Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.
librdkafka auto-commit, the librdkafka default: positions are stored as messages are
handed to the application and committed every auto.commit.interval.ms. ack and
nack are advisory no-ops; a crash can lose the tail of processed-but-uncommitted work
or skip unprocessed deliveries that were already stored.
Per-message acknowledgement: enable.auto.offset.store is switched off and an ack
advances the stored position to just below the lowest still-unsettled delivery (or to
the highest delivered offset once none are outstanding). At-least-once stays precise
with concurrent handler lanes, and offset gaps the consumer never receives (transaction
markers, compacted-away records) cannot block the position. Auto-commit still flushes
the stored position in the background and once more when the consumer closes.