The network-error reconnect ladder (#55992) captured a stable self._app
local across its awaits and failed fast when the adapter was torn down
mid-sleep. The 409-conflict retry path had the identical unguarded
self._app.updater.start_polling() deref — a concurrent disconnect()
during its RETRY_DELAY sleep would raise the same 'NoneType' object has
no attribute 'updater' and, on a non-final retry, land in limbo. Apply
the same stable-local + fail-fast pattern so the existing except block
reschedules or escalates to fatal.
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