"AutoloadNamespaces": { "EchoOOUI\\": "includes/ooui/", "EchoPush\\": "includes/Push/", "EchoPush\\Api\\": "includes/api/Push/" },
As per https://www.mediawiki.org/wiki/Best_practices_for_extensions
SHOULD: Classes in MediaWiki\Extension\<ExtensionName> namespace. MediaWiki\<ExtensionName> is permissible if the extension name is a sufficiently unique word and not something generic (e.g. not a verb or noun).
I don't think Echo is necessarily something sufficiently unique... But having EchoOOUI and EchoPush doesn't seem right.