feat(tanstackstart-react): Auto-instrument global middleware

[nicohrubec]

Depends on (i.e. do not review until the following is merged): vite plugin PR

This PR adds automatic instrumentation for global request and function middleware in TanStack Start applications.

Overview

The sentryTanstackStart Vite plugin now automatically wraps requestMiddleware and functionMiddleware arrays in createStart() with Sentry instrumentation. This is done via a source code transformation during the build that converts:

createStart({
  requestMiddleware: [myMiddleware],
  functionMiddleware: [anotherMiddleware],
});

into:

import { wrapMiddlewaresWithSentry } from '@sentry/tanstackstart-react';

createStart({
  requestMiddleware: wrapMiddlewaresWithSentry({ myMiddleware }),
  functionMiddleware: wrapMiddlewaresWithSentry({ anotherMiddleware }),
});

Usage

Auto-instrumentation is enabled by default. To explicitly disable it:

// vite.config.ts
import { sentryTanstackStart } from '@sentry/tanstackstart-react';

export default defineConfig({
  plugins: [
    sentryTanstackStart({
      org: 'your-org',
      project: 'your-project',
      autoInstrumentMiddleware: false, // Disable auto-instrumentation
    }),
  ],
});

This should give users flexibility in case things go wrong.

Implementation Details

• Uses a regex-based approach to transform source files containing createStart()
• Skips transformation if the user has already manually wrapped middlewares with wrapMiddlewaresWithSentry
• Only handles simple identifier arrays (e.g., [foo, bar]), not complex expressions

Testing

• Updated E2E tests to use auto-instrumentation for global middleware
• Updated unit tests for the sentryTanstackStart plugin
• Added unit tests for autoInstrumentMiddleware

Follow-ups

Future PRs will add support for non-global request/function middleware. This PR focuses on global middleware to make it a bit easier to review. I also want to give users a bit more control by allowing them to disable auto-instrumentation on a file-level, but this doesn't make sense yet since the current implementation only patches a single file anyways.

Closes #18845

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Cursor Bugbot has reviewed your changes and found 1 potential issue.

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Regex transformation modifies strings and comments containing pattern

Low Severity

The regex /(requestMiddleware|functionMiddleware)\s*:\s*\[([^\]]*)\]/g matches patterns anywhere in the source file without respecting JavaScript syntax boundaries. This means string literals or comments containing patterns like requestMiddleware: [foo] would also be transformed. For example, a comment documenting config format or a string used for code generation could be unintentionally modified to include wrapMiddlewaresWithSentry({ foo }), causing misleading documentation or broken string content.