feat(tanstackstart-react): Auto-instrument server function middleware

[nicohrubec]

Depends on: #18989 (i.e. no need to review until that is merged)

Follow up to #18844

Extending auto-instrumentation to non-global server function middleware.

TSS function middleware docs

Closes #18847

[cursor]

Switch statement skips server function middleware in start files

Medium Severity

The switch (true) statement treats file types as mutually exclusive. If a file is both a "start file" (isStartFile) AND contains createServerFn().middleware([...]) (isServerFnFile), the case isStartFile: branch matches first and breaks, preventing the server function middleware from being wrapped. The server function middleware in such files would silently fail to be auto-instrumented.

 

[cursor]

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

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[cursor]

Route regex matches destructuring patterns causing invalid output

Low Severity

The wrapRouteMiddleware regex /(middleware)\s*:\s*\[([^\]]*)\]/g matches any middleware: [...] pattern, including JavaScript destructuring assignments. If a route file contains destructuring like const { middleware: [first] } = config;, it gets transformed to const { middleware: wrapMiddlewaresWithSentry({ first }) } = config; which is syntactically invalid JavaScript (function calls cannot appear on the left side of destructuring). This would cause a build failure.