Actually, I'm surprised that it works at all.
META-INF/services is poor man's service registry that only works well in a Java SE classpath and is notoriously hard to use in multi-classloader environments like OSGi or Java EE.
Given that CDI is implemented as an OSGi bundle within the container and your extension lives in your web app, I wouldn't expect the Weld class loader to be able to see the META-INF/services resources from the web app class loader handling your extension jar.
Magic indeed...
Best regards,
Harald
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