ci: forward CUOPT_SLACK_MENTION_ID secret to nightly-summary

[rgsl888prabhu]

Summary

• Declare CUOPT_SLACK_MENTION_ID as an optional workflow_call secret on the reusable nightly-summary workflow and forward it to the run-step env.
• Pass it from test.yaml to the nightly-summary job alongside the other Slack secrets.

Why

ci/nightly_summary.sh already forwards CUOPT_SLACK_MENTION_ID to ci/utils/generate_slack_payloads.py, which uses it to prefix <@id> mentions on new failures and new flaky tests. Until now the env var was never populated in CI, so the mention was always empty. With this change, setting the CUOPT_SLACK_MENTION_ID repo secret (Slack user ID like U01ABCDEF or group handle like S01ABCDEF) will ping the configured handle. Leaving it unset preserves the no-mention default.

Test plan

• Add CUOPT_SLACK_MENTION_ID repo secret.
• Trigger a nightly run (or workflow_dispatch on nightly-summary) and confirm the Slack message includes the <@id> mention on new failures.
• Verify behavior is unchanged when the secret is unset (no mention).

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Enterprise

Run ID: 08f9ef76-184a-4816-a328-b0deec71530e

📥 Commits

Reviewing files that changed from the base of the PR and between 733a459 and 26d3221.

📒 Files selected for processing (2)

• .github/workflows/nightly-summary.yaml
• .github/workflows/test.yaml

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📝 Walkthrough

Walkthrough

Two GitHub Actions workflow files are updated to introduce a new optional secret CUOPT_SLACK_MENTION_ID, making it available to the nightly summary job and environment.

Changes

Slack Mention Secret Integration

Layer / File(s)	Summary
Secret Definition & Environment Setup .github/workflows/nightly-summary.yaml	New optional secret CUOPT_SLACK_MENTION_ID is declared and exported to the Run nightly summary step environment.
Job Secret Wiring .github/workflows/test.yaml	Secret mapping for CUOPT_SLACK_MENTION_ID is added to the nightly_summary job.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~5 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately summarizes the main change: forwarding the CUOPT_SLACK_MENTION_ID secret to the nightly-summary workflow, which directly reflects the modifications across both workflow files.
Description check	✅ Passed	The description comprehensively explains the changes, including the what, why, and how the CUOPT_SLACK_MENTION_ID secret is being integrated into the CI workflows, with a clear test plan.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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