test: keep the client suite independent of the host locale

src/components/SessionPicker.client.test.tsx

@@ -151,14 +151,16 @@ describe('SessionPicker', () => {
 
 describe('relativeTime', () => {
   const now = Date.parse('2026-09-17T12:00:00Z');
+  // The assertions match English wording.
+  const ago = (iso: string) => relativeTime(Date.parse(iso), now, 'en');
 
   it('picks the largest fitting unit', () => {
-    expect(relativeTime(Date.parse('2026-09-15T12:00:00Z'), now)).toMatch(/day/);
-    expect(relativeTime(Date.parse('2026-09-17T09:00:00Z'), now)).toMatch(/hour/);
-    expect(relativeTime(Date.parse('2026-09-17T11:30:00Z'), now)).toMatch(/minute/);
+    expect(ago('2026-09-15T12:00:00Z')).toMatch(/day/);
+    expect(ago('2026-09-17T09:00:00Z')).toMatch(/hour/);
+    expect(ago('2026-09-17T11:30:00Z')).toMatch(/minute/);
   });
 
   it('falls through to seconds for a very recent session', () => {
-    expect(relativeTime(Date.parse('2026-09-17T11:59:50Z'), now)).toMatch(/second/);
+    expect(ago('2026-09-17T11:59:50Z')).toMatch(/second/);
   });
 });

src/components/SessionPicker.tsx

@@ -6,9 +6,10 @@ import { canResumeSessionId } from '../../electron/shared/session-resume';
 import type { SessionRecord } from '../../electron/shared/session-record';
 
 /** Relative age of a session, via the platform formatter rather than a table
- *  of thresholds. Exported for its test. */
-export function relativeTime(epochMs: number, now = Date.now()): string {
-  const format = new Intl.RelativeTimeFormat(undefined, { numeric: 'auto' });
+ *  of thresholds. Exported for its test, which pins `locale` so the wording it
+ *  checks does not depend on the host's default. */
+export function relativeTime(epochMs: number, now = Date.now(), locale?: string): string {
+  const format = new Intl.RelativeTimeFormat(locale, { numeric: 'auto' });
   const seconds = Math.round((epochMs - now) / 1000);
   const units: [Intl.RelativeTimeFormatUnit, number][] = [
     ['day', 86_400],

src/components/chat/ContextMeter.client.test.tsx

@@ -22,12 +22,15 @@ afterEach(() => {
   container.remove();
 });
 
+// Exact counts are formatted in the host's locale, so the expected text is too.
+const n = (value: number) => value.toLocaleString();
+
 it('shows how full the context is, with exact figures and over-limit usage on hover', () => {
   expect(meter()).toBeNull();
   setState({ ...base, contextUsage: { usedTokens: 50000, maxTokens: 200000 } });
   // A ring alone until the window runs short; the figures wait on hover.
   expect(meter()?.textContent).toBe('');
-  expect(meter()?.title).toContain('50,000 of 200,000 tokens used, 150K left');
+  expect(meter()?.title).toContain(`${n(50_000)} of ${n(200_000)} tokens used, 150K left`);
   expect(meter()?.getAttribute('aria-valuenow')).toBe('50000');
   setState({ ...base, contextUsage: { usedTokens: 190000, maxTokens: 200000 } });
   expect(meter()?.dataset.level).toBe('high');
@@ -36,7 +39,7 @@ it('shows how full the context is, with exact figures and over-limit usage on ho
   expect(meter()?.textContent).toBe('105%');
   expect(meter()?.dataset.level).toBe('full');
   expect(meter()?.getAttribute('aria-valuenow')).toBe('200000');
-  expect(meter()?.getAttribute('aria-valuetext')).toContain('210,000 of 200,000');
+  expect(meter()?.getAttribute('aria-valuetext')).toContain(`${n(210_000)} of ${n(200_000)}`);
   setState(base);
   expect(meter()).toBeNull();
 });
@@ -55,7 +58,7 @@ it('adds the session token breakdown to the hover text', () => {
       scope: 'conversation',
     },
   });
-  expect(meter()?.title).toContain('Session: 12,500 tokens · 12,000 input');
+  expect(meter()?.title).toContain(`Session: ${n(12_500)} tokens · ${n(12_000)} input`);
   expect(meter()?.title).toContain('for this conversation');
   setState({
     ...base,