I haven't tested this but believe it is cleaner to write as

sub commit () {
    ($T || ${ caller() . '::T' })->commit;
    goto END_XACTION;
}

sub rollback () {
    ($T || ${ caller() . '::T' })->rollback;
    goto END_XACTION;
}

sub transaction (&) {
    my ($block) = @_;
    local $T = ${ caller() . '::T' } or croak "\$T not set";

    local $@;
    eval {
        $T->begin_work;
        $block->();
    };
    $@ ? rollback : commit;

    END_XACTION: die $@ . "commit not safe after errors, transaction r
+olled back"
        if $@;
}
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I would suggest you work with die instead though - that will work with nested transactions and require fewer hoop jumps. You can then also easily add some more error checking:

sub commit {
    require Carp;
    Carp::croak("Can't commit outside a transaction");
}

sub rollback {
    require Carp;
    Carp::croak("Can't rollback outside a transaction");
}


sub transaction (&) {
    my ($block) = @_;

    my $caller = caller();

    local *{"${caller}::commit"} = sub { die "!COMMIT\n" };
    local *{"${caller}::rollback"} = sub { die "!ROLLBACK\n" };

    local $@;
    eval {
        $T->begin_work;
        $block->();
    };

    if(!$@ or $@ eq "!COMMIT\n") {
        ${"${caller}::T"}->commit;
    }
    elsif($@ eq "!ROLLBACK\n") {
        ${"${caller}::T"}->rollback;
    }
    else {
        ${"${caller}::T"}->rollback;

        require Carp;
        Carp::croak($@ . "commit not safe after errors, transaction ro
+lled back");
    }
}
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Makeshifts last the longest.