4930 Resolve PR feedback

Goal

Resolve new actionable review feedback on #4930 and close the corresponding PR thread without regressing the merged-cell border fix.

Source Of Truth

• GitHub PR: #4930 fix(table): resolve merged border neighbors
• Task type: PR feedback resolution
• Current actionable item count: 1

Feedback

1. packages/table/src/lib/queries/getAdjacentTableCell.ts:40 Reviewer concern: adjacent-cell lookups now linearly scan the full table on every top/left lookup, which can turn border operations into a quadratic hot path on large selections.

Phases

1. Fetch feedback and classify actionable items. Status: done
2. Evaluate the performance concern against the current helper/caller graph. Status: done
3. Implement the valid fix and targeted coverage. Status: done
4. Run relevant verification. Status: done
5. Reply, resolve, and re-fetch PR feedback. Status: done

Findings

• The unresolved thread is real and actionable; the other fetched comments are bot noise.
• getAdjacentTableCell currently calls findCellByIndexes, which flattens and scans the whole table each time.
• Callers like getSelectedCellBorderTargets and isSelectedCellBorder do these lookups inside per-cell loops, so the new merged-cell fix did introduce avoidable repeated table scans.

Verification

• Targeted table tests covering border toggles and adjacent-cell lookup
• Package build/typecheck/lint sequence for packages/table
• pnpm check
• Re-fetch PR comments after replying/resolving