Harden async task flows and enhance analysis tooling

client/src/hooks/useBackgroundTask.ts

@@ -5,6 +5,9 @@ export function useBackgroundTask(taskId: string | null | undefined) {
     { taskId: taskId || "" },
     {
       enabled: Boolean(taskId),
+      retry: 3,
+      retryDelay: (attempt) => Math.min(1_000 * 2 ** attempt, 8_000),
+      placeholderData: (previous) => previous,
       refetchInterval: (query) => {
         const task = query.state.data;
         if (!task) return 3_000;