The final observation relation has exactly these required semantic fields:
document_id, hpo_id, start_offset, end_offset, source_text,
context_status, method, provider_id, provider_version,
confidence, and status. Offsets are zero-based, half-open R character
offsets. Lexical candidates returned by ducksemantics_annotate() are not
observations and cannot be substituted for this relation.