feat(acp): show relative last-activity time on chat history rows (#668)

* feat(acp): show relative last-activity time on chat history rows

Replace the bare message-count number on ACP chat-history rows with a
compact relative-time string (e.g. '3h', '2d', '5w') derived from the
lastActivityAt timestamp each row already carries. Both chat-history
surfaces — the sidebar ChatHistoryTab and the per-project ProjectChatList
— already sorted newest-first; only the display changed.

Reuses the existing git-time formatter by adding a number-based core
(formatRelativeTimeFromMs) that the ISO-string formatRelativeTime now
delegates to, preserving the git panel's API and tests exactly.

* docs(acp): add docstrings to ChatHistoryEntryRow and ProjectChatRow

Clears CodeRabbit's docstring-coverage pre-merge warning (50% → 100%
on the touched functions) by adding concise JSDoc to the two previously
undocumented row components.

Author: gnoviawan

src/renderer/components/ProjectChatList.tsx

@@ -12,6 +12,7 @@ import {
   ContextMenuTrigger
 } from '@/components/ui/context-menu'
 import { clipboardApi, openerApi } from '@/lib/api'
+import { formatRelativeTimeFromMs } from '@/lib/git-time'
 import { openTerminalAtCwd } from '@/lib/terminal-spawn'
 import { cn } from '@/lib/utils'
 import { useAcpStore, useAgentIcon, useAgentTemplateId } from '@/stores/acp-store'
@@ -288,7 +289,10 @@ interface ProjectChatRowProps {
   onCopyPath: (cwd: string) => void
   onDelete: (entry: ProjectChatEntry) => void
 }
-
+/**
+ * A single per-project chat row: title + relative last-activity time, with a
+ * context menu (open terminal / file explorer / copy path / delete).
+ */
 function ProjectChatRow({
   entry,
   onOpen,
@@ -315,7 +319,9 @@ function ProjectChatRow({
           >
             <ChatRowIcon agentId={entry.agentId} agentConfigId={entry.agentConfigId} />
             <span className="truncate flex-1 text-sidebar-foreground">{entry.title}</span>
-            <span className="text-3xs text-muted-foreground">{entry.messageCount}</span>
+            <span className="text-3xs text-muted-foreground">
+              {formatRelativeTimeFromMs(entry.lastActivityAt)}
+            </span>
           </button>
           <button
             type="button"

src/renderer/components/chat/ChatHistoryEntryRow.tsx

@@ -1,4 +1,5 @@
 import { Trash2 } from 'lucide-react'
+import { formatRelativeTimeFromMs } from '@/lib/git-time'
 import { cn } from '@/lib/utils'
 import { useAgentIcon, useAgentTemplateId } from '@/stores/acp-store'
 import { AgentGlyph } from './AgentGlyph'
@@ -37,7 +38,10 @@ interface ChatHistoryEntryRowProps {
   onOpen: (entry: ChatHistorySidebarEntry) => void
   onDelete: (id: string) => void
 }
-
+/**
+ * A single chat-history row for the sidebar `ChatHistoryTab`: agent icon, title,
+ * and a compact relative last-activity time (replacing the old message count).
+ */
 export function ChatHistoryEntryRow({
   entry,
   onOpen,
@@ -71,7 +75,9 @@ export function ChatHistoryEntryRow({
             <span className="text-3xs text-muted-foreground/70 shrink-0">{entry.agentName}</span>
           ) : null
         ) : (
-          <span className="text-3xs text-muted-foreground">{entry.messageCount}</span>
+          <span className="text-3xs text-muted-foreground">
+            {formatRelativeTimeFromMs(entry.lastActivityAt)}
+          </span>
         )}
       </button>
       {!entry.discovered && (

src/renderer/lib/git-time.test.ts

@@ -1,5 +1,5 @@
 import { describe, expect, it } from 'vitest'
-import { formatRelativeTime } from './git-time'
+import { formatRelativeTime, formatRelativeTimeFromMs } from './git-time'
 
