Scope open-registration and rename/remove ordering to overlapping paths;
let descriptor mutations and directory creation proceed without that lock.
Prove blocked opens/writes cannot stall unrelated namespaces, including a
queued rename, and retain post-rename descriptor notifications. Document
handler-owned watch lifetimes and narrow paths; test natural idle exit.
Card: SAU-359
Register core.watch before its armed notification, coalesce later changes
without losing post-notification writes, and clean up on caller death.
Observe mounted layers and open file handles, including descriptor/stream
writes, truncation, both rename paths and deletion. Track cancelled
mutations through process idle and retain visible paths across renames.
Document the protocol, expose native core discovery, and exercise watches
through SDK callbacks and raw WASI filesystem operations.
Card: SAU-359