The SDK drives a refresh as a generator (request yielded from
_refresh_token, response consumed in _handle_refresh_response), so the
fence was a hand-driven @asynccontextmanager: __aenter__ in one method,
__aexit__ in another, generator object stashed on the provider. A plain
`acquire_refresh_fence(path, timeout) -> fd` / `release_refresh_fence(fd)`
pair says what actually happens and leaves nothing half-entered to leak.
The descriptor is opened with os.open at 0600 and closed on every
acquisition failure.
The `_refresh_token` release-on-exception stays: `_refresh_token` is also
reachable outside `async_auth_flow` (tests call it directly), and the
wrapper's finally only covers the generator-driven path.
HermesTokenStorage.remove() now unlinks the `.refresh.lock` sibling so
logout leaves no stray file. It is deliberately NOT added to
_state_paths(): snapshot()/restore(only_if_absent=True) treat any
existing state path as "newer state exists", and a lingering lock file
would silently veto a rollback.
tests/tools/test_mcp_oauth.py: drop the unused `Path` import (`time` is
still used by the socket poll helper).
60262f71bd