fix expenses list performance + dom nesting

- memoize accordion cards and groupByMonth so toggling one
  expense re-renders O(1) cards instead of the whole list
- cache Intl.NumberFormat and date formatters per key (was
  ~2-3 instantiations per item per render)
- unmount collapsed accordion details via unmountOnExit to cut
  initial mount cost and input delay
- restructure Account row in ExpenseDetail so Chip is not nested
  inside <p> (fixes validateDOMNesting warning)
- avoid mutating expenses state array when sorting

src/Expense/Expense.tsx

@@ -54,7 +54,7 @@ export default function Expense() {
 
   const sorted = useMemo(
     () =>
-      (items ?? []).sort(
+      [...(items ?? [])].sort(
         (a, b) => new Date(b.occurred_at ?? 0).getTime() - new Date(a.occurred_at ?? 0).getTime(),
       ),
     [items],

src/Expense/ExpenseDetail.tsx

@@ -33,17 +33,19 @@ export function ExpenseDetail({ item }: { item: ExpenseItem }) {
       <Row
         label="Account"
         value={
-          <Typography variant="body2">
+          <Box sx={{ display: "flex", alignItems: "center", flexWrap: "wrap", gap: 1 }}>
+            <Typography component="span" variant="body2">
               {account ? `${account.name}${last4 ? ` (${last4})` : ""}` : "—"}
+            </Typography>
             {account?.type && (
               <Chip
                 size="small"
                 label={account.type.replace(/_/g, " ")}
                 variant="outlined"
-                sx={{ ml: 1.5, fontSize: 11, height: 20 }}
+                sx={{ fontSize: 11, height: 20 }}
               />
             )}
-          </Typography>
+          </Box>
         }
       />
       <Row

src/Expense/ExpenseList.tsx

@@ -1,7 +1,6 @@
-import React, { useState } from "react";
+import React, { useCallback, useMemo, useState } from "react";
 import {
   Box,
-  Paper,
   Typography,
   Accordion,
   AccordionSummary,
@@ -67,40 +66,26 @@ function EntityAvatar({ entity }: { entity: ExpenseItem["entity"] }) {
   );
 }
 
-export function ExpenseList({ items }: { items: ExpenseItem[] }) {
-  const [expandedId, setExpandedId] = useState<string | null>(null);
-  const groups = groupByMonth(items);
+interface ExpenseCardProps {
+  item: ExpenseItem;
+  expanded: boolean;
+  currency: string;
+  onToggle: (id: string) => void;
+}
 
