Go's typed-nil trap silently crashed a rate limiter when Redis was absent

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A developer building Grounded LLM, an open-source document assistant platform, discovered a subtle Go bug during CI smoke tests for the v0.4 enterprise-hardening release. The rate limiter was designed to fall back to an in-memory backend when Redis was unavailable, but instead crashed with a hard panic on the first incoming request. The root cause was Go's typed-nil interface behavior: a nil *redis.Client pointer boxed into a redis.Cmdable interface evaluated as non-nil, tricking the limiter into enabling Redis mode despite no live client existing. The fix involved two defensive layers — returning a true nil interface at the source and adding an explicit typed-nil guard inside the WithRedis constructor — along with a regression test to prevent recurrence. The bug was caught in CI before reaching production and is now merged into the v0.4.0 release.

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