fix(rate-limiter): incorrectly applying to non-configured fields

[Tolsee]

Description

Fixed a bug where the rate limiter plugin was incorrectly applying rate limiting to GraphQL fields not configured in configByField. Fields that should be unlimited were getting rate limited with default error messages.

The root cause was that { ...(rateLimitDirective ?? fieldConfig) } creates an empty object {} when both values are undefined, which is truthy, causing rate limiting to be applied to all fields.

Fixes #2689

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Screenshots/Sandbox (if appropriate/relevant):

N/A - This is a backend logic fix with test coverage.

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• Added regression test 'should not rate limit fields that are not in configByField'
• Verified all existing rate limiter tests continue to pass
• Tested that configured fields are properly rate limited
• Tested that unconfigured fields are never rate limited

Test Environment:

• OS: macOS
• @envelop/rate-limiter: 8.1.0
• NodeJS: 24.7.0

Checklist:

• I have followed the CONTRIBUTING doc and the style guidelines of this project
• I have performed a self-review of my own code
• I have commented on my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[EmrysMyrddin]

Great catch! Thank you very much for the fix!

I took the freedom to push a changeset to your branch so that I can release as quickly as possible.