fix(go): back off before re-polling failed batch

[NikolayS]

Bug

In clients/go/consumer.go, the consumer loop slept pollInterval only on receive error or empty batch. When a batch WAS received but finalization failed — nackFailed true (loop did continue with no sleep) or Ack returned an error (fell through to the loop top with no sleep) — the loop re-polled immediately. Because the batch was never finished, pgque.next_batch returns the SAME batch instantly, so a persistent nack/ack failure (e.g. partial grants where receive works but nack/ack don't) produced a tight loop at full speed: re-receive same batch, re-run all handlers (duplicate side effects), fail again, repeat. Even one transient ack failure re-executed the whole batch's handlers with zero delay.

Fix

Sleep pollInterval (respecting ctx cancellation, same select { case <-ctx.Done() ... case <-time.After(...) } pattern used in the receive-error and empty paths) before re-polling on both the nack-failure path and the Ack-error path. The Ack n==0 stale/double-ack case stays warning-only and gains no sleep.

Red/green TDD: added TestConsumer_NackFailure_BacksOffBeforeRepoll and TestConsumer_AckFailure_BacksOffBeforeRepoll with a stub backend (redeliverStubBackend) whose Receive always returns the same batch and whose Nack/Ack fail; the tests bound the number of Receive calls in a 400 ms window with a 50 ms poll interval.

Verification

Red (on unfixed code, go test -run BacksOffBeforeRepoll ./... in clients/go):

--- FAIL: TestConsumer_NackFailure_BacksOffBeforeRepoll (0.45s)
    Receive called 52141 times in 400ms with pollInterval 50ms — tight re-poll loop on nack failure (want <= 11)
--- FAIL: TestConsumer_AckFailure_BacksOffBeforeRepoll (0.58s)
    Receive called 236297 times in 400ms with pollInterval 50ms — tight re-poll loop on ack failure (want <= 11)

Green (with fix, in clients/go):

$ go test ./...
ok  	github.com/NikolayS/pgque-go	4.784s
?   	github.com/NikolayS/pgque-go/bench/coop_demo	[no test files]
$ go vet ./...
(clean, no output)

Addresses finding B1 (Go) of #283

https://claude.ai/code/session_01KAaEGkQZmey1D1xCsVGmqv

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Generated by Claude Code

[NikolayS]

samorev Code Review Report

• PR: fix(go): back off before re-polling failed batch #284 - fix(go): back off before re-polling failed batch
• Author: @NikolayS
• AI-Assisted: Unknown

Pipeline	Coverage
PASS	Not reported

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BLOCKING ISSUES (1)

HIGH MR/PR state - Review target is draft

The review target is still marked as draft.
Fix: Mark it ready for review before merge.

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Summary

Area	Findings	Potential	Filtered
CI/Pipeline	0	0	0
Security	0	0	0
Bugs	0	0	0
Tests	0	0	0
Guidelines	0	0	0
Docs	0	0	0
Metadata	1	0	0

Note:

• Findings: High-confidence issues (8-10/10) - blocking or non-blocking per severity
• Potential: Medium-confidence issues (4-7/10) - review manually
• Filtered: Low-confidence issues (0-3/10) - excluded as likely false positives

Review metadata

provider=github
kind=pr
project=NikolayS/PgQue
number=284
target=github:NikolayS/PgQue#284
state=OPEN
draft=true
diff_lines=174
diff_added=139
diff_removed=1
diff_bytes=6157
comments_count=0
commits_count=1
ci_status=success
ci_summary=total=14 success=14 failure=0 pending=0 other=0
prompt=.claude/commands/review-mr.md
blocking=false
posted_by=gh
no_comment=false
live_posting=posted

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samorev-assisted review (AI analysis by Tanya301/samorev)