M15: synchronize contracts and acceptance

frontend/src/context/AuthContext.tsx

@@ -1,5 +1,5 @@
 import { createContext, useCallback, useContext, useEffect, useState, type ReactNode } from "react";
-import { api, onUnauthorized } from "../api/client";
+import { api, ApiError, onUnauthorized } from "../api/client";
 import type { CurrentUser, Role, SystemStatus } from "../api/types";
 
 interface AuthState {
@@ -93,13 +93,28 @@ export function AuthProvider({ children }: { children: ReactNode }) {
   }, []);
 
   const logout = useCallback(async () => {
-    setUser(null);
-    cacheUser(null);
     try {
-      await api.post("/api/v1/auth/logout");
+      // A logout response expires an HttpOnly cookie. Chromium can expose a very small
+      // race between resolving fetch() and applying that Set-Cookie header to an
+      // immediate top-level navigation. Confirm the server now rejects the session
+      // before allowing the router to continue; retrying logout is idempotent.
+      for (let attempt = 0; attempt < 3; attempt += 1) {
+        await api.post("/api/v1/auth/logout");
+        try {
+          await api.get<CurrentUser>("/api/v1/auth/session");
+        } catch (err) {
+          if (err instanceof ApiError && err.status === 401) return;
+          throw err;
+        }
+      }
     } catch {
       // Best effort: the cookie is cleared server-side when it works, and the client has
-      // already dropped its own state either way.
+      // still drops its own state when the request itself is unavailable.
+    } finally {
+      // Keep RequireAuth from redirecting to /login while the server-side invalidation
+      // is still in flight. Otherwise a very fast navigation can race ahead of logout.
+      setUser(null);
+      cacheUser(null);
     }
   }, []);