Great breakdown – this reminds me of a pattern I’ve been building recently in .NET called StackWeaver.
It's a service metadata registry that tracks layers, dependencies, and fallback capabilities across large-scale systems.
It’s not low-level like AQS, but it models fallback paths, callbacks and failure detection at the application architecture level.

Your analysis of tail == null and relaxed writes made me wonder if the same state-tracking principles could be represented or orchestrated in a metadata-driven way.

If you're curious, I'd love to hear what you think:
→ Modular .NET service registry with metadata, tagging and .bat execution (StackWeaver project)
(also on GitHub soon)

Thanks again for the deep dive – this was fun to read!

First try here :)