fix: eliminate -B double-dispatch through mock system

lib/Overload/FileCheck.pm

@@ -288,7 +288,7 @@ sub _check_from_stat {
     # 2/ doing a second stat call in order to cache _
 
     my $can_use_stat;
-    $can_use_stat = 1 if $check =~ qr{^[sfdMXxzACORWeorwugk]$};
+    $can_use_stat = 1 if $check =~ qr{^[sfdMXxzACORWeorwugkBT]$};
 
     my $stat_or_lstat = $can_use_stat ? 'stat' : 'lstat';
 
@@ -342,7 +342,7 @@ sub _check_from_stat {
         # Heuristic text/binary checks (use glob _ to pass the cached stat)
         T => sub { _xs_unmock_op($optype); _to_bool( scalar -T *_ ) },   # ASCII or UTF-8 text (heuristic)
         B => sub {                                                         # binary file (opposite of -T)
-            return CHECK_IS_TRUE if -d $f_or_fh;
+            return CHECK_IS_TRUE if @stat && ( $stat[ST_MODE] & _S_IFMT ) == S_IFDIR;
             _xs_unmock_op($optype);
             return _to_bool( scalar -B *_ );
         },

t/B-no-double-dispatch.t

@@ -0,0 +1,61 @@
+#!/usr/bin/perl -w
+
+# Verify that the -B handler in _check_from_stat does not re-enter the
+# mock system by calling "-d $f_or_fh".  Before the fix, the -B handler
+# triggered a second stat callback through the mocked -d operator,
+# wasting a round-trip and risking side-effect divergence.
+
+use strict;
+use warnings;
+
+use Test2::Bundle::Extended;
+use Test2::Tools::Explain;
+use Test2::Plugin::NoWarnings;
+
+use Overload::FileCheck q(:all);
+
+my $stat_call_count = 0;
+
+# Track how many times the stat callback is invoked per -B check.
+mock_all_from_stat(
+    sub {
+        my ( $op, $file ) = @_;
+
+        return FALLBACK_TO_REAL_OP unless defined $file;
+        return FALLBACK_TO_REAL_OP unless $file =~ m{^MOCK/};
+
+        $stat_call_count++;
+
+        if ( $file eq 'MOCK/regular-file' ) {
+            return stat_as_file( size => 100 );
+        }
+
+        if ( $file eq 'MOCK/a-directory' ) {
+            return stat_as_directory();
+        }
+
+        return [];    # file not found
+    }
+);
+
+# -B on a mocked regular file: stat callback should be called exactly once
+$stat_call_count = 0;
+my $result = -B 'MOCK/regular-file';
+is $stat_call_count, 1, '-B on regular file triggers stat callback exactly once (no double-dispatch)';
+
+# -B on a mocked directory: stat callback should be called exactly once
+# and -B should return true (directories are "binary" in Perl)
+$stat_call_count = 0;
+$result = -B 'MOCK/a-directory';
+is $stat_call_count, 1, '-B on directory triggers stat callback exactly once (no double-dispatch)';
+ok $result, '-B on directory returns true';
+
+# -B on a non-existent mocked file: stat callback should be called exactly once
+$stat_call_count = 0;
+$result = -B 'MOCK/no-such-file';
+is $stat_call_count, 1, '-B on non-existent file triggers stat callback exactly once';
+
+unmock_all_file_checks();
+unmock_stat();
+
+done_testing;