Recovery mode page references checking your site admin email, even in Multisite

[rkaiser0324]

In display_default_error_template() the message references checking your email if the endpoint is protected. However, in WP_Fatal_Error_Handler::handle() it will never call handle_error() if is_multisite() is true.

So the error message is misleading in that case, so no email was actually sent.

The error message shouldn't reference checking your email if no email sending was attempted.

[Clorith]

Thank you very much for your report of this @rkaiser0324, you are quite right that this is text was misleading.

48929.patch​ is a suggested resolution, where the text is more aware of the current site setup, providing different texts if it is a protected endpoint, but you are, or are not, on a multisite install.

Standalone site:

There has been a critical error on this website. Please check your site admin email inbox for instructions.

Multisite:

There has been a critical error on this website. Please reach out to your site administrator, and inform them of this error for further assistance.

I opted for the term site administrator over network administrator, as the last one also has meanings for businesses where this is also used as the term for whomever handles networking issues in the office or similar.

[Clorith]

In 53951:

Site Health: Improve the fatal error handling text in multisite scenarios.

The fatal error handler is responsible for providing a more user-friendly page to visitors if a site would normally encounter a fatal error, informing them of the next steps to access recovery mode (where applicable).

Those next steps would be to check the email address for the site administrator, but this was only the case for single site installs; In a multisite scenario, no email is sent.

This changes the text to account for that, still informing site administrators to check their email if it is a single site, but for multisite directing users to reach out to their site administrator for further assistance, so that they may take appropriate action.

Props rkaiser0324, Clorith.
Fixes #48929.