Release v21.12.1

Summary

A one-shot HTTP read of a collection-backed observable query with waitForFirstResult=true returned the observable's empty seed value with isReady: true, deterministically and regardless of the timeout. Because the payload was a well-formed empty collection and the result reported itself as ready, a caller had no way to tell it apart from a genuinely empty read model. Anything that cannot hold a stream open was affected: cURL and scripted reads, readiness probes, integration specs, and server-to-server fetches.

Fixed

• waitForFirstResult=true on a MongoDB collection-backed observable query now resolves on the initial query result instead of the empty seed emission that preceded it (#2535)
• A subscriber that connects to a MongoDB observable query after its initial query completed now receives that result, rather than waiting for the next change