Detect and apply a summary-style split on one vault article: write the new
child article + the trimmed parent and commit. A NO-OP when no section
dominates ("no-candidate") or the structural split gate vetoes ("rejected").
Never clobbers an existing child article (that would be a MERGE, not a split).
Detect and apply a summary-style split on one vault article: write the new child article + the trimmed parent and commit. A NO-OP when no section dominates ("no-candidate") or the structural split gate vetoes ("rejected"). Never clobbers an existing child article (that would be a MERGE, not a split).