ci: centralize PR test classification in pr-test-summary (follow-up to #1194)

[ramakrishnap-nv]

Background

PR #1194 adds a per-failure classifier for PR test results, post­ing a sticky comment that splits failures into NEW (likely introduced by this PR) vs. KNOWN (recurring/flaky on nightly). To do that classification, each per-matrix test container sources ci/utils/nightly_report_helper.sh in PR mode, downloads the target branch's nightly failure history from S3, and uploads its own per-matrix summary back to a PR-scoped S3 prefix. The pr-test-summary job then aggregates those summaries into the sticky comment.

That works, but it has two architectural awkwardnesses:

1. Load-bearing fallback for the target branch. GHA leaves github.base_ref empty for push events, and the PR workflow triggers on push to pull-request/[0-9]+ branches (the copy-pr-bot pattern). The rapidsai shared test workflows don't propagate a target branch into the test container, so the helper currently uses ${GITHUB_BASE_REF:-${RAPIDS_BRANCH:-main}} to recover one. See the inline comment at ci/utils/nightly_report_helper.sh:115.
2. S3 write surface in every PR test container. Each test container needs CUOPT_AWS_* credentials so it can upload its per-matrix summary.

Proposal: centralize PR classification in pr-test-summary

The pr-test-summary job already resolves the target branch via the GitHub API (it has to, in order to render the comment). If we move classification there, both awkwardnesses disappear.

Sketch:

	Current (distributed)	Proposed (centralized)
Per-matrix test job	Sources nightly_report_helper.sh in PR mode, downloads nightly history, classifies, uploads per-matrix summary to S3	Just produces JUnit XML — uploaded as a workflow artifact (actions/upload-artifact)
pr-test-summary	Downloads classified summaries from S3, aggregates, posts	Downloads JUnit XML artifacts, resolves target branch, runs nightly_report.py --mode pr per matrix against the resolved branch's history, aggregates, posts
CUOPT_AWS_* write secrets in test containers	required	not required
${GITHUB_BASE_REF:-${RAPIDS_BRANCH:-main}} fallback	required	removed
nightly_report_helper.sh PR-mode branch	present	removed

Work items

• Verify whether the rapidsai shared test workflows (conda-python-tests.yaml, wheels-test.yaml, the custom one used by test-self-hosted-server) already upload RAPIDS_TESTS_DIR/*.xml as workflow artifacts, and confirm the artifact-name convention so pr-test-summary can find them. If they don't, add an actions/upload-artifact step (probably in ci/test_*.sh or as a new workflow step).
• Refactor pr-test-summary (in .github/workflows/pr_test_summary.yaml and ci/pr_summary.sh):
  • Download every test job's JUnit artifacts.
  • For each (test_type, matrix_label) tuple, invoke nightly_report.py --mode pr pointing at the right s3://.../ci_test_reports/nightly/history/{branch}/{test_type}-{matrix}.json.
  • Aggregate and post (existing renderer is unchanged).
• Remove the PR-mode branch in ci/utils/nightly_report_helper.sh and the now-unused mode="pr" paths through the helper.
• Drop CUOPT_AWS_* secrets from PR test job callers in .github/workflows/pr.yaml.
• Confirm nightly mode is byte-identical in behavior after the change (the helper's nightly branch is untouched by the refactor itself, but the file diff should be reviewed).

Why not in PR #1194

PR #1194 is already large (classifier + renderer + comment poster + workflow wiring + several review iterations). The architecture refactor changes a different axis (where classification runs) and is best kept isolated so its review can focus on the workflow / artifact mechanics rather than on the comment content.

[github-actions]

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[github-actions]

🔔 Hi @anandhkb @ramakrishnap-nv, this issue has had no activity for 21 days. Please update or let us know if it can be closed. Thank you!

If this is an "epic" issue, then please add the "epic" label to this issue.
If it is a PR and not ready for review, then please convert this to draft.
If you just want to switch off this notification, then use the "skip inactivity reminder" label.