fix: TRAC-1072 Seed idle queue gauges at zero instead of deleting

[chanceaclark]

Pull Request Template

Description

Follow-up to #19, which fixed cloudflare_queue_backlog_messages and related gauges freezing at a stale non-zero value by calling DeletePartialMatch({"account": accountName}) on all 7 queue gauges in fetchQueueAnalytics before repopulating them each scrape.

That overcorrected: a queue that's idle most of the time will have no rows in Cloudflare's queueBacklogAdaptiveGroups/queueConsumerMetricsAdaptiveGroups responses, since those endpoints only emit rows for queues with activity in the scrape window. The delete-then-rebuild wiped the series on every idle scrape and it never got repopulated, so downstream dashboards showed no data at all for hours at a stretch instead of a correct zero baseline. Confirmed in production: after the #19 deploy, an idle queue's backlog/concurrency series had one brief real reading, then many hours of zero data points, while the exporter itself stayed healthy and scraping normally.

Fix: for the 3 gauges keyed only by queue_name/account (queueBacklogMessages, queueBacklogBytes, queueConsumerConcurrency), seed every currently known queue (from fetchQueueNames) at 0 immediately after the DeletePartialMatch calls and before applying this scrape's real values. Idle queues now read a continuous 0 instead of disappearing. The 4 operation-metric gauges (queueOperations, queueOperationBytes, queueOperationLagTime, queueOperationRetryCount) keep the delete-only behavior, since their action_type/outcome label combinations aren't enumerable ahead of time the way queue_name is.

Jira: TRAC-1072

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Code refactoring
• Other (please describe):

Testing

• I have run make pr-tests and all tests pass
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

go build ./... and gofmt -l . are clean, and the pre-commit golangci-lint hook passed. make pr-tests's test target (run_e2e.sh) requires live Cloudflare API credentials via .env and venom, not run here.

Manual verification post-deploy: watch a normally-idle queue's cloudflare_queue_backlog_messages/cloudflare_queue_consumer_concurrency series — it should read a continuous 0 during idle periods instead of showing gaps or a stuck non-zero value.

Code Quality

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation

Additional Notes

Requires a downstream rebuild/redeploy trigger once this merges.