NativeAck endpoint mode for Pulsar (must force individual acks)

[jeremydmiller]

Adopter issue from the #3715 triage. Carries a correctness trap — read before starting.

The trap

The #3715 starting analysis called Pulsar "straightforward" because individual acks are supported. Verification says otherwise: PulsarListener.CompleteAsync (src/Transports/Pulsar/Wolverine.Pulsar/PulsarListener.cs:278) does not ack directly — it delegates to _ackHandler.CompleteAsync(...), and the ack strategy is configurable per #3180, including cumulative.

A cumulative ack is precisely the defect that disqualifies Kafka. Under EndpointMode.NativeAck the execution block completes messages in handler-completion order, not delivery order, so a cumulative ack of a later message would silently settle every earlier in-flight delivery — turning the mode's no-loss guarantee into silent loss. This is the same hazard #3706 fixed for RabbitMQ by making every ack multiple: false.

Note the retry-consumer path already acks individually unconditionally; it is the primary consumer's configurable strategy that is the problem.

Work

1. Decide and implement one of: force individual acks for a NativeAck endpoint regardless of the configured strategy, or reject the NativeAck + cumulative-ack combination at configuration time with a message naming both settings. Do not let the combination be configurable-and-silently-wrong — that is the exact failure Validate or warn on silently-ignored listener configuration combos (Inline + partitioning/parallelism) #3712 exists to prevent.
2. supportsNativeAck => true on the Pulsar endpoint once (1) is in place.
3. Mode-default tuning: receiver queue size as the prefetch equivalent, covering every lane that can be busy at once.
4. Check UseNativeRedelivery / negative-ack backoff interacts sanely with lane-based retry.
5. Flip this transport's line in the release-gate test; update the transport docs page.

Acceptance

• A test proving a cumulative-ack configuration cannot silently coexist with NativeAck.
• The EndpointMode.NativeAck: native broker acks with parallel + group-partitioned in-memory processing #3708 compliance expectations, including redelivery after a node dies mid-flight.

Parent: #3715. Mode: #3708.