diff --git a/src/koru/init_host_environment.py b/src/koru/init_host_environment.py
index a0595c4d..23e30b04 100644
--- a/src/koru/init_host_environment.py
+++ b/src/koru/init_host_environment.py
@@ -6,7 +6,6 @@
 """
 
 
-import grp
 import json
 import os
 import shutil
@@ -16,6 +15,11 @@
 from pathlib import Path
 from typing import Any
 
+if sys.platform != "win32":
+    import grp as _grp
+else:
+    _grp = None  # type: ignore[assignment]
+
 from koru.ide_runtime import build_host_setup_report
 from koru.runtime import runtime_dir
 
@@ -69,7 +73,7 @@ def _uinput_snapshot() -> dict[str, Any]:
     except OSError as exc:
         return {"present": True, "stat_error": str(exc)}
     try:
-        group_name = grp.getgrgid(st.st_gid).gr_name
+        group_name = _grp.getgrgid(st.st_gid).gr_name if _grp is not None else str(st.st_gid)
     except (KeyError, OSError):
         group_name = str(st.st_gid)
     return {
diff --git a/tests/test_init.py b/tests/test_init.py
index 310c2d02..eef0dba0 100644
--- a/tests/test_init.py
+++ b/tests/test_init.py
@@ -26,7 +26,8 @@
     refresh_init_agent_lane,
     resolve_project_agent_lane,
 )
-from koru.init_host_environment import _parse_os_release_line
+import koru.init_host_environment as _ihe_mod
+from koru.init_host_environment import _parse_os_release_line, _uinput_snapshot
 from koru.policy import load_policy
 from koru.runtime import planfile_dir, runtime_dir
 
@@ -42,6 +43,23 @@ def test_parse_os_release_line(self) -> None:
         self.assertIsNone(_parse_os_release_line("MALFORMED"))
         self.assertIsNone(_parse_os_release_line("=missing-key"))
 
+    def test_grp_sentinel_matches_platform(self) -> None:
+        """_grp must be None on Windows and the real grp module elsewhere."""
+        import sys
+
+        if sys.platform == "win32":
+            self.assertIsNone(_ihe_mod._grp)
+        else:
+            import grp
+
+            self.assertIs(_ihe_mod._grp, grp)
+
+    def test_uinput_snapshot_absent_device(self) -> None:
+        """_uinput_snapshot returns present=False when /dev/uinput does not exist."""
+        result = _uinput_snapshot()
+        # On CI / Windows / macOS /dev/uinput is absent; the function must not raise.
+        self.assertIn("present", result)
+
 
 def _detach_ci_env() -> dict[str, str]:
     """Remove CI markers so IDE folder detection is deterministic in tests."""