[feywind]

Stack Structure (Stack #36644)

Layer	Branch	PR
1	hedging/options-and-token-bucket	#36639
2	hedging/coordinator-and-scheduler	#36640
3	hedging/queue-integration	#36641
4	hedging/queue-unit-tests	#36642 (this PR)
5	hedging/system-tests	#36643

Summary

Implements Layer 4 of Cloud Pub/Sub Publish Hedging (go/sdk:pubsub-hedging) for google-cloud-pubsub:

• AsyncPublisher hedging unit tests (test/google/cloud/pubsub/async_publisher_hedging_test.rb):
  • Default and custom hedging configuration, enabled: false, bounds/timeout validation on AsyncPublisher.new and pubsub.publisher, mutual exclusion with enable_message_ordering!, and ordered batch bypass.
  • Cold-start empty token bucket (0.0), warmup to 1.0 token, hedge consumption, and rate-limited logging on pubsub:publish-hedged.
  • Race outcomes: hedged attempt 1 wins and cancels attempt 0; attempt 0 wins before hedge_delay; attempt 0 wins after hedge dispatch and cancels attempt 1; multiple hedging (attempt 2 wins and cancels attempt 0 and attempt 1).
  • Asymmetric error handling when a hedged attempt fails vs. when attempt 0 fails terminally.
• Service#publish & TopicAdmin::Client cancellation unit tests (test/google/cloud/pubsub/service_test.rb):
  • Verifies CancellableRetryPolicy construction, mid-flight gRPC Operation#cancel without retrying GRPC::Cancelled, and immediate interruption of retry backoff sleep.