The worker loaded the tenant extension for the poller (schema discovery)
but did not pass it to MemoryEngine. When execute_task set _current_schema
via the _schema field, _authenticate_tenant would immediately reset it to
"public" because self._tenant_extension was None, causing all worker writes
to land in the public schema instead of the tenant schema.
Move load_extension() before MemoryEngine creation and pass
tenant_extension to the constructor.
