refactor(time): extract relativeTime into shared time.ts utility

Move relativeTime from notifications.ts (Intl.RelativeTimeFormat) to a
new time.ts that uses the Paraglide comment_time_* message keys — the
same logic that was already in CommentThread's timeAgo(). Remove the
duplicate timeAgo() from CommentThread and re-export relativeTime from
notifications.ts for backwards compatibility.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/lib/components/CommentThread.svelte

@@ -4,6 +4,7 @@ import { m } from '$lib/paraglide/messages.js';
 import type { Comment } from '$lib/types';
 import MentionEditor from '$lib/components/MentionEditor.svelte';
 import { renderBody, extractContent } from '$lib/utils/mention';
+import { relativeTime } from '$lib/utils/time';
 import type { MentionDTO } from '$lib/types';
 
 type Props = {
@@ -67,17 +68,6 @@ $effect(() => {
 	}
 });
 
-function timeAgo(iso: string): string {
-	const diff = Date.now() - new Date(iso).getTime();
-	const minutes = Math.floor(diff / 60000);
-	if (minutes < 1) return m.comment_time_just_now();
-	if (minutes < 60) return m.comment_time_minutes({ count: minutes });
-	const hours = Math.floor(minutes / 60);
-	if (hours < 24) return m.comment_time_hours({ count: hours });
-	const days = Math.floor(hours / 24);
-	return m.comment_time_days({ count: days });
-}
-
 function wasEdited(c: { createdAt: string; updatedAt: string }): boolean {
 	return c.updatedAt > c.createdAt;
 }
@@ -235,10 +225,10 @@ onMount(() => {
 							<span class="font-sans text-sm font-semibold text-ink">{msg.authorName}</span>
 							{#if wasEdited(msg)}
 								<span class="font-sans text-xs text-ink-3"
-									>{timeAgo(msg.updatedAt)} {m.comment_edited_label()}</span
+									>{relativeTime(msg.updatedAt)} {m.comment_edited_label()}</span
 								>
 							{:else}
-								<span class="font-sans text-xs text-ink-3">{timeAgo(msg.createdAt)}</span>
+								<span class="font-sans text-xs text-ink-3">{relativeTime(msg.createdAt)}</span>
 							{/if}
 						</div>
 						{#if parsed.quote}

frontend/src/lib/utils/notifications.spec.ts

@@ -1,56 +1,5 @@
 import { describe, it, expect } from 'vitest';
-import { relativeTime, parseNotificationEvent } from '$lib/utils/notifications';
-
-const rtf = new Intl.RelativeTimeFormat(undefined, { numeric: 'auto' });
-
-function msAgo(ms: number, now: Date): string {
-	return new Date(now.getTime() - ms).toISOString();
-}
-
-describe('relativeTime', () => {
-	const now = new Date('2024-06-15T12:00:00.000Z');
-
-	it('should use minute bucket for timestamps under 60 seconds ago', () => {
-		const ts = msAgo(30_000, now);
-		expect(relativeTime(ts, now)).toBe(rtf.format(0, 'minute'));
-	});
-
-	it('should use minute bucket for exactly 59 minutes ago', () => {
-		const ts = msAgo(59 * 60_000, now);
-		expect(relativeTime(ts, now)).toBe(rtf.format(-59, 'minute'));
-	});
-
-	it('should use minute bucket for exactly 1 minute ago', () => {
-		const ts = msAgo(60_000, now);
-		expect(relativeTime(ts, now)).toBe(rtf.format(-1, 'minute'));
-	});
-
-	it('should use hour bucket for exactly 1 hour ago', () => {
-		const ts = msAgo(60 * 60_000, now);
-		expect(relativeTime(ts, now)).toBe(rtf.format(-1, 'hour'));
-	});
-
-	it('should use hour bucket for 23 hours ago', () => {
-		const ts = msAgo(23 * 60 * 60_000, now);
-		expect(relativeTime(ts, now)).toBe(rtf.format(-23, 'hour'));
-	});
-
-	it('should use day bucket for exactly 24 hours ago', () => {
-		const ts = msAgo(24 * 60 * 60_000, now);
-		expect(relativeTime(ts, now)).toBe(rtf.format(-1, 'day'));
-	});
-
-	it('should use day bucket for 6 days ago', () => {
-		const ts = msAgo(6 * 24 * 60 * 60_000, now);
-		expect(relativeTime(ts, now)).toBe(rtf.format(-6, 'day'));
-	});
-
-	it('should default now to current time when omitted', () => {
-		// Just verify it returns a non-empty string — exact value depends on runtime clock
-		const ts = new Date(Date.now() - 5 * 60_000).toISOString();
-		expect(relativeTime(ts)).toBeTruthy();
-	});
-});
+import { parseNotificationEvent } from '$lib/utils/notifications';
 
 describe('parseNotificationEvent', () => {
 	const valid = {

frontend/src/lib/utils/notifications.ts

@@ -10,18 +10,7 @@ export type NotificationItem = {
 	documentTitle: string | null;
 };
 
