When create_letzshop_order raises an exception (e.g., product not found by GTIN)
after flushing the order to the database, the session is left in an inconsistent
state. Without rollback, subsequent database operations fail or hang, causing
the import to get stuck at "0 processed...".
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>