This is one of the VisualEditor 404 errors that affects developers using the master branch (1.36-alpha).
Parsoid auto configuration that was introduced in 1.35 was a temporary solution for the LTS. Pending a final solution this was removed in patch 622187.
Workaround for the time being:
add to LocalSettings.php
// For 1.36-alpha only wfLoadExtension( 'Parsoid', 'vendor/wikimedia/parsoid/extension.json' );
See also:
- https://www.mediawiki.org/wiki/Extension:VisualEditor#Linking_with_Parsoid
- https://www.mediawiki.org/wiki/Parsoid#Linking_a_developer_checkout_of_Parsoid
Split from T263928#6593539