fix(react-router): Respect custom default integrations (#25259)

The React Router Node SDK overwrites `defaultIntegrations`, so `false`,
`[]`, and custom arrays are ignored. Only generate the framework
defaults when the option is unset, matching the underlying Node SDK's
behavior.

Co-authored-by: Codex <codex@openai.com>

Author: nicohrubec

packages/react-router/src/server/sdk.ts

@@ -24,7 +24,7 @@ export function getDefaultReactRouterServerIntegrations(options: NodeOptions): I
 export function init(options: NodeOptions): NodeClient | undefined {
   const opts: NodeOptions = {
     ...options,
-    defaultIntegrations: getDefaultReactRouterServerIntegrations(options),
+    defaultIntegrations: options.defaultIntegrations ?? getDefaultReactRouterServerIntegrations(options),
   };
 
   DEBUG_BUILD && debug.log('Initializing SDK...');

packages/react-router/test/server/sdk.test.ts

@@ -46,6 +46,26 @@ describe('React Router server SDK', () => {
       expect(client).not.toBeUndefined();
     });
 
+    it.each([
+      { value: 'false', defaultIntegrations: false as const },
+      { value: 'an empty array', defaultIntegrations: [] },
+    ])('disables default integrations when set to $value', ({ defaultIntegrations }) => {
+      const client = reactRouterInit({ defaultIntegrations });
+
+      expect(client?.getOptions().integrations.map(integration => integration.name)).toEqual(['SpanStreaming']);
+    });
+
+    it('replaces default integrations with a custom array', () => {
+      const integration = { name: 'CustomIntegration' };
+
+      const client = reactRouterInit({ defaultIntegrations: [integration] });
+
+      expect(client?.getOptions().integrations.map(integration => integration.name)).toEqual([
+        'CustomIntegration',
+        'SpanStreaming',
+      ]);
+    });
+
     it('adds the low quality transactions filter integration by default', () => {
       const filterSpy = vi.spyOn(LowQualityModule, 'lowQualityTransactionsFilterIntegration');