feat(ui): show session cost in VS Code context usage readout (#2991)

Share the desktop session-card currency formatter (lib/money.ts) and surface
the current session's cost in the extension chat-header context usage tooltip.

packages/ui/src/components/layout/ContextSidebarTab.tsx

@@ -11,6 +11,7 @@ import { computeCacheHitRate } from '@/stores/utils/tokenUtils';
 import { useSessions, useSessionMessageRecords } from '@/sync/sync-context';
 import { copyTextToClipboard } from '@/lib/clipboard';
 import { getCurrentIntlLocale, useI18n } from '@/lib/i18n';
+import { formatMoney } from '@/lib/money';
 import {
   derivePartsLabel,
   deriveUserSnippet,
@@ -236,16 +237,6 @@ const computeContextBreakdown = (
 
 const formatNumber = (value: number): string => value.toLocaleString(getCurrentIntlLocale());
 
-const formatMoney = (value: number): string => {
-  if (!Number.isFinite(value) || value <= 0) return new Intl.NumberFormat(getCurrentIntlLocale(), { style: 'currency', currency: 'USD', minimumFractionDigits: 2, maximumFractionDigits: 2 }).format(0);
-  return new Intl.NumberFormat(getCurrentIntlLocale(), {
-    style: 'currency',
-    currency: 'USD',
-    minimumFractionDigits: value < 0.01 ? 4 : 2,
-    maximumFractionDigits: value < 0.01 ? 4 : 2,
-  }).format(value);
-};
-
 const formatDateTime = (timestamp: number | null, timeFormatPreference: TimeFormatPreference): string => {
   if (!timestamp || !Number.isFinite(timestamp)) return '-';
   return formatDateTimeForPreference(timestamp, timeFormatPreference, {

packages/ui/src/components/layout/VSCodeLayout.tsx

@@ -5,7 +5,7 @@ import { SessionDialogs } from '@/components/session/SessionDialogs';
 import { ChatView } from '@/components/views/ChatView';
 import { useSessionUIStore } from '@/sync/session-ui-store';
 import { useViewportStore } from '@/sync/viewport-store';
-import { useSessions, useDirectorySync, useSessionMessages, useSessionMessagesResolved } from '@/sync/sync-context';
+import { useSessions, useDirectorySync, useSession, useSessionMessages, useSessionMessagesResolved } from '@/sync/sync-context';
 import { useConfigStore } from '@/stores/useConfigStore';
 import { resolveGlobalSessionDirectory, useGlobalSessionsStore } from '@/stores/useGlobalSessionsStore';
 import { contextTokensFromBreakdown } from '@/stores/utils/tokenUtils';
@@ -666,6 +666,7 @@ const VSCodeHeader: React.FC<VSCodeHeaderProps> = ({ title, showBack, onBack, on
   const providers = useConfigStore((state) => state.providers);
   const currentSessionId = useSessionUIStore((state) => state.currentSessionId);
   const activeProjectId = useProjectsStore((state) => state.activeProjectId);
+  const currentSession = useSession(currentSessionId ?? '');
   const currentSessionMessages = useSessionMessages(currentSessionId ?? '');
   const currentSessionMessagesResolved = useSessionMessagesResolved(currentSessionId ?? '');
   const quotaResults = useQuotaStore((state) => state.results);
@@ -1022,6 +1023,7 @@ const VSCodeHeader: React.FC<VSCodeHeaderProps> = ({ title, showBack, onBack, on
           percentage={stableContextUsage.percentage}
           contextLimit={stableContextUsage.contextLimit}
           outputLimit={stableContextUsage.outputLimit ?? 0}
+          cost={(currentSession?.cost ?? 0) > 0 ? currentSession?.cost : null}
           className="h-9 shrink-0 pl-1 pr-1 typography-ui-label"
           valueClassName="font-semibold leading-none"
           hideIcon

packages/ui/src/components/ui/ContextUsageDisplay.tsx

@@ -4,6 +4,7 @@ import { Tooltip, TooltipContent, TooltipTrigger } from '@/components/ui/tooltip
 import { MobileOverlayPanel } from '@/components/ui/MobileOverlayPanel';
 import { Icon } from "@/components/icon/Icon";
 import { useI18n } from '@/lib/i18n';
+import { formatMoney } from '@/lib/money';
 import { clampPercent, resolveUsageTone } from '@/lib/quota';
 
 interface ContextUsageDisplayProps {
@@ -12,6 +13,7 @@ interface ContextUsageDisplayProps {
   colorPercentage?: number;
   contextLimit: number;
   outputLimit?: number;
+  cost?: number | null;
   size?: 'default' | 'compact';
   isMobile?: boolean;
   hideIcon?: boolean;
@@ -29,6 +31,7 @@ export const ContextUsageDisplay: React.FC<ContextUsageDisplayProps> = ({
   colorPercentage,
   contextLimit,
   outputLimit,
+  cost = null,
   size = 'default',
   isMobile = false,
   hideIcon = false,
@@ -73,10 +76,13 @@ export const ContextUsageDisplay: React.FC<ContextUsageDisplayProps> = ({
   const circularProgressOffset = circularProgressCircumference * (1 - progressPct / 100);
 
   const safeOutputLimit = typeof outputLimit === 'number' ? Math.max(outputLimit, 0) : 0;
+  const normalizedCost = cost ?? 0;
+  const hasCost = normalizedCost > 0 && Number.isFinite(normalizedCost);
   const tooltipLines = [
     t('contextUsage.tooltip.usedTokens', { tokens: formatTokens(totalTokens) }),
     t('contextUsage.tooltip.contextLimit', { tokens: formatTokens(contextLimit) }),
     t('contextUsage.tooltip.outputLimit', { tokens: formatTokens(safeOutputLimit) }),
+    ...(hasCost ? [t('contextUsage.tooltip.cost', { cost: formatMoney(normalizedCost) })] : []),
   ];
 
   const isInteractive = !isMobile && typeof onClick === 'function';
@@ -183,6 +189,12 @@ export const ContextUsageDisplay: React.FC<ContextUsageDisplayProps> = ({
                 <span className="typography-meta text-muted-foreground">{t('contextUsage.mobile.outputLimit')}</span>
                 <span className="typography-meta text-foreground font-medium">{formatTokens(safeOutputLimit)}</span>
               </div>
+              {hasCost ? (
+                <div className="flex justify-between items-center">
+                  <span className="typography-meta text-muted-foreground">{t('contextUsage.mobile.cost')}</span>
+                  <span className="typography-meta text-foreground font-medium">{formatMoney(normalizedCost)}</span>
+                </div>
+              ) : null}
               <div className="flex justify-between items-center pt-1 border-t border-border/40">
                 <span className="typography-meta text-muted-foreground">{t('contextUsage.mobile.usage')}</span>
                 <span className={cn('typography-meta font-semibold', getPercentageColor(colorPct))}>