Make app data loading safe under StrictMode

e2e/fixtures/app-data-probe.js

@@ -0,0 +1,44 @@
+// Rôle : observe le chargement réel de l'application avec des réponses réseau contrôlées sous StrictMode.
+import { createElement, StrictMode, useLayoutEffect } from "react";
+import { createRoot } from "react-dom/client";
+import { flushSync } from "react-dom";
+import { useAppData } from "../../website/src/hooks/useAppData.js";
+
+export function mountAppDataProbe(element, initialRoute) {
+  const originalFetch = globalThis.fetch;
+  const requests = [];
+  const snapshots = [];
+  const root = createRoot(element);
+  globalThis.fetch = (url, { signal } = {}) => new Promise((resolve) => {
+    // Le double ignore volontairement abort pour tester aussi les réponses déjà en cours.
+    requests.push({ url, signal, resolve, settled: false });
+  });
+
+  function Probe({ route }) {
+    const data = useAppData(route);
+    useLayoutEffect(() => { snapshots.push(data); });
+    return createElement("pre", { id: "data-state" }, JSON.stringify(data));
+  }
+
+  function navigate(route) {
+    snapshots.length = 0;
+    flushSync(() => root.render(createElement(StrictMode, null, createElement(Probe, { route }))));
+  }
+  navigate(initialRoute);
+  return {
+    snapshots,
+    requests: () => requests.map(({ url, signal, settled }) => ({ url, aborted: signal?.aborted, settled })),
+    respond(url, payload, status = 200, aborted = false) {
+      for (const request of requests) {
+        if (request.url !== url || request.settled || request.signal?.aborted !== aborted) continue;
+        request.settled = true;
+        request.resolve({ ok: status >= 200 && status < 300, json: async () => payload });
+      }
+    },
+    navigate,
+    unmount() {
+      flushSync(() => root.unmount());
+      globalThis.fetch = originalFetch;
+    }
+  };
+}