diff --git a/.Jules/palette.md b/.Jules/palette.md
new file mode 100644
index 00000000..b5ac773f
--- /dev/null
+++ b/.Jules/palette.md
@@ -0,0 +1,3 @@
+## 2024-06-22 - Overview Stats 토글 버튼 키보드 접근성 개선
+**Learning:** `overview-stats` 컴포넌트의 설명 텍스트를 펼치거나 접는 `<button>` 요소에 키보드 포커스 스타일이 누락되어 있어, 키보드 내비게이션 사용자에게 현재 포커스 위치를 명확히 보여주지 못했습니다. `hover` 스타일은 있었으나 `focus-visible` 처리가 없어 접근성 결함이 있었습니다.
+**Action:** Tailwind CSS의 `focus-visible` 관련 유틸리티 클래스(`focus-visible:outline-none`, `focus-visible:ring-2`, `focus-visible:ring-ring`, `rounded-sm`)를 추가하여 탭(Tab) 키 이동 시 포커스 링이 보이도록 수정했습니다. 앞으로 대화형 컴포넌트를 설계할 때는 항상 키보드 접근성(focus states)을 염두에 두고 작업해야 합니다.
\ No newline at end of file
diff --git a/CHANGELOG.md b/CHANGELOG.md
new file mode 100644
index 00000000..53cd4221
--- /dev/null
+++ b/CHANGELOG.md
@@ -0,0 +1,7 @@
+# Changelog
+
+## [Unreleased]
+
+### 🎨 변경 사항 (UX / 접근성)
+
+- 웹 대시보드의 각종 로그아웃 버튼(`org-sidebar.tsx`, `org-header.tsx`, `no-organization-state.tsx`)에 스크린 리더용 `aria-label="Log out of your account"` (또는 `Sign out of your account`) 속성을 추가하여 접근성을 개선했습니다.
diff --git a/packages/web/src/app/dashboard/[orgSlug]/sessions/[sessionId]/page.tsx b/packages/web/src/app/dashboard/[orgSlug]/sessions/[sessionId]/page.tsx
index 1bea6e3e..4477ad5b 100644
--- a/packages/web/src/app/dashboard/[orgSlug]/sessions/[sessionId]/page.tsx
+++ b/packages/web/src/app/dashboard/[orgSlug]/sessions/[sessionId]/page.tsx
@@ -13,7 +13,7 @@ import {
   SessionFilesTab,
 } from '@/components/dashboard/session-files'
 import { useSessionDetail } from '@/hooks/use-dashboard-sessions'
-import { messagesToTimeline, formatSlashCommandText } from '@/lib/timeline-events'
+import { messagesToTimeline, buildTimelineGroups, formatSlashCommandText } from '@/lib/timeline-events'
 import { extractSessionFiles } from '@/lib/session-files'
 import {
   formatTokens,
@@ -46,6 +46,7 @@ export default function OrgSessionDetailPage({
     () => (data ? messagesToTimeline(data.messages) : []),
     [data],
   )
+  const groups = useMemo(() => buildTimelineGroups(events), [events])
   const files = useMemo(() => extractSessionFiles(events), [events])
   const [selectedIdx, setSelectedIdx] = useState<number | null>(0)
   const safeIdx =
@@ -221,6 +222,7 @@ export default function OrgSessionDetailPage({
             <div className="px-4 pt-3 pb-2">
               <SessionActivityRibbon
                 events={events}
+                groups={groups}
                 selectedIdx={safeIdx}
                 onSelect={setSelectedIdx}
                 sessionStartedAt={data.startedAt}
@@ -232,6 +234,7 @@ export default function OrgSessionDetailPage({
               <div className="border-r border-border min-h-0 overflow-hidden">
                 <EventList
                   events={events}
+                  groups={groups}
                   selectedIdx={safeIdx ?? -1}
                   onSelect={setSelectedIdx}
                   sessionStartedAt={data.startedAt}
diff --git a/packages/web/src/components/dashboard/event-list.tsx b/packages/web/src/components/dashboard/event-list.tsx
index 61a3f686..fe1c9bdd 100644
--- a/packages/web/src/components/dashboard/event-list.tsx
+++ b/packages/web/src/components/dashboard/event-list.tsx
@@ -3,13 +3,14 @@ import { List, type RowComponentProps } from "react-window";
 import { User, Bot, Wrench, ChevronRight } from "lucide-react";
 import {
   formatSlashCommandText,
-  buildTimelineGroups,
   type TimelineEvent,
+  type TimelineGroup,
 } from "@/lib/timeline-events";
 import { cn } from "@/lib/utils";
 
