Apply share_labels/target_info tags regardless of payload order

[ian28223]

What does this PR do?

Fixes LabelAggregator (OpenMetrics V2) so share_labels/target_info tags are collected from the full scrape payload before any metric is yielded, instead of interleaving collection with yielding.

Motivation

• If the shared-label source metric appears after a counter in the payload, that counter is yielded untagged on the first scrape, then tagged on every scrape after.
• For a monotonic counter, that tag change looks like a brand new context, and combined with the scraper's flush_first_value flag already being True by the second scrape, its full raw counter value gets flushed as a single interval's delta instead of a small diff.
• Root-caused via a RabbitMQ customer escalation (rabbitmq.queue.messages.acked.count spiking to the counter's entire lifetime total on Agent restart); reproduces identically on the generic openmetrics check, confirming it's a base-check issue.

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• Add qa/required if this PR needs QA validation, or qa/skip-qa if it does not. Exactly one of the two is required.
• If you need to backport this PR to another branch, you can add the backport/<branch-name> label to the PR and it will automatically open a backport PR once this one is merged

[datadog-prod-us1-5]

 

🎉 All green!

🧪 All tests passed
❄️ No new flaky tests detected

🎯 Code Coverage (details)
• Patch Coverage: 100.00%
• Overall Coverage: 88.63% (+0.10%)

_{This comment will be updated automatically if new data arrives.
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[cit-pr-commenter-54b7da]

evalya-impact-summary

evalya impact analysis

Impact analysis: 0 selected, 0 skipped (of 0 test tasks)
Publish tasks:   1 (always emitted)
Diff (4 files):
  datadog_checks_base/changelog.d/24884.fixed
  datadog_checks_base/datadog_checks/base/checks/openmetrics/v2/labels.py
  datadog_checks_base/tests/base/checks/openmetrics/test_v2/scraper/test_http_status_class_scraper.py
  datadog_checks_base/tests/base/checks/openmetrics/test_v2/test_options.py

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[chatgpt-codex-connector]

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[dd-octo-sts]

Validation Report

All 21 validations passed.

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Validation	Description	Status
agent-reqs	Verify check versions match the Agent requirements file	✅
ci	Validate CI configuration and code coverage settings	✅
codeowners	Validate every integration has a CODEOWNERS entry	✅
config	Validate default configuration files against spec.yaml	✅
dep	Verify dependency pins are consistent and Agent-compatible	✅
http	Validate integrations use the HTTP wrapper correctly	✅
imports	Validate check imports do not use deprecated modules	✅
integration-style	Validate check code style conventions	✅
jmx-metrics	Validate JMX metrics definition files and config	✅
labeler	Validate PR labeler config matches integration directories	✅
legacy-signature	Validate no integration uses the legacy Agent check signature	✅
license-headers	Validate Python files have proper license headers	✅
licenses	Validate third-party license attribution list	✅
metadata	Validate metadata.csv metric definitions	✅
models	Validate configuration data models match spec.yaml	✅
openmetrics	Validate OpenMetrics integrations disable the metric limit	✅
package	Validate Python package metadata and naming	✅
qa-label	Validate the pull request declares whether it needs QA for the next Agent release	✅
readmes	Validate README files have required sections	✅
saved-views	Validate saved view JSON file structure and fields	✅
version	Validate version consistency between package and changelog	✅

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