A plugin's register() runs on a plugin-load deadline worker. When it re-walks
the platform registry (i18n/YAML layering -> plugin_entries()), _resolve sees
its own parent's in-flight loader, but ownership was keyed on
threading.get_ident() -- the parent's thread, not the worker -- so the nested
walk event.wait()ed on itself until the deadline abandoned the load (#130575).
Record in-flight load keys in a per-registry ContextVar instead. Deadline
workers start from copy_context(), so a nested walk on the parent's worker
takes the existing "recursively requested while loading" return, while
unrelated concurrent loaders (fresh contexts) still wait on the event.
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