The commit that added
lock_thread (f638085) notes that
> Transaction management is largely ripped straight out of
> test_fixtures.rb in Rails

The commit that adds lock_thread in Rails --
rails/rails@d6466be
-- has some helpful context:
> When a system test starts Puma spins up one thread and Capybara spins
> up another thread. Because of this when tests are run the database
> cannot see what was inserted into the database on teardown. This is
> because there are two threads using two different connections.

> This change uses the statement cache to lock the threads to using a
> single connection ID instead of each not being able to see each other.

So lock_thread exists because there are two different threads -- Puma
and Capybara -- trying to access the same database but not necessarily
seeing the same thing. But! cypress-rails doesn't use Capybara, and more
importantly, it doesn't use tests or a test runner written in Ruby at
all, so there's only _one_ thread trying to use the database. So we
don't need all this thread locking stuff. So let's remove it to make
things more compatible with Rails 7.2.