Move CodSpeed library setup to Python script

Extract inline shell from CI workflow into script/setup_codspeed_lib.py.
Pins codspeed-cpp to a specific commit SHA for reproducibility.

.github/workflows/ci.yml

@@ -327,37 +327,12 @@ jobs:
           python-version: ${{ env.DEFAULT_PYTHON }}
           cache-key: ${{ needs.common.outputs.cache-key }}
 
-      - name: Set up CodSpeed benchmark library
-        # CodSpeed requires their google_benchmark fork for instrumentation.
-        # Clone and create a PlatformIO-compatible library layout.
-        run: |
-          CODSPEED_SHA=d6b4111428ae1f1667fec9bff009522378d5d347
-          git clone https://github.com/CodSpeedHQ/codspeed-cpp.git /tmp/codspeed-cpp
-          git -C /tmp/codspeed-cpp checkout "$CODSPEED_SHA"
-          # Create library.json combining google_benchmark + codspeed core
-          cat > /tmp/codspeed-cpp/google_benchmark/library.json << 'LIBJSON'
-          {
-            "name": "benchmark",
-            "version": "0.0.0",
-            "build": {
-              "flags": [
-                "-I/tmp/codspeed-cpp/core/include",
-                "-I/tmp/codspeed-cpp/core/instrument-hooks",
-                "-DHAVE_STD_REGEX",
-                "-DHAVE_STEADY_CLOCK",
-                "-DBENCHMARK_STATIC_DEFINE"
-              ],
-              "srcFilter": ["+<src/*.cc>", "+</tmp/codspeed-cpp/core/src/*.cpp>"],
-              "includeDir": "include"
-            }
-          }
-          LIBJSON
-
       - name: Build benchmarks
         id: build
         run: |
           . venv/bin/activate
-          BENCHMARK_LIB="symlink:///tmp/codspeed-cpp/google_benchmark" \
+          BENCHMARK_LIB=$(python script/setup_codspeed_lib.py)
+          BENCHMARK_LIB="$BENCHMARK_LIB" \
             script/cpp_benchmark.py --all --build-only 2>&1 | tee /tmp/bench-build.log
           BINARY=$(tail -1 /tmp/bench-build.log)
           echo "binary=$BINARY" >> $GITHUB_OUTPUT

script/setup_codspeed_lib.py

@@ -0,0 +1,93 @@
+#!/usr/bin/env python3
+"""Set up CodSpeed's google_benchmark fork as a PlatformIO library.
+
+CodSpeed requires their codspeed-cpp fork for CPU simulation instrumentation.
+This script clones the repo and creates a PlatformIO-compatible library.json
+that combines the google_benchmark and codspeed core sources.
+
+Usage:
+    python script/setup_codspeed_lib.py [--output-dir DIR]
+
+Prints the PlatformIO library path (symlink:// URL) to stdout.
+"""
+
+from __future__ import annotations
+
+import argparse
+import json
+from pathlib import Path
+import subprocess
+
+# Pin to a specific commit for reproducibility
+CODSPEED_CPP_REPO = "https://github.com/CodSpeedHQ/codspeed-cpp.git"
+CODSPEED_CPP_SHA = "d6b4111428ae1f1667fec9bff009522378d5d347"
+
+DEFAULT_OUTPUT_DIR = "/tmp/codspeed-cpp"
+
+
+def setup_codspeed_lib(output_dir: Path) -> str:
+    """Clone codspeed-cpp and create PlatformIO library layout.
+
+    Args:
+        output_dir: Directory to clone into
+
+    Returns:
+        PlatformIO library path (symlink:// URL)
+    """
+    if not (output_dir / ".git").exists():
+        subprocess.run(
+            ["git", "clone", CODSPEED_CPP_REPO, str(output_dir)],
+            check=True,
+        )
+    subprocess.run(
+        ["git", "-C", str(output_dir), "checkout", CODSPEED_CPP_SHA],
+        check=True,
+        capture_output=True,
+    )
+
+    benchmark_dir = output_dir / "google_benchmark"
+    core_dir = output_dir / "core"
+
+    # Create library.json combining google_benchmark + codspeed core
+    library_json = {
+        "name": "benchmark",
+        "version": "0.0.0",
+        "build": {
+            "flags": [
+                f"-I{core_dir / 'include'}",
+                f"-I{core_dir / 'instrument-hooks'}",
+                "-DHAVE_STD_REGEX",
+                "-DHAVE_STEADY_CLOCK",
+                "-DBENCHMARK_STATIC_DEFINE",
+            ],
+            "srcFilter": [
+                "+<src/*.cc>",
+                f"+<{core_dir / 'src' / '*.cpp'}>",
+            ],
+            "includeDir": "include",
+        },
+    }
+
+    (benchmark_dir / "library.json").write_text(
+        json.dumps(library_json, indent=2) + "\n"
+    )
+
+    return f"symlink://{benchmark_dir}"
+
+
+def main() -> None:
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument(
+        "--output-dir",
+        type=Path,
+        default=Path(DEFAULT_OUTPUT_DIR),
+        help=f"Directory to clone codspeed-cpp into (default: {DEFAULT_OUTPUT_DIR})",
+    )
+    args = parser.parse_args()
+
+    lib_path = setup_codspeed_lib(args.output_dir)
+    print(lib_path)
+
+
+if __name__ == "__main__":
+    main()