Exception message is missing with Capybara.raise_server_errors == true

[Jason Barnabe]

Meta

Capybara Version: 3.39.2
Driver Information (and browser if relevant): selenium-driver 4.12.0, Chrome

Expected Behavior

With Capybara.raise_server_errors = true, I expect the output of my tests to include full information on any server exceptions.

Actual Behavior

Output includes exception class, stack trace, but is missing exception message. For example, if in my Rails controller I put raise 'My exception details', I get:

Error:
MySystemTest#test_error:
RuntimeError: {:cause=>#<Capybara::CapybaraError: Your application server raised an error - It has been raised in your test code because Capybara.raise_server_errors == true>}
    app/controllers/my_controller.rb:12:in `show'

No My exception details anywhere.

I believe this is a regression from fa978af. If I revert that, then I get the message.

Error:
MySystemTest#test_error:
RuntimeError: My exception details
    app/controllers/my_controller.rb:12:in `show'

[Thomas Walpole]

What version of ruby, and what output formatter are you using because doing the same in the Capybara test suite outputs ```
Failure/Error: raise 'My exception details'

 RuntimeError:
   My exception details
 # ./lib/capybara/spec/test_app.rb:161:in `block in <class:TestApp>'
 # ./lib/capybara/server/middleware.rb:60:in `call'
 # ------------------
 # --- Caused by: ---
 # Capybara::CapybaraError:
 #   Your application server raised an error - It has been raised in your test code because Capybara.raise_server_errors == true
 #   ./lib/capybara/session.rb:164:in `raise_server_error!'

[Jason Barnabe]

I'm using Ruby 3.2.2. Not sure what output formatter I'm using or how to figure it out, but I'm using minitest.

[Thomas Walpole]

Can you produce a small self-contained example to reproduce this?