+1 for additive. I like the clean approach to declare your dependencies explicitly.

but disable the whole dirty-checking optimisation by default on each entity

You mean having the ability to do so with enableDirtyCheckingOptimisations=true or change the default entirely?

+1 to add the ability to disable the optimizations: we used to add an empty ClassBridge to do so but it's better if the semantic is clear and we have a clean way to do it.

-1 to change the default

+1 to add a section in the documentation talking about these issues.

And maybe an entity having @Transient properties which affect input of any index field (be it via @Field of custom bridges) should always be considered dirty, at least by default?

AFAIK, it's already the case.

I'm wondering if, instead of creating a new annotation, we could include it in the @Field annotation. Something like a dependsOn attribute taking a list of properties? If not empty, it would disable the automatic shutting down of the optimizations on @Transient fields and consider these properties.