Subscribe to `Rails.error` automatically again?

@solnic đang làm issue này rồi.

Từ ngày 14/1/2026.

### Problem Statement

In order to subscribe to Error Reporter aka `Rails.error` (https://api.rubyonrails.org/classes/ActiveSupport/ErrorReporter.html) we need to set `config.rails.register_error_subscriber = true` since 5.3.0 (cf. #1771).

This is possibly confusing, when [Error Reporting in Rails Applications](https://guides.rubyonrails.org/error_reporting.html#subscribing-to-the-reporter) is eager to assume the integration takes place just automatically, as it says;

> Some error-reporting libraries, such as Sentry's and Honeybadger's, automatically register a subscriber for you.

It would be great if the subscription happens automatically just like the guide emphasizes. If it's still up to users to opt in to the feature, it could be the guide misinforming. In any case I think there is a chance for improvement.

### Solution Brainstorm

According to #1771, the decision to disable the integration by default looks like a compromise given that Rails 7.0's error reporter had an issue. Reading further the feedback thread at https://github.com/rails/rails/pull/43625#issuecomment-1072514175 and following https://github.com/rails/rails/pull/44998 then #1834, is it possible to assume the issue has been resolved and it is ready to make the subscriber registered automatically for applications whose Rails version is 7.1 or higher?