fix: migrate open file handles to new mock on rename

lib/Test/MockFile.pm

@@ -4125,6 +4125,24 @@ sub __rename ($$) {
     $mock_new->{'mtime'} = $mock_old->{'mtime'};
     $mock_new->{'atime'} = $mock_old->{'atime'};
 
+    # Migrate open file handles from old mock to new mock.
+    # Unix semantics: open fds follow the inode, not the directory entry.
+    # Each tied FileHandle has a weak 'data' ref that must be re-pointed.
+    if ( $mock_old->{'fhs'} && @{ $mock_old->{'fhs'} } ) {
+        $mock_new->{'fhs'} //= [];
+        for my $fh_ref ( @{ $mock_old->{'fhs'} } ) {
+            next unless defined $fh_ref;
+            my $tied = ref $fh_ref ? tied( *{$fh_ref} ) : undef;
+            if ($tied) {
+                $tied->{'data'} = $mock_new;
+                Scalar::Util::weaken( $tied->{'data'} );
+                $tied->{'file'} = $mock_new->{'path'};
+            }
+            push @{ $mock_new->{'fhs'} }, $fh_ref;
+        }
+        $mock_old->{'fhs'} = [];
+    }
+
     # rename updates ctime on both source and destination
     my $now = time;
     $mock_new->{'ctime'} = $now;

t/rename_open_handle.t

@@ -0,0 +1,99 @@
+use strict;
+use warnings;
+
+use Test2::Bundle::Extended;
+use Test2::Tools::Explain;
+use Test2::Plugin::NoWarnings;
+
+use Test::MockFile qw< nostrict >;
+
+subtest 'read continues after rename' => sub {
+    my $old = Test::MockFile->file( '/fake/old.txt', 'Hello World' );
+    my $new = Test::MockFile->file( '/fake/new.txt', '' );
+
+    open( my $fh, '<', '/fake/old.txt' ) or die "open: $!";
+    my $buf;
+    read( $fh, $buf, 5 );
+    is( $buf, 'Hello', 'read before rename' );
+
+    rename( '/fake/old.txt', '/fake/new.txt' ) or die "rename: $!";
+
+    # Unix semantics: open fd survives rename — data follows the inode.
+    read( $fh, $buf, 6 );
+    is( $buf, ' World', 'read after rename sees remaining data' );
+
+    close $fh;
+};
+
+subtest 'write continues after rename' => sub {
+    my $old = Test::MockFile->file( '/fake/w_old.txt', 'AB' );
+    my $new = Test::MockFile->file( '/fake/w_new.txt', '' );
+
+    open( my $fh, '+<', '/fake/w_old.txt' ) or die "open: $!";
+
+    rename( '/fake/w_old.txt', '/fake/w_new.txt' ) or die "rename: $!";
+
+    # Write should go to the new location's data.
+    print $fh 'XY';
+    close $fh;
+
+    is( $new->contents, 'XY', 'write after rename lands in new mock' );
+};
+
+subtest 'tell preserved after rename' => sub {
+    my $old = Test::MockFile->file( '/fake/t_old.txt', 'ABCDEF' );
+    my $new = Test::MockFile->file( '/fake/t_new.txt', '' );
+
+    open( my $fh, '<', '/fake/t_old.txt' ) or die "open: $!";
+    my $buf;
+    read( $fh, $buf, 3 );
+    is( tell($fh), 3, 'tell before rename' );
+
+    rename( '/fake/t_old.txt', '/fake/t_new.txt' ) or die "rename: $!";
+
+    is( tell($fh), 3, 'tell unchanged after rename' );
+    read( $fh, $buf, 3 );
+    is( $buf, 'DEF', 'continue reading from correct position' );
+
+    close $fh;
+};
+
+subtest 'multiple handles survive rename' => sub {
+    my $old = Test::MockFile->file( '/fake/m_old.txt', 'DATA' );
+    my $new = Test::MockFile->file( '/fake/m_new.txt', '' );
+
+    open( my $fh1, '<', '/fake/m_old.txt' ) or die "open1: $!";
+    open( my $fh2, '<', '/fake/m_old.txt' ) or die "open2: $!";
+
+    # Advance fh1 but not fh2
+    my $buf;
+    read( $fh1, $buf, 2 );
+
+    rename( '/fake/m_old.txt', '/fake/m_new.txt' ) or die "rename: $!";
+
+    read( $fh1, $buf, 2 );
+    is( $buf, 'TA', 'handle 1 continues from tell=2' );
+
+    read( $fh2, $buf, 4 );
+    is( $buf, 'DATA', 'handle 2 reads full contents from tell=0' );
+
+    close $fh1;
+    close $fh2;
+};
+
+subtest 'eof works after rename' => sub {
+    my $old = Test::MockFile->file( '/fake/e_old.txt', 'AB' );
+    my $new = Test::MockFile->file( '/fake/e_new.txt', '' );
+
+    open( my $fh, '<', '/fake/e_old.txt' ) or die "open: $!";
+    my $buf;
+    read( $fh, $buf, 2 );
+
+    rename( '/fake/e_old.txt', '/fake/e_new.txt' ) or die "rename: $!";
+
+    ok( eof($fh), 'eof returns true after rename when at end' );
+
+    close $fh;
+};
+
+done_testing();