fix(@angular/build): preserve error stack traces during prerendering

[maruthang]

PR Checklist

• The commit message follows our guidelines: https://github.com/angular/angular-cli/blob/main/CONTRIBUTING.md#-commit-message-guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

• Bugfix

What is the current behavior?

When prerendering fails, the error output shows only the error message but no stack trace, making debugging very difficult. This is because the nullish coalescing chain err.message ?? err.stack ?? err always resolves to err.message (since it's almost always defined on Error objects), so err.stack is never reached.

Issue Number: #32503

What is the new behavior?

Reorder the chain to err.stack ?? err.message ?? err at all three error-handling locations in prerender.ts. Since err.stack includes the message as its first line plus the full trace, this preserves all debugging information.

Does this PR introduce a breaking change?

• Yes
• No

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[gemini-code-assist]

Code Review

This pull request reorders error property access to prioritize stack traces over messages when reporting failures during the prerendering process. The reviewer suggested enhancing type safety and consistency across the file by utilizing assertIsError within the catch blocks and ensuring the error code is included in all error messages.

[gemini-code-assist]

For consistency with other error handling in this file (see line 370) and to improve type safety, it is a good practice to assert the error type using assertIsError. This also allows you to safely include err.code in the error message, which can be valuable for debugging, especially for potential filesystem errors from readFile in getAllRoutes.

    assertIsError(err);
    return {
      errors: ["An error occurred while extracting routes.\n\n" + (err.stack ?? err.message ?? err.code ?? err)],
      serializedRouteTree: [],
      appShellRoute: undefined,
    };

[gemini-code-assist]

To ensure type safety and for consistency with other error handling in this file (e.g., line 370), consider adding assertIsError(err) at the beginning of this catch block. This will guarantee that err is an Error object before its properties are accessed.

          assertIsError(err);
          errors.push(
            "An error occurred while prerendering route '" + route + "'.\n\n" + (err.stack ?? err.message ?? err.code ?? err),
          );
          void renderWorker.destroy();