Table cell helper queries must guard missing table ancestors

Problem

Direct helper coverage for getTableCellBorders(...) and getTableCellSize(...) exposed a bad assumption in the table query layer.

If a td node existed outside a full table > tr > td chain, both helpers could throw while walking parent entries instead of falling back safely.

Root Cause

Both helpers assumed that once a cell parent existed, the next parent lookup would always return a real table row or table node.

That is fine for ideal editor state, but too brittle for direct helper use, partial trees, or malformed intermediate structures.

Solution

Guard the parent lookups before reading row or table data.

For getTableCellBorders(...):

• if the row parent is missing, return default bottom/right borders
• if the table parent is missing, return the same safe fallback

For getTableCellSize(...):

• if the cell does not have a real tr parent, return { minHeight: 0, width: 0 }
• if the row exists but the table does not, keep the resolved row height and return width 0

Prevention

• Keep one direct helper spec for table query utilities, not only transform-level coverage.
• Any helper that climbs cell -> row -> table should treat each step as optional unless the function contract explicitly says malformed trees are invalid.
• When the fallback behavior is cheap and deterministic, prefer guarding over crashing.