Trying to figure out why timeout errors cause commits

timeout_test.rb

require 'timeout'

# loosely based on https://github.com/rails/rails/blob/v4.2.7.1/activerecord/lib/active_record/connection_adapters/abstract/transaction.rb#L182-L201
def transaction
  yield

rescue Exception => error
  STDERR.puts "Rescued exception: #{error.to_s}"
  raise

ensure
  STDERR.puts "Ensuring..."
  unless error
    status = Thread.current.status
    STDERR.puts "Error was falsey, trying to commit transaction! (current thread status #{status.inspect})"
  end
end

class CustomTimeoutError < RuntimeError
  def to_s
    "Custom Timeout Error"
  end
end

# loosely based on openstreetmap-website/app/controller/application_controller.rb:345
def api_call_timeout(custom_error = nil)
  Timeout.timeout(1, custom_error) do
    yield
  end
rescue Timeout::Error
  STDERR.puts "Rescued API call timeout."
  raise CustomTimeoutError
end

# when transaction wraps timeout, all is okay:
STDERR.puts "transaction { api_call_timeout { ... } }"
begin
  transaction { api_call_timeout { sleep 2 } }
rescue Exception => e
  STDERR.puts "Top level rescue: #{e.to_s}"
end
STDERR.puts

# when timeout wraps transaction, it attempts to commit the transaction
STDERR.puts "api_call_timeout { transaction { ... } }"
begin
  api_call_timeout { transaction { sleep 2 } }
rescue Exception => e
  STDERR.puts "Top level rescue: #{e.to_s}"
end
STDERR.puts

# Fix is to use Timeout.timeout to inject a custom exception?
STDERR.puts "api_call_timeout(CustomTimeoutError) { transaction { ... } }"
begin
  api_call_timeout(CustomTimeoutError) { transaction { sleep 2 } }
rescue Exception => e
  STDERR.puts "Top level rescue: #{e.to_s}"
end
STDERR.puts