-const rtf = new Intl.RelativeTimeFormat(undefined, { numeric: 'auto' });
-
-export function relativeTime(isoString: string, now: Date = new Date()): string {
-	const diffMs = now.getTime() - new Date(isoString).getTime();
-	const diffMin = Math.floor(diffMs / 60_000);
-	if (diffMin < 1) return rtf.format(0, 'minute');
-	if (diffMin < 60) return rtf.format(-diffMin, 'minute');
-	const diffH = Math.floor(diffMin / 60);
-	if (diffH < 24) return rtf.format(-diffH, 'hour');
-	const diffD = Math.floor(diffH / 24);
-	return rtf.format(-diffD, 'day');
-}
+export { relativeTime } from '$lib/utils/time';
 
 export function parseNotificationEvent(raw: string): NotificationItem | null {
 	try {

frontend/src/lib/utils/time.spec.ts

@@ -0,0 +1,52 @@
+import { describe, it, expect } from 'vitest';
+import { m } from '$lib/paraglide/messages.js';
+
+const { relativeTime } = await import('./time');
+
+function msAgo(ms: number, now: Date): string {
+	return new Date(now.getTime() - ms).toISOString();
+}
+
+describe('relativeTime', () => {
+	const now = new Date('2024-06-15T12:00:00.000Z');
+
+	it('returns "just now" for timestamps under 60 seconds ago', () => {
+		const ts = msAgo(30_000, now);
+		expect(relativeTime(ts, now)).toBe(m.comment_time_just_now());
+	});
+
+	it('returns 1-minute label for exactly 1 minute ago', () => {
+		const ts = msAgo(60_000, now);
+		expect(relativeTime(ts, now)).toBe(m.comment_time_minutes({ count: 1 }));
+	});
+
+	it('returns 59-minute label for exactly 59 minutes ago', () => {
+		const ts = msAgo(59 * 60_000, now);
+		expect(relativeTime(ts, now)).toBe(m.comment_time_minutes({ count: 59 }));
+	});
+
+	it('returns 1-hour label for exactly 1 hour ago', () => {
+		const ts = msAgo(60 * 60_000, now);
+		expect(relativeTime(ts, now)).toBe(m.comment_time_hours({ count: 1 }));
+	});
+
+	it('returns 23-hour label for 23 hours ago', () => {
+		const ts = msAgo(23 * 60 * 60_000, now);
+		expect(relativeTime(ts, now)).toBe(m.comment_time_hours({ count: 23 }));
+	});
+
+	it('returns 1-day label for exactly 24 hours ago', () => {
+		const ts = msAgo(24 * 60 * 60_000, now);
+		expect(relativeTime(ts, now)).toBe(m.comment_time_days({ count: 1 }));
+	});
+
+	it('returns 6-day label for 6 days ago', () => {
+		const ts = msAgo(6 * 24 * 60 * 60_000, now);
+		expect(relativeTime(ts, now)).toBe(m.comment_time_days({ count: 6 }));
+	});
+
+	it('defaults now to current time when omitted', () => {
+		const ts = new Date(Date.now() - 5 * 60_000).toISOString();
+		expect(relativeTime(ts)).toBeTruthy();
+	});
+});

frontend/src/lib/utils/time.ts

@@ -0,0 +1,12 @@
+import { m } from '$lib/paraglide/messages.js';
+
+export function relativeTime(isoString: string, now: Date = new Date()): string {
+	const diff = now.getTime() - new Date(isoString).getTime();
+	const minutes = Math.floor(diff / 60_000);
+	if (minutes < 1) return m.comment_time_just_now();
+	if (minutes < 60) return m.comment_time_minutes({ count: minutes });
+	const hours = Math.floor(minutes / 60);
+	if (hours < 24) return m.comment_time_hours({ count: hours });
+	const days = Math.floor(hours / 24);
+	return m.comment_time_days({ count: days });
+}