feat(sidebar): show compact timestamp in recent activity rows

The sidebar's recent activity list (SidebarActivitySections) rendered its
session rows without an inline timestamp on web/desktop — the compact
relative label only appeared in the hover tooltip and on touch runtimes.

Render the existing i18n-backed formatSessionCompactDateLabel inline in
the recent rows' metadata slot, alongside the goal/branch glyphs, for
web/desktop too. It keeps the same hover-fade as the other metadata, so
the hover-revealed row actions never overlap it, and the full date
stays available in the row tooltip.

No new strings: the label reuses common.relative.* keys.

Fixes #2560

packages/ui/src/components/session/sidebar/SessionNodeItem.test.ts

@@ -0,0 +1,41 @@
+import { describe, expect, test } from 'bun:test';
+import { readFileSync } from 'node:fs';
+
+const source = readFileSync(new URL('./SessionNodeItem.tsx', import.meta.url), 'utf8');
+
+describe('SessionNodeItem recent-activity timestamp', () => {
+  test('the recent activity rows render the compact timestamp in the inline metadata slot', () => {
+    // The right-slot guard must open for recent rows even when no activity,
+    // goal glyph, or branch marker is present.
+    const guard = source.indexOf("showActivityDuration || sessionGoalGlyph || showInlineBranchMarker || renderContext === 'recent'");
+    expect(guard).toBeGreaterThan(-1);
+    // The recent-only block sits inside that slot…
+    const guardOpen = source.indexOf("{renderContext === 'recent' ? (", guard);
+    expect(guardOpen).toBeGreaterThan(guard);
+    // …and the compact label rendered there is the first one after it.
+    const label = source.indexOf('{sessionCompactUpdatedLabel}', guardOpen);
+    expect(label).toBeGreaterThan(guardOpen);
+    // The only later occurrence is the pre-existing row tooltip (which shows
+    // the full date), not a second inline render.
+    const tooltipLabel = source.indexOf('{sessionCompactUpdatedLabel}', label + 1);
+    expect(tooltipLabel).toBeGreaterThan(label);
+    expect(source.indexOf('title={sessionUpdatedLabel}', tooltipLabel - 80)).toBeGreaterThan(-1);
+  });
+
+  test('the timestamp shares the hover-fade of the other metadata so revealed actions never overlap it', () => {
+    const guard = source.indexOf("showActivityDuration || sessionGoalGlyph || showInlineBranchMarker || renderContext === 'recent'");
+    // The slot content fades out while the row is hovered (hideOnHoverClass)
+    // and while the row menu is open — the same span that now carries the
+    // recent timestamp.
+    const hideOnHover = source.indexOf('hideOnHoverClass', guard);
+    expect(hideOnHover).toBeGreaterThan(guard);
+    expect(hideOnHover).toBeLessThan(source.indexOf("{renderContext === 'recent' ? (", guard));
+  });
+
+  test('the compact label uses the existing i18n-backed relative time helper', () => {
+    // formatSessionCompactDateLabel (already used by touch runtimes and the
+    // row tooltip) is the source of the label — no new formatting code.
+    expect(source.indexOf('const sessionCompactUpdatedLabel = formatSessionCompactDateLabel(sessionTimestamp);')).toBeGreaterThan(-1);
+    expect(source.indexOf('{sessionCompactUpdatedLabel}')).toBeGreaterThan(-1);
+  });
+});

packages/ui/src/components/session/sidebar/SessionNodeItem.tsx

@@ -1257,7 +1257,7 @@ function SessionNodeItemComponent(props: Props): React.ReactNode {
                             </>
                           )}
                         </span>
-                      ) : (showActivityDuration || sessionGoalGlyph || showInlineBranchMarker) ? (
+                      ) : (showActivityDuration || sessionGoalGlyph || showInlineBranchMarker || renderContext === 'recent') ? (
                         <div className="relative ml-1 flex h-4 flex-shrink-0 items-center justify-end">
                           <span className={cn(
                             'inline-flex items-center gap-1 whitespace-nowrap text-right transition-opacity duration-150',
@@ -1281,6 +1281,18 @@ function SessionNodeItemComponent(props: Props): React.ReactNode {
                                     style={prIconColor ? { color: prIconColor } : undefined}
                                   />
                                 ) : null}
+                                {/* The recent activity list shows its compact
+                                    timestamp inline (touch runtimes already get
+                                    it through the alwaysShowActions branch);
+                                    it shares the slot with the goal/branch
+                                    metadata and hides on hover exactly like
+                                    them, so the revealed row actions never
+                                    overlap it. */}
+                                {renderContext === 'recent' ? (
+                                  <span className="flex-shrink-0 text-[0.72rem] leading-none text-muted-foreground/75 tabular-nums">
+                                    {sessionCompactUpdatedLabel}
+                                  </span>
+                                ) : null}
                               </>
                             )}
                           </span>