perf(search): memoize virtual row to cut flushSync reconcile cost

[sanjams2]

== Motivation ==

Scroll on the search results table produces 90-450ms long tasks per tick

== Details ==

@tanstack/react-virtual calls flushSync(rerender) on every scroll event while isScrolling is true (see the onChange adapter in the react-virtual source). With overscan: 30 we keep ~90 rows mounted, and the inline items.map() render means React has no way to skip unchanged rows - it reconciles all 90 synchronously on every scroll notification, even when only 2-3 actually entered or left the window.

The comparator keys on row.id (tanstack-table's stable identifier) rather than object identity, since getRowModel() may return fresh row references even when data is unchanged. isHighlighted and isExpanded are computed per-row in the parent so that selecting one row doesn't bust memo on the other 89.

== Testing ==

• npx jest DBRowTable.test.tsx - 15/15 pass
• DevTools Performance profile on search page: hot path was scroll -> maybeNotify -> notify -> onChange -> flushSync -> React reconciler; memoizing the row lets React bail out on unchanged ones

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[github-actions]

PR Review

• ⚠️ Column resizing will silently break: The custom memo comparator only checks columnsLength but not column widths. When a user resizes a column, row.id and columnsLength stay the same, so all 90 memoized rows skip re-render — displaying stale widths. The comparator needs to include column sizes: either pass a columnSizing snapshot as a prop (e.g., columnSizingHash) and compare it, or add prev.row === next.row (object identity) to catch TanStack Table rebuilding row objects on state change.

• ⚠️ renderRowDetails excluded from comparator: If the parent passes a new renderRowDetails reference (e.g., due to re-render of a parent component), expanded rows won't update. Either add prev.renderRowDetails === next.renderRowDetails to the comparator or wrap renderRowDetails in useCallback at the call site.

• ✅ onRowExpandClick and onToggleWrap are properly stabilized with useCallback — no stale closure risk there.

[github-actions]

🟡 Tier 3 — Standard

Introduces new logic, modifies core functionality, or touches areas with non-trivial risk.

Why this tier:

• Standard feature/fix — introduces new logic or modifies core functionality

Review process: Full human review — logic, architecture, edge cases.
SLA: First-pass feedback within 1 business day.

Stats

• Files changed: 1
• Lines changed: 313
• Branch: perf/memoize-virtual-row
• Author: sanjams2

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