-  return (
-    <Box sx={{ display: "flex", flexDirection: "column", gap: 4 }}>
-      {groups.map((group) => (
-        <Box key={group.key}>
-          <Box sx={{ display: "flex", alignItems: "baseline", gap: 1.5, mb: 1.5 }}>
-            <Typography variant="h6" fontWeight={700} sx={{ letterSpacing: "-0.01em" }}>
-              {monthLabel(group.key)}
-            </Typography>
-            <Typography variant="caption" color="text.secondary">
-              {group.items.length} transaction{group.items.length === 1 ? "" : "s"}
-            </Typography>
-            <Box sx={{ flex: 1 }} />
-            <Typography variant="body2" fontWeight={600}>
-              {formatCurrency(group.total, group.currency)}
-            </Typography>
-          </Box>
-
-          <Box sx={{ display: "flex", flexDirection: "column", gap: 1 }}>
-            {group.items.map((item) => {
+const ExpenseCard = React.memo(function ExpenseCard({ item, expanded, currency, onToggle }: ExpenseCardProps) {
   const negative = isExpense(item);
-              const currency = item.account?.currency ?? group.currency;
+  const itemCurrency = item.account?.currency ?? currency;
+
   return (
     <Accordion
-                  key={item.id}
       disableGutters
-                  expanded={expandedId === item.id}
-                  onChange={(_, expanded) => setExpandedId(expanded ? item.id : null)}
+      expanded={expanded}
+      onChange={(_, isExpanded) => onToggle(isExpanded ? item.id : "")}
+      TransitionProps={{ unmountOnExit: true }}
       sx={{
         border: "1px solid",
-                    borderColor: expandedId === item.id ? "primary.main" : "divider",
+        borderColor: expanded ? "primary.main" : "divider",
         borderRadius: 2,
         overflow: "hidden",
         boxShadow: "none",
@@ -154,7 +139,7 @@ export function ExpenseList({ items }: { items: ExpenseItem[] }) {
             flexShrink: 0,
           }}
         >
-                      {formatCurrency(item.amount, currency)}
+          {formatCurrency(item.amount, itemCurrency)}
         </Typography>
       </AccordionSummary>
       <AccordionDetails sx={{ pt: 0 }}>
@@ -162,7 +147,42 @@ export function ExpenseList({ items }: { items: ExpenseItem[] }) {
       </AccordionDetails>
     </Accordion>
   );
-            })}
+});
+
+export function ExpenseList({ items }: { items: ExpenseItem[] }) {
+  const [expandedId, setExpandedId] = useState<string | null>(null);
+  const groups = useMemo(() => groupByMonth(items), [items]);
+  const handleToggle = useCallback((id: string) => {
+    setExpandedId((prev) => (prev === id ? null : id));
+  }, []);
+
+  return (
+    <Box sx={{ display: "flex", flexDirection: "column", gap: 4 }}>
+      {groups.map((group) => (
+        <Box key={group.key}>
+          <Box sx={{ display: "flex", alignItems: "baseline", gap: 1.5, mb: 1.5 }}>
+            <Typography variant="h6" fontWeight={700} sx={{ letterSpacing: "-0.01em" }}>
+              {monthLabel(group.key)}
+            </Typography>
+            <Typography variant="caption" color="text.secondary">
+              {group.items.length} transaction{group.items.length === 1 ? "" : "s"}
+            </Typography>
+            <Box sx={{ flex: 1 }} />
+            <Typography variant="body2" fontWeight={600}>
+              {formatCurrency(group.total, group.currency)}
+            </Typography>
+          </Box>
+
+          <Box sx={{ display: "flex", flexDirection: "column", gap: 1 }}>
+            {group.items.map((item) => (
+              <ExpenseCard
+                key={item.id}
+                item={item}
+                expanded={expandedId === item.id}
+                currency={group.currency}
+                onToggle={handleToggle}
+              />
+            ))}
           </Box>
         </Box>
       ))}

src/Expense/types.ts

@@ -13,37 +13,53 @@ export function isExpense(item: ExpenseItem): boolean {
   return (item.amount ?? 0) < 0;
 }
 
+const CURRENCIES = ["INR", "USD", "EUR", "GBP", "AED", "SGD"];
+const _currencyFormatters = new Map<string, Intl.NumberFormat>();
+
 export function formatCurrency(amount: number, currency?: string): string {
-  const code = currency && ["INR", "USD", "EUR", "GBP", "AED", "SGD"].includes(currency) ? currency : "INR";
-  try {
-    return new Intl.NumberFormat("en-IN", {
+  const code = currency && CURRENCIES.includes(currency) ? currency : "INR";
+  let formatter = _currencyFormatters.get(code);
+  if (!formatter) {
+    formatter = new Intl.NumberFormat("en-IN", {
       style: "currency",
       currency: code,
       maximumFractionDigits: 2,
-    }).format(amount);
-  } catch {
-    return `₹${amount.toFixed(2)}`;
+    });
+    _currencyFormatters.set(code, formatter);
   }
+  return formatter.format(amount);
 }
 
+const _dateCache = new Map<string, string>();
+
 export function formatDate(iso?: string): string {
   if (!iso) return "—";
+  const cached = _dateCache.get(iso);
+  if (cached) return cached;
   const d = new Date(iso);
   if (Number.isNaN(d.getTime())) return "—";
-  return d.toLocaleDateString("en-IN", { day: "numeric", month: "short", year: "numeric" });
+  const out = d.toLocaleDateString("en-IN", { day: "numeric", month: "short", year: "numeric" });
+  _dateCache.set(iso, out);
+  return out;
 }
 
+const _dateTimeCache = new Map<string, string>();
+
 export function formatDateTime(iso?: string): string {
   if (!iso) return "—";
+  const cached = _dateTimeCache.get(iso);
+  if (cached) return cached;
   const d = new Date(iso);
   if (Number.isNaN(d.getTime())) return "—";
-  return d.toLocaleString("en-IN", {
+  const out = d.toLocaleString("en-IN", {
     day: "numeric",
     month: "short",
     year: "numeric",
     hour: "numeric",
     minute: "2-digit",
   });
+  _dateTimeCache.set(iso, out);
+  return out;
 }
 
 export function monthKey(iso?: string): string {