[sideeffffect]

fs2-kafka 4.1.0 is out on Maven Central, and it ships the two pieces that 0.15.0-RC1 was waiting on from typelevel/fs2-kafka#1522: mapK on the committable consumer types and imapK on KafkaProducer. With those available, the four areas that had to be temporarily disabled during the fs2-kafka 4.x migration can come back, which unblocks the final 0.15.0.

What this restores

• TracedConsumer.injectK — lifts the traced stream into G and rebuilds each record with CommittableConsumerRecord#mapK, which replaces the old package-private CommittableOffset reconstruction.
• TracedProducer.create — wraps the producer in G via KafkaProducer#imapK, including the transactional methods that 4.x folded into KafkaProducer.
• the injectK / traceK stream syntax and the liftTrace producer syntax in Fs2KafkaSyntax, plus their imports.

Dependency bump

fs2-kafka goes from 4.0.0 to 4.1.0 in project/dependencies.conf. That is the release that makes mapK / imapK available.

Signature note

TracedProducer.create keeps the intended shape from the sketch, with one small change: the Monad[G] context bound is dropped because the implicit MonadCancelThrow[G] already implies Monad[G], and leaving it in trips -Werror as an unused implicit. Everything else matches the commented-out signatures that were left in main.

The consumer.group span attribute stays dropped — CommittableOffset.consumerGroupId is genuinely gone in fs2-kafka 4.x, so there is nothing to restore there.

Checks

sbt ci-test is green locally: scalafmt / scalafix, versionPolicyCheck, mdoc, publishLocal, and +test all pass, cross-built on Scala 2.13.18 and 3.3.8.