Problem

getTableCellBorders only checked that a row had some parent node.

That let malformed trees treat any ancestor as the table, so the helper could invent top and left edge borders even when the cell was not actually inside a table.

Fix

• Resolve the row parent as before.
• Require the next ancestor to have the real table type before treating it as the table.
• Fall back to the default bottom and right borders when the table ancestor is missing or wrong.

Rule

Helpers that walk structural ancestors should validate node type, not just node existence.

Otherwise malformed trees quietly look valid and helper output lies.