Extract the shared flock/msvcrt boilerplate from _auth_store_lock and
_nous_shared_store_lock into a single _file_lock(lock_path, holder,
timeout, message) helper. Each caller keeps its own threading.local
holder so reentrancy state stays per-lock.
Also document the lock-ordering invariant on both wrappers:
_auth_store_lock is OUTER, _nous_shared_store_lock is INNER for all
runtime refresh paths. The one exception is _try_import_shared_nous_state,
which holds the shared lock alone across the full HTTP refresh+mint
cycle to prevent concurrent sibling imports from racing on the single-
use shared refresh token; that helper must not be called with the auth
lock already held.
429e78589b