(2.14) [IMPROVED] Only allocate AckAll sequences when acking in place

[MauriceVanVeen]

Follow-up of #8431

[synadia-claude-reviewer]

Claude finished @MauriceVanVeen's task in 1m 5s —— View job

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Code Review

• Gather PR diff and context
• Review changed code in server/consumer.go
• Verify correctness of guard condition
• Post findings

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Summary

Clean, correct optimization. The change guards the ackAllSeqs slice allocation behind if ackInPlace, preventing a heap allocation that was always wasted when ackInPlace == false.

Why it's safe:

All uses of ackAllSeqs were already gated on ackInPlace:

1. Write path (server/consumer.go:3823): if ackInPlace && seq != sseq { ackAllSeqs = append(...) } — the slice is never written unless ackInPlace is true.
2. Read path (server/consumer.go:3859-3863): if ackInPlace { for _, seq := range ackAllSeqs { ... } } — the slice is never iterated unless ackInPlace is true.

So before this fix, make([]uint64, 0, ...) was called unconditionally for every AckAll/AckFlowControl ack, but the resulting slice was immediately discarded whenever ackInPlace == false (i.e., for all clustered consumers or LimitsPolicy retention). This is the hot path for cumulative acknowledgment — skipping the allocation is a meaningful win.

Capacity bound is sound: sgap = sseq - o.asflr. The early sseq <= o.asflr check at line 3804 guarantees sgap >= 1, so sgap - 1 >= 0 — no underflow.

No issues found. LGTM.

[neilalexander]

LGTM