fix(widgets): prevent stale cache from serving errored data

Add two layers on top of PR #6399's error boundary recovery:

Layer 1 — QueryCache subscriber (query-cache-error-cleanup.ts):
Subscribe to QueryCache events. When a persistable query transitions
from success to error, resetQueries clears stale data so widgets show
error/loading UI instead of rendering incompatible cached values.
Uses resetQueries (not removeQueries) so active observers get a
refetch triggered rather than being orphaned with a destroyed query.

Layer 2 — Rehydration invalidation (trpc.tsx):
Add onSuccess callback to PersistQueryClientProvider that invalidates
all persistable queries after rehydration. Combined with staleTime: 0,
this ensures rehydrated persisted data is immediately marked stale and
refetches on mount rather than being served as fresh.

Closes #6398

apps/nextjs/src/app/[locale]/_client-providers/query-cache-error-cleanup.ts

@@ -0,0 +1,29 @@
+import type { QueryClient } from "@tanstack/react-query";
+
+import { isPersistableWidgetQueryKey } from "@homarr/api/query-cache";
+
+export const createQueryCacheErrorCleanup = (queryClient: QueryClient): (() => void) => {
+  const wasSuccessful = new Set<string>();
+
+  return queryClient.getQueryCache().subscribe((event) => {
+    const query = event.query;
+    const key = query.queryHash;
+
+    if (event.type === "removed") {
+      wasSuccessful.delete(key);
+      return;
+    }
+
+    if (event.type !== "updated") return;
+
+    if (query.state.status === "success" && isPersistableWidgetQueryKey(query.queryKey)) {
+      wasSuccessful.add(key);
+      return;
+    }
+
+    if (query.state.status === "error" && wasSuccessful.has(key)) {
+      queryClient.resetQueries({ queryKey: query.queryKey, exact: true });
+      wasSuccessful.delete(key);
+    }
+  });
+};

apps/nextjs/src/app/[locale]/_client-providers/trpc.tsx

@@ -1,7 +1,7 @@
 "use client";
 
 import type { PropsWithChildren } from "react";
-import { useState } from "react";
+import { useEffect, useState } from "react";
 import type { QueryKey } from "@tanstack/react-query";
 import { QueryClient } from "@tanstack/react-query";
 import { ReactQueryDevtools } from "@tanstack/react-query-devtools";
@@ -36,6 +36,7 @@ import { env } from "@homarr/common/env";
 import { showWarningNotification } from "@homarr/notifications";
 import { widgetImports } from "@homarr/widgets";
 
+import { createQueryCacheErrorCleanup } from "./query-cache-error-cleanup";
 import { createWidgetQueryPersister } from "./query-cache-persister";
 
 const getWebSocketProtocol = () => {
@@ -102,6 +103,10 @@ export function TRPCReactProvider(props: PropsWithChildren) {
     return client;
   });
 
+  useEffect(() => {
+    return createQueryCacheErrorCleanup(queryClient);
+  }, [queryClient]);
+
   const [trpcClient] = useState(() => {
     return clientApi.createClient({
       links: [
@@ -162,6 +167,9 @@ export function TRPCReactProvider(props: PropsWithChildren) {
               query.state.status === "success" && isPersistableWidgetQueryKey(query.queryKey),
           },
         }}
+        onSuccess={() => {
+          queryClient.invalidateQueries({ predicate: (query) => isPersistableWidgetQueryKey(query.queryKey) });
+        }}
       >
         <ReactQueryStreamedHydration transformer={superjson}>{props.children}</ReactQueryStreamedHydration>
         <ReactQueryDevtools initialIsOpen={false} />

apps/nextjs/src/components/board/items/widget-query-recovery.spec.ts

@@ -1,6 +1,9 @@
 import { QueryClient } from "@tanstack/react-query";
 import { describe, expect, test } from "vitest";
 