 type EventListProps = {
   events: TimelineEvent[];
+  groups: TimelineGroup[];
   selectedIdx: number;
   onSelect: (idx: number) => void;
   sessionStartedAt: string;
@@ -50,11 +51,10 @@ function formatElapsed(timestamp: string, sessionStartedAt: string): string {
 }
 
 function buildFlatRows(
-  events: TimelineEvent[],
+  groups: TimelineGroup[],
   expandedGroups: Set<number>,
   selectedIdx: number,
 ): FlatRow[] {
-  const groups = buildTimelineGroups(events);
   const rows: FlatRow[] = [];
   for (const group of groups) {
     if (group.kind === "single") {
@@ -261,6 +261,7 @@ function Row({
 
 export function EventList({
   events,
+  groups,
   selectedIdx,
   onSelect,
   sessionStartedAt,
@@ -268,8 +269,8 @@ export function EventList({
   onToggleGroup,
 }: EventListProps) {
   const rows = useMemo(
-    () => buildFlatRows(events, expandedGroups, selectedIdx),
-    [events, expandedGroups, selectedIdx],
+    () => buildFlatRows(groups, expandedGroups, selectedIdx),
+    [groups, expandedGroups, selectedIdx],
   );
 
   if (events.length === 0) {
diff --git a/packages/web/src/components/dashboard/no-organization-state.tsx b/packages/web/src/components/dashboard/no-organization-state.tsx
index 43400ab0..95cd41dd 100644
--- a/packages/web/src/components/dashboard/no-organization-state.tsx
+++ b/packages/web/src/components/dashboard/no-organization-state.tsx
@@ -37,6 +37,7 @@ export function NoOrganizationState({
             <button
               onClick={() => signOut({ callbackUrl: '/login' })}
               className="text-sm text-destructive hover:underline"
+              aria-label="Log out of your account"
             >
               Log out
             </button>
diff --git a/packages/web/src/components/dashboard/overview-stats.tsx b/packages/web/src/components/dashboard/overview-stats.tsx
index 7b30abd7..db5b15de 100644
--- a/packages/web/src/components/dashboard/overview-stats.tsx
+++ b/packages/web/src/components/dashboard/overview-stats.tsx
@@ -88,7 +88,7 @@ export function OverviewStats({
         id="overview-stats-explanation-toggle"
         aria-expanded={expanded}
         aria-controls="overview-stats-explanation"
-        className="mt-4 flex items-center gap-2 text-xs text-muted-foreground hover:text-foreground transition-colors"
+        className="mt-4 flex items-center gap-2 text-xs text-muted-foreground hover:text-foreground focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring transition-colors rounded-sm"
       >
         <span
           aria-hidden="true"
diff --git a/packages/web/src/components/dashboard/reports/weekly-flow-chart.tsx b/packages/web/src/components/dashboard/reports/weekly-flow-chart.tsx
index 48b40ef7..96332537 100644
--- a/packages/web/src/components/dashboard/reports/weekly-flow-chart.tsx
+++ b/packages/web/src/components/dashboard/reports/weekly-flow-chart.tsx
@@ -12,6 +12,7 @@ import {
   Legend,
   type TooltipProps,
 } from 'recharts'
+import { useMemo } from 'react'
 import { parseISO } from 'date-fns'
 import { formatTokens } from '@/lib/format'
 import type { DailySeriesPoint } from '@/types/reports'
@@ -57,18 +58,22 @@ function sumTokens(p: DailySeriesPoint): number {
 }
 
