The comment said the lock is an RLock because save_config internally
calls read_raw_config. After the previous fix that is no longer true:
save_config takes its raw mapping from require_readable_config_before_write
and never re-enters the lock through read_raw_config.
The reentrancy that still exists is external: hermes_cli/plugins.py holds
_CONFIG_LOCK across its read-modify-write and then calls save_config(),
which acquires the lock again. Name that, and leave the RLock as is.
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