[codex] Fix visited timestamp under clock skew

apps/web/src/components/ChatView.tsx

@@ -1021,7 +1021,10 @@
     const lastVisitedAt = activeThreadLastVisitedAt ? Date.parse(activeThreadLastVisitedAt) : NaN;
     if (!Number.isNaN(lastVisitedAt) && lastVisitedAt >= turnCompletedAt) return;
 
-    markThreadVisited(scopedThreadKey(scopeThreadRef(serverThread.environmentId, serverThread.id)));
+    markThreadVisited(
+      scopedThreadKey(scopeThreadRef(serverThread.environmentId, serverThread.id)),
+      activeLatestTurn.completedAt,
+    );
   }, [
     activeLatestTurn?.completedAt,
     activeThreadLastVisitedAt,
@@ -1576,7 +1579,7 @@
   );
 
   const focusComposer = useCallback(() => {
     composerRef.current?.focusAtEnd();
   }, []);
   const scheduleComposerFocus = useCallback(() => {
     window.requestAnimationFrame(() => {
@@ -1584,7 +1587,7 @@
     });
   }, [focusComposer]);
   const addTerminalContextToDraft = useCallback((selection: TerminalContextSelection) => {
     composerRef.current?.addTerminalContext(selection);
   }, []);
   const setTerminalOpen = useCallback(
     (open: boolean) => {
@@ -2263,7 +2266,7 @@
       const shortcutContext = {
         terminalFocus: isTerminalFocused(),
         terminalOpen: Boolean(terminalState.terminalOpen),
         modelPickerOpen: composerRef.current?.isModelPickerOpen() ?? false,
       };
 
       const command = resolveShortcutCommand(event, keybindings, {
@@ -2798,7 +2801,7 @@
         };
       });
       promptRef.current = "";
       composerRef.current?.resetCursorState({ cursor: 0 });
     },
     [activePendingProgress?.activeQuestion, activePendingUserInput],
   );
@@ -2825,7 +2828,7 @@
           ),
         },
       }));
       const snapshot = composerRef.current?.readSnapshot();
       if (
         snapshot?.value !== value ||
         snapshot.cursor !== nextCursor ||
@@ -2888,7 +2891,7 @@
         return;
       }
 
       const sendCtx = composerRef.current?.getSendContext();
       if (!sendCtx) {
         return;
       }
@@ -3024,7 +3027,7 @@
       return;
     }
 
     const sendCtx = composerRef.current?.getSendContext();
     if (!sendCtx) {
       return;
     }

apps/web/src/uiStateStore.test.ts

@@ -4,6 +4,7 @@
 import {
   clearThreadUi,
   hydratePersistedProjectState,
+  markThreadVisited,
   markThreadUnread,
   PERSISTED_STATE_KEY,
   type PersistedUiState,
@@ -27,6 +28,28 @@
 }
 
 describe("uiStateStore pure functions", () => {
+  it("markThreadVisited stores the provided server timestamp", () => {
+    const threadId = ThreadId.make("thread-1");
+    const initialState = makeUiState();
+
+    const next = markThreadVisited(initialState, threadId, "2026-02-25T12:30:00.700Z");
+
+    expect(next.threadLastVisitedAtById[threadId]).toBe("2026-02-25T12:30:00.700Z");
+  });
+
+  it("markThreadVisited does not move visit state backwards under clock skew", () => {
+    const threadId = ThreadId.make("thread-1");
+    const initialState = makeUiState({
+      threadLastVisitedAtById: {
+        [threadId]: "2026-02-25T12:30:00.700Z",
+      },
+    });
+
+    const next = markThreadVisited(initialState, threadId, "2026-02-25T12:30:00.000Z");
+
+    expect(next).toBe(initialState);
+  });
+
   it("markThreadUnread moves lastVisitedAt before completion for a completed thread", () => {
     const threadId = ThreadId.make("thread-1");
     const latestTurnCompletedAt = "2026-02-25T12:30:00.000Z";
@@ -409,7 +432,7 @@
 });
 
 describe("uiStateStore persistence round-trip", () => {
   function createLocalStorageStub(): Storage {
     const store = new Map<string, string>();
     return {
       clear: () => {