 export function WeeklyFlowChart({ thisWeek, prevWeek }: WeeklyFlowChartProps) {
-  // 요일 기준으로 병합 (월~일 7개 슬롯)
-  const dayNames = ['Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun']
-  const data: ChartRow[] = dayNames.map((day) => ({ day, thisWeekTokens: 0, prevWeekTokens: 0 }))
+  const data = useMemo(() => {
+    // 요일 기준으로 병합 (월~일 7개 슬롯)
+    const dayNames = ['Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun']
+    const result: ChartRow[] = dayNames.map((day) => ({ day, thisWeekTokens: 0, prevWeekTokens: 0 }))
 
-  for (const p of thisWeek) {
-    const idx = dayIndex(p.date)
-    if (idx >= 0) data[idx].thisWeekTokens += sumTokens(p)
-  }
-  for (const p of prevWeek) {
-    const idx = dayIndex(p.date)
-    if (idx >= 0) data[idx].prevWeekTokens += sumTokens(p)
-  }
+    for (const p of thisWeek) {
+      const idx = dayIndex(p.date)
+      if (idx >= 0) result[idx].thisWeekTokens += sumTokens(p)
+    }
+    for (const p of prevWeek) {
+      const idx = dayIndex(p.date)
+      if (idx >= 0) result[idx].prevWeekTokens += sumTokens(p)
+    }
+
+    return result
+  }, [thisWeek, prevWeek])
 
   return (
     <ResponsiveContainer width="100%" height={260}>
diff --git a/packages/web/src/components/dashboard/session-activity-ribbon.tsx b/packages/web/src/components/dashboard/session-activity-ribbon.tsx
index 87a305ea..694e3806 100644
--- a/packages/web/src/components/dashboard/session-activity-ribbon.tsx
+++ b/packages/web/src/components/dashboard/session-activity-ribbon.tsx
@@ -1,16 +1,17 @@
 'use client'
 
-import { useMemo, useState, useRef } from 'react'
+import { useState, useRef } from 'react'
 import {
   formatSlashCommandText,
-  buildTimelineGroups,
   type TimelineEvent,
+  type TimelineGroup,
 } from '@/lib/timeline-events'
 import { formatTokens, formatCost, formatRelativeTime } from '@/lib/format'
 import { segmentVisuals } from './session-ribbon-visuals'
 
 type Props = {
   events: TimelineEvent[]
+  groups: TimelineGroup[]
   selectedIdx: number | null
   onSelect: (idx: number) => void
   sessionStartedAt: string
@@ -147,6 +148,7 @@ function MergedTooltipBody({
 
 export function SessionActivityRibbon({
   events,
+  groups,
   selectedIdx,
   onSelect,
   sessionStartedAt,
@@ -156,8 +158,6 @@ export function SessionActivityRibbon({
   const [hover, setHover] = useState<HoverState | null>(null)
   const containerRef = useRef<HTMLDivElement>(null)
 
-  const groups = useMemo(() => buildTimelineGroups(events), [events])
-
   if (events.length === 0) return null
 
   const trackMouse = (e: React.MouseEvent) => {
diff --git a/packages/web/src/components/dashboard/session-timeline-chart.tsx b/packages/web/src/components/dashboard/session-timeline-chart.tsx
index 4c6844f4..d0c657f0 100644
--- a/packages/web/src/components/dashboard/session-timeline-chart.tsx
+++ b/packages/web/src/components/dashboard/session-timeline-chart.tsx
@@ -24,6 +24,11 @@ interface ToolCallPoint {
   toolName: string
 }
 
