fix: prevent filehandle reference leak in stat override

lib/Overload/FileCheck.pm

@@ -584,7 +584,10 @@ sub _check {
 
     $file = $_last_call_for if !defined $file && defined $_last_call_for && !defined $_current_mocks->{ $MAP_FC_OP{'stat'} };
     my ( $out, @extra ) = $_current_mocks->{$optype}->($file);
-    $_last_call_for = $file;
+    # Only cache string filenames, not filehandle references.
+    # Storing a ref here prevents the filehandle from being garbage collected,
+    # causing resource leaks (e.g. sockets staying open). See GH #179.
+    $_last_call_for = ref($file) ? undef : $file;
 
     # FIXME return undef when not defined out
 

t/fh-ref-leak.t

@@ -0,0 +1,66 @@
+#!/usr/bin/perl
+
+# Test that file check operators do not retain references to filehandles
+# passed as arguments. This prevents garbage collection of the filehandle,
+# which can cause resource leaks (e.g. sockets staying open).
+#
+# See: https://github.com/cpanel/Test-MockFile/issues/179
+
+use strict;
+use warnings;
+
+use Test2::Bundle::Extended;
+use Test2::Tools::Explain;
+
+use Scalar::Util qw(weaken);
+use Overload::FileCheck -from_stat => \&my_stat, qw{:check};
+
+sub my_stat {
+    my ( $stat_or_lstat, $f ) = @_;
+    return FALLBACK_TO_REAL_OP();
+}
+
+# Test that filehandle references are not retained by $_last_call_for
+{
+    my $weak_ref;
+
+    {
+        open my $fh, '<', '/dev/null' or die "Cannot open /dev/null: $!";
+        $weak_ref = $fh;
+        weaken($weak_ref);
+
+        ok( defined $weak_ref, "weak ref is defined before scope exit" );
+
+        # Trigger a file check on the filehandle — this used to store $fh
+        # in $_last_call_for, preventing garbage collection.
+        no warnings;
+        -f $fh;
+    }
+
+    ok( !defined $weak_ref, "filehandle is garbage collected after -f check (no ref leak)" );
+}
+
+# Test with -S (the operator from the original bug report)
+{
+    my $weak_ref;
+
+    {
+        open my $fh, '<', '/dev/null' or die "Cannot open /dev/null: $!";
+        $weak_ref = $fh;
+        weaken($weak_ref);
+
+        no warnings;
+        -S $fh;
+    }
+
+    ok( !defined $weak_ref, "filehandle is garbage collected after -S check (no ref leak)" );
+}
+
+# Test that string filenames still work for _ caching (no regression)
+{
+    no warnings;
+    ok( -f $0,  "-f \$0 works" );
+    ok( -e _,   "-e _ works after -f on string filename" );
+}
+
+done_testing;