1) Deprecate CLASS_PATH_ENTRIES for removal, with javadoc explaining it will either be changed incompatibly or removed altogether in the next WF Core major.

This isn't used in full WF and I see no reason for extensions outside full WF to be using it. It's public because it's used in other server module packages. So this 'deprecate for removal' is really just following proper formalities.

2) Deprecate ADDITIONAL_ANNOTATION_INDEXES for removal, with javadoc explaining it will either be changed incompatibly or removed altogether in the next WF Core major.

This is actually used in full WF by the ee subsystem 'global module' feature, which is a quasi-kernel feature that got put in ee subsystem way back when before we knew better.

This 'deprecate for removal' gives any other uses in external extensions some notice that they will have to adapt. I don't see a reason other extensions would use this, so 'deprecate for removal' is really just following proper formalities.

3) Deprecate ADDITIONAL_ANNOTATION_INDEXES_BY_MODULE for removal, with javadoc explaining that new AttachmentKey ADDITIONAL_ANNOTATION_INDEXES_BY_MODULE_NAME should be used.

This key is used to pass data to the undertow subsystem. The kernel does not read the key ever. So create a new key and have the kernel attach that as well. When undertow switches to the new key we can remove the old one.

4) Deprecate MODULE_IDENTIFIER for removal, with javadoc explaining that new AttachmentKey MODULE_NAME should be used.

This is the most commonly used key. There's only one place that attaches the key (ModuleIdentifierProcessor) so it can attach the string form under new key MODULE_NAME as well.