Mark selected thread as visited in web store

apps/web/src/routes/__root.tsx

@@ -67,6 +67,15 @@ function EventRouter() {
     });
   }, [activeThreadId, api, dispatch, queryClient]);
 
+  useEffect(() => {
+    if (!activeThreadId) return;
+    dispatch({
+      type: "MARK_THREAD_VISITED",
+      threadId: activeThreadId,
+      visitedAt: new Date().toISOString(),
+    });
+  }, [activeThreadId, dispatch]);
+
   useEffect(() => {
     if (!api) return;
     return api.terminal.onEvent((event) => {

apps/web/src/store.test.ts

@@ -815,6 +815,24 @@ describe("store reducer thread continuity", () => {
     expect(next.threads[0]?.lastVisitedAt).toBe(completedAt);
   });
 
+  it("marks a thread as visited when selected", () => {
+    const state = makeState(
+      makeThread({
+        latestTurnCompletedAt: "2026-02-08T10:00:10.000Z",
+        lastVisitedAt: "2026-02-08T10:00:00.000Z",
+      }),
+    );
+
+    const nextVisitedAt = "2026-02-08T10:00:20.000Z";
+    const next = reducer(state, {
+      type: "MARK_THREAD_VISITED",
+      threadId: "thread-local-1",
+      visitedAt: nextVisitedAt,
+    });
+
+    expect(next.threads[0]?.lastVisitedAt).toBe(nextVisitedAt);
+  });
+
   it("reverts thread state to a checkpoint snapshot", () => {
     const state = makeState(
       makeThread({

apps/web/src/store.ts

@@ -105,6 +105,7 @@ type Action =
       branch: string | null;
       worktreePath: string | null;
     }
+  | { type: "MARK_THREAD_VISITED"; threadId: string; visitedAt?: string }
   | { type: "SET_RUNTIME_MODE"; mode: RuntimeMode }
   | { type: "DELETE_THREAD"; threadId: string };
 
@@ -1141,6 +1142,17 @@ export function reducer(state: AppState, action: Action): AppState {
       };
     }
 
+    case "MARK_THREAD_VISITED": {
+      const visitedAt = action.visitedAt ?? new Date().toISOString();
+      return {
+        ...state,
+        threads: updateThread(state.threads, action.threadId, (t) => ({
+          ...t,
+          lastVisitedAt: visitedAt,
+        })),
+      };
+    }
+
     case "SET_RUNTIME_MODE":
       return {
         ...state,