Fields from the meta/sample sources need edit_post_meta (update, checked in PostWriter::prepare) or add_post_meta (create, checked right after the insert; a refusal deletes the new draft again) for their key; a refusal is a fields.<key> validation error. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01At3V6SjwbMe6eMzVGW3Hs7