diff --git a/.jules/bolt.md b/.jules/bolt.md
new file mode 100644
index 00000000..1480ede4
--- /dev/null
+++ b/.jules/bolt.md
@@ -0,0 +1,6 @@
+## 2024-05-18 - [Recharts Optimization]
+**Learning:** In Next.js components utilizing Recharts, transforming props data into chart-ready data points directly in the component body can cause significant performance bottlenecks due to expensive unnecessary recalculations on every React re-render. Some components have `useMemo` optimizations, but others are missing them.
+**Action:** Always wrap data transformation logic (e.g., mapping arrays or reducing data arrays) within `useMemo` hooks before passing the result to Recharts components.
+## 2024-05-18 - [EventList Rendering Optimization]
+**Learning:** In a virtualized list component (e.g., `react-window` List), if a function executed on every row calculates a value based on a parent's constant prop (e.g., parsing a `Date` string), it creates a severe performance bottleneck during scrolling due to redundant string parsing on every render cycle.
+**Action:** Always parse constant date strings or pre-calculate expensive parent-level constants using `useMemo` at the top level of the component and pass the computed primitive value (e.g., timestamp in milliseconds) down to the virtualized rows to eliminate repeated processing.
diff --git a/packages/web/src/components/dashboard/event-list.tsx b/packages/web/src/components/dashboard/event-list.tsx
index a3e4406c..487d31e3 100644
--- a/packages/web/src/components/dashboard/event-list.tsx
+++ b/packages/web/src/components/dashboard/event-list.tsx
@@ -39,9 +39,9 @@ type FlatRow =
 
 const ROW_HEIGHT = 36;
 
-function formatElapsed(timestamp: string, sessionStartedAt: string): string {
+function formatElapsed(timestamp: string, sessionStartMs: number): string {
   const t = new Date(timestamp).getTime();
-  const start = new Date(sessionStartedAt).getTime();
+  const start = sessionStartMs;
   if (Number.isNaN(t) || Number.isNaN(start)) return "";
   const diffSec = Math.max(0, Math.floor((t - start) / 1000));
   const h = Math.floor(diffSec / 3600);
@@ -207,7 +207,7 @@ function RowView({
 type RowProps = {
   rows: FlatRow[];
   selectedIdx: number;
-  sessionStartedAt: string;
+  sessionStartMs: number;
   onSelect: (idx: number) => void;
   onToggleGroup: (firstIdx: number) => void;
 };
@@ -217,7 +217,7 @@ function Row({
   style,
   rows,
   selectedIdx,
-  sessionStartedAt,
+  sessionStartMs,
   onSelect,
   onToggleGroup,
 }: RowComponentProps<RowProps>) {
@@ -230,7 +230,7 @@ function Row({
         <RowView
           label="Tool"
           preview={`${row.toolName} x${row.count}`}
-          time={formatElapsed(row.firstEvent.timestamp, sessionStartedAt)}
+          time={formatElapsed(row.firstEvent.timestamp, sessionStartMs)}
           icon={getIcon(row.firstEvent)}
           isSelected={false}
           onClick={() => onToggleGroup(row.groupFirstIdx)}
@@ -252,7 +252,7 @@ function Row({
       <RowView
         label={label}
         preview={preview}
-        time={formatElapsed(row.event.timestamp, sessionStartedAt)}
+        time={formatElapsed(row.event.timestamp, sessionStartMs)}
         icon={getIcon(row.event)}
         isSelected={row.idx === selectedIdx}
         onClick={() => onSelect(row.idx)}
@@ -271,6 +271,8 @@ export function EventList({
   expandedGroups,
   onToggleGroup,
 }: EventListProps) {
+  const sessionStartMs = useMemo(() => new Date(sessionStartedAt).getTime(), [sessionStartedAt]);
+
   const rows = useMemo(
     () => buildFlatRows(groups, expandedGroups, selectedIdx),
     [groups, expandedGroups, selectedIdx],
@@ -292,7 +294,7 @@ export function EventList({
       rowProps={{
         rows,
         selectedIdx,
-        sessionStartedAt,
+        sessionStartMs,
         onSelect,
         onToggleGroup,
       }}