fix(review): compare a reply's update time to the whole second in head checks (#1081)

A stored reply time can hold whole seconds where the newest-page list returns
fractions of a second. The head check compared them to the millisecond, so
such a reply read as changed on every look and the signal never cleared. Both
sides are now compared at whole-second precision. A reply whose update time
moved by a second or more still signals.

Co-authored-by: Claude Sonnet 5.5 <noreply@anthropic.com>

Author: kodes-agency

src/contexts/review/domain/head-check.test.ts

@@ -167,6 +167,35 @@ describe('compareHead: what a head page would persist', () => {
       expect(result.replyChangedCount).toBe(0)
     })
 
+    it.each([
+      ['2026-10-20T12:00:00.000Z', '2026-10-20T12:00:00.789Z'],
+      ['2026-10-20T12:00:00.999Z', '2026-10-20T12:00:00.001Z'],
+    ])('ignores reply fractions on both sides (%s, %s)', (storedTime, listTime) => {
+      const result = compare({
+        reviews: [google({ replyText: 'Thanks', replyUpdatedAt: new Date(listTime) })],
+        copies: [
+          stored({ reply: { state: 'live', providerUpdatedAt: new Date(storedTime) } }),
+        ],
+      })
+
+      expect(result).toMatchObject({ replyChangedCount: 0, wouldPersist: 0 })
+    })
+
+    it.each([1000, 2000])('signals a real reply change %s ms apart', (difference) => {
+      const storedTime = new Date('2026-10-20T12:00:00.789Z')
+      const result = compare({
+        reviews: [
+          google({
+            replyText: 'Thanks',
+            replyUpdatedAt: new Date(storedTime.getTime() + difference),
+          }),
+        ],
+        copies: [stored({ reply: { state: 'live', providerUpdatedAt: storedTime } })],
+      })
+
+      expect(result).toMatchObject({ replyChangedCount: 1, wouldPersist: 1 })
+    })
+
     it('does not count no reply on both sides', () => {
       const result = compare({
         reviews: [google()],

src/contexts/review/domain/head-check.ts

@@ -90,8 +90,13 @@ export type HeadComparison = Readonly<{
   hasMore: boolean
 }>
 
-const sameInstant = (a: Date | null, b: Date | null): boolean =>
-  (a === null && b === null) || (a !== null && b !== null && a.getTime() === b.getTime())
+// A stored reply time can hold whole seconds where the newest-page list returns
+// fractions of a second, so the two are compared to the second.
+const sameSecond = (a: Date | null, b: Date | null): boolean =>
+  (a === null && b === null) ||
+  (a !== null &&
+    b !== null &&
+    Math.floor(a.getTime() / 1000) === Math.floor(b.getTime() / 1000))
 
 /** Google's updateTime is newer than the stored one (or there is none stored). */
 const updatedSince = (google: HeadGoogleReview, copy: HeadStoredCopy): boolean => {
@@ -123,7 +128,7 @@ const isReplyChanged = (google: HeadGoogleReview, copy: HeadStoredCopy): boolean
   const storedHasReply = copy.reply?.state === 'live'
   if (googleHasReply !== storedHasReply) return true
   if (!googleHasReply) return false
-  return !sameInstant(google.replyUpdatedAt, copy.reply?.providerUpdatedAt ?? null)
+  return !sameSecond(google.replyUpdatedAt, copy.reply?.providerUpdatedAt ?? null)
 }
 
 const needsLeaseRefresh = (copy: HeadStoredCopy, now: Date): boolean =>