 describe('formatRelativeTime', () => {
   const now = Date.parse('2026-05-30T12:00:00Z')
@@ -31,3 +31,29 @@ describe('formatRelativeTime', () => {
     expect(result).not.toMatch(/^\d+[mhdw]$/)
   })
 })
+
+describe('formatRelativeTimeFromMs', () => {
+  const now = Date.parse('2026-05-30T12:00:00Z')
+
+  it('returns empty string for non-finite input (NaN/Infinity)', () => {
+    expect(formatRelativeTimeFromMs(Number.NaN, now)).toBe('')
+    expect(formatRelativeTimeFromMs(Number.POSITIVE_INFINITY, now)).toBe('')
+  })
+
+  it('matches formatRelativeTime for the same instant', () => {
+    const iso = '2026-05-30T09:00:00Z'
+    expect(formatRelativeTimeFromMs(Date.parse(iso), now)).toBe(formatRelativeTime(iso, now))
+  })
+
+  it("formats sub-minute as 'now' and clamps future timestamps to 'now'", () => {
+    expect(formatRelativeTimeFromMs(now - 30_000, now)).toBe('now')
+    expect(formatRelativeTimeFromMs(now + 60_000, now)).toBe('now')
+  })
+
+  it('formats minutes, hours, days, and weeks', () => {
+    expect(formatRelativeTimeFromMs(now - 5 * 60_000, now)).toBe('5m')
+    expect(formatRelativeTimeFromMs(now - 3 * 3_600_000, now)).toBe('3h')
+    expect(formatRelativeTimeFromMs(now - 2 * 86_400_000, now)).toBe('2d')
+    expect(formatRelativeTimeFromMs(now - 14 * 86_400_000, now)).toBe('2w')
+  })
+})

src/renderer/lib/git-time.ts

@@ -1,16 +1,17 @@
 /**
- * Format an ISO 8601 timestamp as a compact relative time for commit rows,
- * e.g. "now", "5m", "3h", "2d", "5w". Falls back to a short localized date for
- * anything older than ~8 weeks. Invalid input yields an empty string so the UI
- * can render nothing rather than "Invalid Date".
+ * Format an epoch-millisecond timestamp as a compact relative time, e.g.
+ * "now", "5m", "3h", "2d", "5w". Falls back to a short localized date for
+ * anything older than ~8 weeks. A non-finite timestamp yields an empty string
+ * so the UI can render nothing rather than "Invalid Date".
  *
- * `now` is injectable for deterministic tests.
+ * `now` is injectable for deterministic tests. This is the number-based core
+ * shared by commit rows (ISO via `formatRelativeTime`) and chat-history rows
+ * (epoch-ms `lastActivityAt`).
  */
-export function formatRelativeTime(iso: string, now: number = Date.now()): string {
-  const then = Date.parse(iso)
-  if (Number.isNaN(then)) return ''
+export function formatRelativeTimeFromMs(ms: number, now: number = Date.now()): string {
+  if (!Number.isFinite(ms)) return ''
 
-  const diffMs = now - then
+  const diffMs = now - ms
   // Future timestamps (clock skew) clamp to "now" rather than negative values.
   const seconds = Math.max(0, Math.floor(diffMs / 1000))
 
@@ -24,9 +25,20 @@ export function formatRelativeTime(iso: string, now: number = Date.now()): strin
   const weeks = Math.floor(days / 7)
   if (weeks < 8) return `${weeks}w`
 
-  return new Date(then).toLocaleDateString(undefined, {
+  return new Date(ms).toLocaleDateString(undefined, {
     year: 'numeric',
     month: 'short',
     day: 'numeric'
   })
 }
+
+/**
+ * Format an ISO 8601 timestamp as a compact relative time for commit rows.
+ * Delegates to `formatRelativeTimeFromMs` after parsing; invalid input yields
+ * an empty string. `now` is injectable for deterministic tests.
+ */
+export function formatRelativeTime(iso: string, now: number = Date.now()): string {
+  const then = Date.parse(iso)
+  if (Number.isNaN(then)) return ''
+  return formatRelativeTimeFromMs(then, now)
+}