Add integration tests and improvements for creator endpoints

[Georgechisom]

Summary

This PR addresses four issues related to creator endpoints by adding integration tests and utility improvements to enhance stability, maintainability, and observability.

Changes

Integration Test for Sort Stability (Issue #366)

Added integration test to verify that creator list responses maintain stable ordering when multiple creators share identical sort field values. The test confirms that a tie-breaker field (id) is consistently applied to prevent undefined ordering across repeated requests.

Files:

• src/modules/creators/creator-list-sort-stability.integration.test.ts

Safe Nested Field Reader Helper (Issue #365)

Implemented a utility helper for safely reading nested optional fields from creator response objects. This reduces boilerplate null checks and prevents null reference errors throughout the codebase.

Files:

• src/utils/safe-nested-read.utils.ts
• src/utils/safe-nested-read.utils.test.ts
• src/modules/creators/creator-list-item.mapper.ts (applied helper)
• src/modules/creators/creators.serializers.ts (applied helper)

Structured Cache Eviction Logs (Issue #367)

Added debug-level structured logging for cache eviction events on creator endpoints. Logs include cache key and eviction reason (expired, stale, or overflow) to help operators understand cache churn and tune TTLs.

Files:

• src/modules/creators/creators.cache.ts

Content-Type Header Integration Test (Issue #344)

Added integration tests to verify that creator route responses always include the correct Content-Type header. This prevents regressions when middleware or serialization changes are made.

Files:

• src/modules/creators/creator-route-content-type.integration.test.ts
• src/utils/api-response.utils.ts (ensured Content-Type is set)

Testing

All new tests pass successfully:

• 3 test suites added
• 30 tests passing
• No test failures

Ran test command:

pnpm exec jest --testPathPatterns="creator-list-sort-stability|safe-nested-read|creator-route-content-type" --no-coverage

Acceptance Criteria

All acceptance criteria from the issues have been met:

• Sort order is identical across repeated requests for creators with duplicate sort values
• Helper returns field value when present, default when null or absent
• Cache eviction emits debug-level log with key and reason
• Content-Type header is present on all tested creator route responses

Closes #366
Closes #365
Closes #367
Closes #344

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