl" / "headers" / "include"
+            if (cccl_incl / probe_file_path).exists():
+                break
+        else:
+            raise RuntimeError("Unable to locate CCCL include directory.")
+
+    return IncludePaths(
+        cuda=cuda_incl,
+        libcudacxx=cccl_incl,
+        cub=cccl_incl,
+        thrust=cccl_incl,
+    )

cccl_upstream/python/cuda_cccl/cuda/cccl/parallel/__init__.py

@@ -0,0 +1,9 @@
+# Copyright (c) 2024, NVIDIA CORPORATION & AFFILIATES. ALL RIGHTS RESERVED.
+#
+# SPDX-License  -Identifier: Apache-2.0 WITH LLVM-exception
+
+from . import experimental
+
+__all__ = [
+    "experimental",
+]

cccl_upstream/python/cuda_cccl/cuda/cccl/parallel/experimental/__init__.py

@@ -0,0 +1,24 @@
+# Copyright (c) 2025, NVIDIA CORPORATION.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# alias for backwards compatibility
+
+from warnings import warn
+
+from cuda.compute import *  # noqa: F403
+
+warn(
+    "The module cuda.cccl.parallel.experimental is deprecated. Use cuda.compute instead.",
+    FutureWarning,
+)