Round-5 review nit on PR #920 (non-blocking): record_document_dead_lettered
increments alongside the fail-safe mark_dead_letter, so the counter measures the
dead-letter attempt and can sit marginally above the live marker count if a
Qdrant write fails. Note it in the docstring.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>