Remove error_notifier from public API

[bolshakov]

The error_notifier option has never been documented in the README and may cause confusion for users.

In the Stoplight function documentation, it’s currently described as:

# @option settings [Proc] :error_notifier A proc to handle error notifications.

This phrasing could misleadingly suggest that the proc reports any errors occurring during the execution of user code. However, this is not the case. The error_notifier is used internally by Stoplight to report internal failures - for example, when the Redis data store fails. In such cases, Stoplight falls back to the in-memory data store while using this notifier to log or report the internal error.

To make its purpose clearer and prevent misuse, I propose moving this configuration option to the global configuration only, disallowing per-light configuration.

Stoplight.configure do |config|
  config.error_notifier = ->(error) { warn error }
end

This makes it explicit that the error_notifier applies globally and is intended solely for internal error reporting.

[chaadow]

Hi, I don't understand this part:

The error_notifier option has never been documented in the README.

It is documented here: https://github.com/bolshakov/stoplight?tab=readme-ov-file#error-notifiers

[bolshakov]

@chaadow you're right, it's documented as part of the configuration API. However, not documented as part of the Stoplight creation API:

Stoplight(name, error_notifier:)

My idea is to disallow uses like above. My concern is that this option could be a bit confusing - I saw examples when people pass error_notifier and expect it to send them exceptions from the protected code in scenarios like this:

Stoplight(name, error_notifier:).run(->(e) { follback_behaviour } do 
   # ... code that raises an exception 
end

In this example, the error is swallowed because of the fallback behaviour, and sometimes users expect the error notifier to report them too.

[bolshakov]

@chaadow I explained my thinking here #533