zmDbDo suppresses its Error log on 1213 inside a caller-managed TX (the
caller owns the retry), and the previous fallthrough at the end of the
retry loop just `return`ed silently. After 5 failed attempts on persistent
contention the event was effectively un-deleted with no record of the
failure. Capture errstr before rollback (some drivers clear it) and emit
an Error on the bail path.
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