A flaky test exposed a Redis client use-after-free

# Summary A flaky test in a Redis client library exposed a use-after-free memory corruption bug at Buildkite. After tests suddenly became unreliable following a Redis upgrade, the engineering team investigated and discovered the bug was caused by data corruption that occurred before its manifestation, making it difficult to diagnose using standard debugging tools. The investigation revealed that race conditions in their test environment—involving a web server, database, and Redis server—were triggering the memory corruption issue.