+interface ParsedToolCallPoint {
+  timestampMs: number
+  toolName: string
+}
+
 interface ChartDataItem {
   relativeTime: string
   input: number
@@ -35,20 +40,18 @@ interface ChartDataItem {
 
 function getToolSummaryForIndex(
   index: number,
-  usageTimeline: SessionTimelineUsage[],
-  toolCalls: ToolCallPoint[]
+  parsedUsage: number[],
+  toolCalls: ParsedToolCallPoint[]
 ): string {
   if (toolCalls.length === 0) return ''
 
-  const currentTimestamp = new Date(usageTimeline[index]!.timestamp).getTime()
-  const prevTimestamp =
-    index > 0 ? new Date(usageTimeline[index - 1]!.timestamp).getTime() : 0
+  const currentTimestamp = parsedUsage[index]!
+  const prevTimestamp = index > 0 ? parsedUsage[index - 1]! : 0
 
   // 현재 usageTimeline timestamp 이전이면서, 이전 usageTimeline timestamp 이후의 tool events 찾기
   // 첫 번째 bar(index=0)는 prevTimestamp가 0이므로 해당 bar 이전의 모든 이벤트를 포함
   const relevantTools = toolCalls.filter((e) => {
-    const toolTimestamp = new Date(e.timestamp).getTime()
-    return toolTimestamp <= currentTimestamp && toolTimestamp > prevTimestamp
+    return e.timestampMs <= currentTimestamp && e.timestampMs > prevTimestamp
   })
 
   if (relevantTools.length === 0) return ''
@@ -132,9 +135,12 @@ export function SessionTimelineChart({
     )
   }
 
-  const toolCalls: ToolCallPoint[] = messages
+  // Pre-parse timestamps to avoid O(N*M) Date parsing inside loops
+  const toolCalls: ParsedToolCallPoint[] = messages
     .filter((m) => m.role === 'TOOL')
-    .map((m) => ({ timestamp: m.timestamp, toolName: m.toolName ?? 'unknown' }))
+    .map((m) => ({ timestampMs: new Date(m.timestamp).getTime(), toolName: m.toolName ?? 'unknown' }))
+
+  const parsedUsage = usageTimeline.map(u => new Date(u.timestamp).getTime())
 
   const chartData: ChartDataItem[] = usageTimeline.map((u, idx) => ({
     relativeTime: formatRelativeTime(u.timestamp, sessionStartedAt),
@@ -142,7 +148,7 @@ export function SessionTimelineChart({
     output: u.outputTokens,
     cost: u.estimatedCostUsd,
     model: u.model,
-    toolSummary: getToolSummaryForIndex(idx, usageTimeline, toolCalls),
+    toolSummary: getToolSummaryForIndex(idx, parsedUsage, toolCalls),
   }))
 
   return (
diff --git a/packages/web/src/components/dashboard/token-usage-chart.tsx b/packages/web/src/components/dashboard/token-usage-chart.tsx
index 3a076197..a9886e1b 100644
--- a/packages/web/src/components/dashboard/token-usage-chart.tsx
+++ b/packages/web/src/components/dashboard/token-usage-chart.tsx
@@ -1,5 +1,6 @@
 'use client'
 
+import { useMemo } from 'react'
 import { AreaChart, Area, XAxis, YAxis, CartesianGrid, Tooltip, ResponsiveContainer, TooltipProps } from 'recharts'
 import { formatTokens, formatCost } from '@/lib/format'
 import type { UsageSeries } from '@argos/shared'
@@ -43,15 +44,17 @@ function CustomTooltip({ active, payload, label }: TooltipProps<number, string>)
 }
 
 export function TokenUsageChart({ data }: TokenUsageChartProps) {
-  const chartData = data.map(d => {
-    const date = new Date(d.date)
-    return {
-      date: format(date, 'MMM d'),
-      fullDate: format(date, 'MMM d, yyyy'),
-      input: d.inputTokens,
-      output: d.outputTokens,
-    }
-  })
+  const chartData = useMemo(() => {
+    return data.map(d => {
+      const date = new Date(d.date)
+      return {
+        date: format(date, 'MMM d'),
+        fullDate: format(date, 'MMM d, yyyy'),
+        input: d.inputTokens,
+        output: d.outputTokens,
+      }
+    })
+  }, [data])
 
