[None][fix] Install with the venv interpreter, not sys.executable

scripts/build_wheel.py

@@ -768,6 +768,17 @@ def stage_python_package(project_dir: Path, staging_dir: Path) -> None:
             copy(src, staging_dir / name)
 
 
+def install_editable_package(venv_python: Path) -> None:
+    """Editable-install the built package into the venv `setup_venv` created.
+
+    Not `sys.executable`: a fresh checkout has to start this script with the
+    system interpreter, so installing with it puts the package in the system
+    site-packages and leaves the new venv without it. The wheel build above
+    already uses `venv_python` for the same reason.
+    """
+    build_run(f"\"{venv_python}\" -m pip install -e .[devel]")
+
+
 def main(*,
          build_type: str = "Release",
          generator: str = "",
@@ -1523,7 +1534,7 @@ def get_binding_lib(subdirectory, name):
             env=env)
 
     if install:
-        build_run(f"\"{sys.executable}\" -m pip install -e .[devel]")
+        install_editable_package(venv_python)
 
 
 def add_arguments(parser: ArgumentParser):

tests/unittest/others/test_build_wheel_install_interpreter.py

@@ -0,0 +1,47 @@
+# SPDX-FileCopyrightText: Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+# SPDX-License-Identifier: Apache-2.0
+"""``build_wheel.py --install`` must use the venv interpreter.
+
+A fresh checkout has to start ``build_wheel.py`` with the system interpreter,
+so installing with ``sys.executable`` puts the package into the system
+site-packages and leaves the venv that ``setup_venv()`` just created without
+it. The install has to run with ``venv_python``.
+"""
+
+import importlib.util
+import sys
+from pathlib import Path
+
+import pytest
+
+_BUILD_WHEEL = Path(__file__).resolve().parents[3] / "scripts" / "build_wheel.py"
+
+
+@pytest.fixture(scope="module")
+def build_wheel():
+    """``scripts/build_wheel.py`` loaded by path.
+
+    It is a script rather than a package member. Importing it runs only its
+    imports and constants; ``main()`` is behind the usual ``__main__`` guard.
+    """
+    assert _BUILD_WHEEL.is_file(), _BUILD_WHEEL
+    spec = importlib.util.spec_from_file_location("_build_wheel_under_test", _BUILD_WHEEL)
+    module = importlib.util.module_from_spec(spec)
+    sys.modules[spec.name] = module
+    spec.loader.exec_module(module)
+    yield module
+    sys.modules.pop(spec.name, None)
+
+
+def test_install_runs_with_the_venv_interpreter(build_wheel, monkeypatch, tmp_path):
+    commands = []
+    monkeypatch.setattr(build_wheel, "build_run", lambda cmd, **kwargs: commands.append(cmd))
+
+    venv_python = tmp_path / "venv" / "bin" / "python"
+    build_wheel.install_editable_package(venv_python)
+
+    assert len(commands) == 1
+    command = commands[0]
+    assert command.startswith(f'"{venv_python}" -m pip install -e ')
+    assert str(venv_python) in command
+    assert sys.executable not in command