[speriaswamy-amd]

Motivation

The coco PR gate built its develop baseline at develop tip on every run, because each run uses a fresh output directory. A PR was therefore measured against code it did not contain. In 18 replayed ruby64 runs, seven unrelated PRs showed another commit's 1-node reduce_scatter change (#12928) as their own.

Technical Details

rccl_resolve_coco_run.py now, for PR runs:

• resolves the PR's base branch (GET /pulls/{n}) and its merge-base with the head (GET /compare/{base}...{head}), using the job's GITHUB_TOKEN;
• appends --baseline-sha <merge-base> to coco_args, which already flows into both the build-only and the test coco pr calls;
• passes the flag only when the checked-out coco harness supports it (coco pr --baseline-sha, ROCm/tRCCL), and otherwise emits a workflow warning. This change is therefore safe to land before the harness release that adds the flag;
• fails the setup job when the merge-base cannot be resolved or equals the PR head, rather than silently comparing the wrong code.

Periodic runs are unchanged. The flag ships in coco 1.4, so pinning starts when the gate's default coco_ref moves from 1.3.x to 1.4.x. Until then, runs log the warning and behave as today.

Issue Tracking

JIRA ID: AICOMRCCL-2204

Test Plan

• Unit tests in .github/scripts/tests/rccl_resolve_coco_run_test.py (21 pass):
  • args with and without a pin;
  • merge-base resolution against the PR's own base branch;
  • refusal of a head that is its own merge-base, and of a malformed SHA;
  • periodic runs;
  • an older harness without the flag.
• Formatted with the repo's black 26.5.1.
• Resolved a real PR's merge-base through the new code: ci(rccl): build device-api with rocSHMEM GIN #12752 → a22b7e7847, matching gh api compare.

Test Result

All pass. A ruby64 gate run on a PR, once the harness has the flag, should show --baseline-sha in the coco pr command line and an RCCL version line at the merge-base on the baseline stack.

Submission Checklist

• Look over the contributing guidelines at https://github.com/ROCm/rocm-systems/blob/develop/CONTRIBUTING.md.

[therock-pr-bot]

✅ All Policy Checks Passed

Check	Status	Details
📝 PR Description	✅ Pass	—
⛔ Forbidden Files	✅ Pass	—
🧪 Unit Test	✅ Pass	—
🚫 Draft PR	🔜 To Be Enabled	—
🚩 Feature Flag	🔜 To Be Enabled	—
📊 Code Coverage	🔜 To Be Enabled	—

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