Kotlin backwards compatibility for annotated Java libraries

I noticed this interesting compilation error on a kotlin wrapper for Caffeine when it attempted to upgrade the dependency to the JSpecify annotated version. Here's a cleaned up error message for their CoroutineAsyncCacheLoader.

CoroutineAsyncCacheLoaders.kt:26:8 
    Return type of 'asyncLoad' is not a subtype of the return type of the overridden member
    'fun asyncLoad(key: K, executor: Executor): CompletableFuture<out V>' defined in 'CoroutineAsyncCacheLoader'.
CoroutineAsyncCacheLoaders.kt:32:8 
    Return type of 'asyncReload' is not a subtype of the return type of the overridden member 
    'fun asyncReload(key: K, oldValue: @NonNull() V & Any, executor: Executor): CompletableFuture<out V>' defined in 'CoroutineAsyncCacheLoader'.
CoroutineCacheImpl.kt:18:43 
    Argument type mismatch: actual type is 'V?', but 'V' was expected.
> Task :caffeine-coroutines:compileKotlin FAILED

Is it expected that when Java libraries adopt nullability annotations, downstream Kotlin users should expect these types of compilation failures? Is this strictly a source incompatible change or are there binary compatibility aspects that Kotlin imposes on their call sites to be aware of?

Start with the linked caffeine-coroutines pull request and the referenced CoroutineAsyncCacheLoaders.kt and CoroutineCacheImpl.kt files, then compare the Kotlin compiler errors with the Java API's nullability annotations. Determine whether adopting annotations creates source or binary compatibility changes for Kotlin callers, and record the compatibility guidance or required follow-up.