Let the fire slot serialize the metered review and nothing else

[kristofferR]

Roadmap item F2: the queue exists for one thing, and this makes the code say so.

The bug

Pump returned as soon as it had progressed the round holding the fire slot:

if slot := st.SlotRound(); slot != nil {
    return s.progressSlotRound(ctx, *slot)   // ← pump over
}

Further down, the bounded rescue scan guarded itself with

if decision.Verdict == engine.FireNo && (accountBlocked || !global.SlotFree) {

so it claimed to cover both starvation causes. The !global.SlotFree half had never executed
once — control cannot reach that line with the slot held. A summary-only round, whose CodeRabbit
review is never coming at all, therefore stayed queued for as long as an unrelated PR's review ran.

TestWaitResolvesSummaryOnlyWithoutTheQueue documented the short-circuit and routed around it in
Wait; nothing fixed it in the pump.

The rule

The fire slot serializes one account-metered review. The account window bounds that same
allowance. Neither has any authority over a round that spends no quota — a co-reviewer defer, a
dedupe, a summary-only round.

So progressing the slot round no longer ends the pump. It reloads state (progressing may have
released the slot) and sweeps the quota-free rounds behind it. A pump still never both progresses
and fires, because a quota-free verdict is not a fire, takes no slot, and posts no
@coderabbitai review.

The scan is now one sweepQuotaFree called from both paths that can starve, instead of a loop
inlined into the tail of the account-blocked case — which is how one of its two callers came to be
unreachable in the first place. The scan budget and the rotating start survive unchanged; they are
cost control, and the rotation still answers the case where the rounds behind the head all need
CodeRabbit.

Verification

TestPumpSweepsQuotaFreeRoundWhileTheSlotIsHeld stages it directly: an unrelated PR holds the slot,
a summary-only round is queued behind it, one Pump must move it. Confirmed to fail on main
(the summary-only round must move while the slot is held ... Phase:"queued") and pass here. It also
asserts the slot still belongs to the holder afterwards and that no CodeRabbit command was posted —
otherwise "it moved" could mean it moved by spending the very quota it must not.

gofmt -l . clean, go vet ./... clean, go test ./... -count=1 green across all six packages.

Ref #42

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Review details

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Configuration used: Organization UI

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Run ID: 8e0d25a1-40fd-407c-bd26-e6fa5624cb7c

📥 Commits

Reviewing files that changed from the base of the PR and between 03c7d2e and 3a7e271.

📒 Files selected for processing (2)

• internal/crq/service.go
• internal/crq/service_test.go

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/budget-gates-the-queue

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[kristofferR]

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