_read_events() returned normally when self._ws was closed-but-non-None
(the while-condition is false on entry). _listen_loop treats a normal
return as a clean read, resets backoff to 0, and immediately retries —
a tight busy-loop pinning CPU. Raising on entry routes it through the
reconnect/backoff path instead.
Co-authored-by: xushibo <xushibo@users.noreply.github.com>
Co-authored-by: cnfi <cnfi@users.noreply.github.com>
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