diff --git a/packages/client-runtime/src/state/threadVisits.test.ts b/packages/client-runtime/src/state/threadVisits.test.ts
index adcac7139e82a..c67ca4fa807c9 100644
--- a/packages/client-runtime/src/state/threadVisits.test.ts
+++ b/packages/client-runtime/src/state/threadVisits.test.ts
@@ -111,6 +111,25 @@ it("keeps a mark-unread on the open thread until new activity lands", () => {
   expect(t.visits.slice(1)).toEqual([{ threadId: t.ref.threadId, visitedAt: at(30) }]);
 });
 
+it("keeps a mark-unread on a read thread reopened within the open dedupe window", () => {
+  using t = setup("thread-unread-reopened", {
+    updatedAt: at(10),
+    lastVisitedAt: at(10),
+    latestRun: { completedAt: at(9) },
+  });
+  claimThreadOpen(environmentId, t.ref.threadId, Date.UTC(2026, 0, 1));
+  t.mount();
+  t.update({ lastVisitedAt: at(8) });
+  vi.advanceTimersByTime(VISIT_DISPATCH_THROTTLE_MS);
+  expect(t.visits).toEqual([]);
+
+  // An authoritative snapshot can briefly replace the row with an older one.
+  t.update({ updatedAt: at(5), lastVisitedAt: at(5), latestRun: { completedAt: at(4) } });
+  t.update({ updatedAt: at(10), lastVisitedAt: at(8), latestRun: { completedAt: at(9) } });
+  vi.advanceTimersByTime(VISIT_DISPATCH_THROTTLE_MS);
+  expect(t.visits).toEqual([]);
+});
+
 it("keeps mark unread sticky after an expired wake is retired", () => {
   using t = setup("thread-unread-retired-wake", {
     updatedAt: at(10),
diff --git a/packages/client-runtime/src/state/threadVisits.ts b/packages/client-runtime/src/state/threadVisits.ts
index c08f47ed01436..e63c2ad9c0279 100644
--- a/packages/client-runtime/src/state/threadVisits.ts
+++ b/packages/client-runtime/src/state/threadVisits.ts
@@ -114,7 +114,12 @@ export function createThreadVisitTracker(options: ThreadVisitTrackerOptions) {
           return;
         }
         const lastVisitedAtMs = shell.lastVisitedAt ? Date.parse(shell.lastVisitedAt) : NaN;
-        if (!Number.isNaN(lastVisitedAtMs) && lastVisitedAtMs >= updatedAtMs) return;
+        if (!Number.isNaN(lastVisitedAtMs) && lastVisitedAtMs >= updatedAtMs) {
+          // Already seen, so a later mark-unread stays sticky even when no open was sent.
+          if (lastDispatchedUpdatedAt === null || Date.parse(lastDispatchedUpdatedAt) < updatedAtMs)
+            lastDispatchedUpdatedAt = visitedAt;
+          return;
+        }
         if (lastDispatchedUpdatedAt !== null && Date.parse(lastDispatchedUpdatedAt) >= updatedAtMs)
           return;