Site Editor should display a 404 message when you navigate to a non-existing path

[carolinan]

Description

With a block theme and Gutenberg trunk active, if you open the Site Editor but miss-type the link, the Site Editor is now a black page with no message or content showing.

Without Gutenberg active, you are presented with the index template (Or home blog or front page, if the theme uses that)

Step-by-step reproduction instructions

Try navigating to wp-admin/site-editor.php?p=%2Ftemplate-fdgfdgdfg.

Screenshots, screen recording, code snippet

No response

Environment info

No response

Please confirm that you have searched existing issues in the repo.

• Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

• Yes

Please confirm which theme type you used for testing.

• Block
• Classic
• Hybrid (e.g. classic with theme.json)
• Not sure

[carolinan]

@youknowriad I believe this is related to #67199.

[youknowriad]

Yes, we discussed this in the PR. We should define a real 404 page instead of showing the home page like before.