+import { isPersistableWidgetQueryKey } from "@homarr/api/query-cache";
+
+import { createQueryCacheErrorCleanup } from "~/app/[locale]/_client-providers/query-cache-error-cleanup";
 import { removePersistedWidgetQueries } from "./widget-query-recovery";
 
 describe("removePersistedWidgetQueries", () => {
@@ -52,3 +55,103 @@ describe("removePersistedWidgetQueries", () => {
     expect(queryClient.getQueryData(unrelatedQueryKey)).toBe("unrelated");
   });
 });
+
+describe("query cache error cleanup", () => {
+  test("resets data when a persistable query transitions from success to error", async () => {
+    const queryClient = new QueryClient({ defaultOptions: { queries: { retry: false } } });
+    const unsubscribe = createQueryCacheErrorCleanup(queryClient);
+
+    const widgetKey = [["widget", "mediaServer", "getCurrentStreams"], { input: {} }];
+    const userKey = [["user", "me"], { input: {} }];
+
+    queryClient.setQueryData(widgetKey, { old: true });
+    queryClient.setQueryData(userKey, { user: true });
+
+    await queryClient
+      .fetchQuery({ queryKey: widgetKey, queryFn: () => Promise.reject(new Error("API down")) })
+      .catch(() => {});
+
+    expect(queryClient.getQueryData(widgetKey)).toBeUndefined();
+    expect(queryClient.getQueryData(userKey)).toEqual({ user: true });
+
+    unsubscribe();
+  });
+
+  test("preserves stale data for non-persistable query errors", async () => {
+    const queryClient = new QueryClient({ defaultOptions: { queries: { retry: false } } });
+    const unsubscribe = createQueryCacheErrorCleanup(queryClient);
+
+    const boardKey = [["board", "getBoardByName"], { input: {} }];
+
+    queryClient.setQueryData(boardKey, { boards: [] });
+
+    await queryClient
+      .fetchQuery({ queryKey: boardKey, queryFn: () => Promise.reject(new Error("API down")) })
+      .catch(() => {});
+
+    expect(queryClient.getQueryData(boardKey)).toEqual({ boards: [] });
+
+    unsubscribe();
+  });
+
+  test("handles success→error→success→error cycling without getting stuck", async () => {
+    const queryClient = new QueryClient({ defaultOptions: { queries: { retry: false } } });
+    const unsubscribe = createQueryCacheErrorCleanup(queryClient);
+
+    const widgetKey = [["widget", "mediaServer", "getCurrentStreams"], { input: {} }];
+
+    queryClient.setQueryData(widgetKey, "first-success");
+    await queryClient.fetchQuery({ queryKey: widgetKey, queryFn: () => Promise.resolve("second-success") });
+    expect(queryClient.getQueryData(widgetKey)).toBe("second-success");
+
+    await queryClient
+      .fetchQuery({ queryKey: widgetKey, queryFn: () => Promise.reject(new Error("boom")) })
+      .catch(() => {});
+    expect(queryClient.getQueryData(widgetKey)).toBeUndefined();
+
+    await queryClient.fetchQuery({ queryKey: widgetKey, queryFn: () => Promise.resolve("third-success") });
+    expect(queryClient.getQueryData(widgetKey)).toBe("third-success");
+
+    await queryClient
+      .fetchQuery({ queryKey: widgetKey, queryFn: () => Promise.reject(new Error("boom-2")) })
+      .catch(() => {});
+    expect(queryClient.getQueryData(widgetKey)).toBeUndefined();
+
+    unsubscribe();
+  });
+
+  test("unsubscribe stops processing further events", async () => {
+    const queryClient = new QueryClient({ defaultOptions: { queries: { retry: false } } });
+    const unsubscribe = createQueryCacheErrorCleanup(queryClient);
+
+    const widgetKey = [["widget", "mediaServer", "getCurrentStreams"], { input: {} }];
+    queryClient.setQueryData(widgetKey, "stale");
+
+    unsubscribe();
+
+    await queryClient
+      .fetchQuery({ queryKey: widgetKey, queryFn: () => Promise.reject(new Error("API down")) })
+      .catch(() => {});
+
+    expect(queryClient.getQueryData(widgetKey)).toBe("stale");
+  });
+});
+
+describe("rehydration marks persistable data as stale", () => {
+  test("rehydrated queries are invalidated so they refetch on mount", async () => {
+    const queryClient = new QueryClient({
+      defaultOptions: { queries: { retry: false, staleTime: 0 } },
+    });
+
+    const widgetKey = [["widget", "mediaServer", "getCurrentStreams"], { input: {} }];
+    const userKey = [["user", "me"], { input: {} }];
+
+    queryClient.setQueryData(widgetKey, { rehydrated: true });
+    queryClient.setQueryData(userKey, { rehydrated: true });
+
+    queryClient.invalidateQueries({ predicate: (query) => isPersistableWidgetQueryKey(query.queryKey) });
+
+    expect(queryClient.getQueryState(widgetKey)?.isInvalidated).toBe(true);
+    expect(queryClient.getQueryState(userKey)?.isInvalidated).toBe(false);
+  });
+});