diff --git a/internal/sandbox/manager_test.go b/internal/sandbox/manager_test.go
index ee93d11e2..5dc754acf 100644
--- a/internal/sandbox/manager_test.go
+++ b/internal/sandbox/manager_test.go
@@ -72,6 +72,9 @@ func TestPermissionProfileFromPolicyIncludesDefaultTempWriteRoots(t *testing.T)
 	if !writeRootsContain(profile.FileSystem.WriteRoots, tmpdir) {
 		t.Fatalf("write roots = %#v, want temp root %q", profile.FileSystem.WriteRoots, tmpdir)
 	}
+	// /tmp is a default temp write root on POSIX only (see
+	// defaultTempWriteRootCandidatesForGOOS); on Windows the bare path resolves
+	// against the current drive, so a stray C:\tmp must not turn this on.
 	if runtime.GOOS != "windows" && pathExists("/tmp") && !writeRootsContain(profile.FileSystem.WriteRoots, "/tmp") {
 		t.Fatalf("write roots = %#v, want /tmp", profile.FileSystem.WriteRoots)
 	}
diff --git a/internal/sandbox/scope_test.go b/internal/sandbox/scope_test.go
index 6dc7a146b..3714c75f2 100644
--- a/internal/sandbox/scope_test.go
+++ b/internal/sandbox/scope_test.go
@@ -129,6 +129,9 @@ func TestNewScopeNormalizesAndValidatesExtraRoots(t *testing.T) {
 	if !stringSliceContains(roots, normalizeWorkspaceRootBestEffort(extra)) {
 		t.Fatalf("Roots()=%v want extra root %q", roots, normalizeWorkspaceRootBestEffort(extra))
 	}
+	// /tmp is a default temp write root on POSIX only (see
+	// defaultTempWriteRootCandidatesForGOOS); on Windows the bare path resolves
+	// against the current drive, so a stray C:\tmp must not turn this on.
 	if runtime.GOOS != "windows" && pathExists("/tmp") && !stringSliceContains(roots, normalizeWorkspaceRootBestEffort("/tmp")) {
 		t.Fatalf("Roots()=%v want default /tmp write root", roots)
 	}