_send_file hit the identical stale -2 after its own tokenless re-send and still
raised the generic "sendmessage error"; it now raises the shared
_session_not_ready_error. The genuine rate-limit cooldown message carries
ret/errcode/errmsg so operators can tell a real -2 frequency limit from the
session case. One parametrised test (stored token / no token) asserts the send
fails once, classify_send_error does not call it rate_limited, and the breaker
stays closed; troubleshooting row in the Weixin docs.
5db9f02372