   return (
     <ResponsiveContainer width="100%" height={300}>
diff --git a/packages/web/src/components/layout/org-header.tsx b/packages/web/src/components/layout/org-header.tsx
index c33de1fc..7f57f267 100644
--- a/packages/web/src/components/layout/org-header.tsx
+++ b/packages/web/src/components/layout/org-header.tsx
@@ -18,6 +18,7 @@ export function OrgHeader({ orgName }: { orgName?: string }) {
           <Button
             variant="outline"
             onClick={() => signOut({ callbackUrl: '/login' })}
+            aria-label="Sign out of your account"
           >
             Sign out
           </Button>
diff --git a/packages/web/src/components/layout/org-sidebar.tsx b/packages/web/src/components/layout/org-sidebar.tsx
index 7f28d8d0..6d37e315 100644
--- a/packages/web/src/components/layout/org-sidebar.tsx
+++ b/packages/web/src/components/layout/org-sidebar.tsx
@@ -124,6 +124,7 @@ export function OrgSidebar() {
           <button
             onClick={handleLogout}
             className="w-full px-3 py-2 text-sm font-medium text-destructive hover:bg-destructive/10 rounded-md transition-colors"
+            aria-label="Log out of your account"
           >
             Log Out
           </button>
@@ -150,6 +151,7 @@ export function OrgSidebar() {
           <button
             onClick={handleLogout}
             className="px-3 py-1 text-sm text-destructive hover:bg-destructive/10 rounded-md transition-colors"
+            aria-label="Log out of your account"
           >
             Logout
           </button>
diff --git a/packages/web/src/lib/server/weekly-report.ts b/packages/web/src/lib/server/weekly-report.ts
index 7eabddbd..eb95d36f 100644
--- a/packages/web/src/lib/server/weekly-report.ts
+++ b/packages/web/src/lib/server/weekly-report.ts
@@ -392,17 +392,22 @@ export async function getWeeklyReport(
   }
 
   // Insights — delegation
-  const totalAgentCalls = thisWeekRollups.reduce(
-    (sum, r) => sum + Object.values(r.agentCounts).reduce((a, b) => a + b, 0),
-    0,
-  )
-  const totalSkillCalls = thisWeekRollups.reduce(
-    (sum, r) => sum + Object.values(r.skillCounts).reduce((a, b) => a + b, 0),
-    0,
-  )
+  // ⚡ Bolt Optimization:
+  // 병목 지점: 기존 코드는 `thisWeekRollups`를 3번 순회하고, 매 순회마다 Object.values()로 중간 배열을 생성하여 메모리 할당 비용이 발생했습니다.
+  // 최적화 방법: 단일 for...of 루프와 Object.keys() 순회를 결합하여 N+1 순회를 1회 순회로 통합하고 중간 배열 할당을 제거했습니다.
+  // 기대 효과: `thisWeekRollups`의 크기가 클 경우, 불필요한 배열 생성 오버헤드와 O(N) 순회를 1/3로 줄여 리포트 생성 성능이 향상됩니다.
+  let totalAgentCalls = 0
+  let totalSkillCalls = 0
   const distinctSkillsThisWeek = new Set<string>()
+
   for (const r of thisWeekRollups) {
-    for (const k of Object.keys(r.skillCounts)) distinctSkillsThisWeek.add(k)
+    for (const k of Object.keys(r.agentCounts)) {
+      totalAgentCalls += r.agentCounts[k]
+    }
+    for (const k of Object.keys(r.skillCounts)) {
+      totalSkillCalls += r.skillCounts[k]
+      distinctSkillsThisWeek.add(k)
+    }
   }
 
   const insights: WeeklyInsights = {