ci: reduce required scope checkout transfer

[henrypark133]

Summary

• Reduce transfer in the two required-check scope jobs without changing their path-selection policy.
• Keep full commit ancestry where three-dot diffs need a merge base, but omit historical blobs with checkout's partial-clone filter.
• Use a depth-1 checkout for Tests (Reborn) events that always build the exhaustive plan and never inspect a diff.
• Add a contract that pins both the transfer optimization and the existing three-dot diff semantics.

Change Type

• CI/Infrastructure

Linked Issue

Related #7799. This is the smaller replacement experiment after closing the nextest/matrix approach in #7817.

Validation

• Relevant tests pass: planner and WS12 workflow contracts
• If a coding agent was used and supports it, pr-shepherd was run before requesting review

Test Strategy

User behavior: PR and merge-queue lane selection is unchanged; scope checkout should become faster and less variable.

Risk areas:

• Cross-component behavior

Tests added or updated:

• Unit or contract: test_scope_checkouts_minimize_transfer_without_losing_pr_ancestry
• Reborn integration: Not applicable: no Rust/runtime behavior changes.
• Recorded fixture: Not applicable: no model-visible behavior changes.
• Browser E2E: Not applicable: no UI changes.
• Backend or runtime: Not applicable: workflow checkout inputs only.
• Live canary: Not applicable: no deployed behavior changes.

What the tests prove: both required scope jobs use blobless partial clone, the Tests planner uses depth 1 only outside pull requests, and both jobs retain their three-dot diff.

Commands run:

python3 scripts/ci/test_reborn_pr_test_plan.py
python3 scripts/ci/ws12_workflow_contracts.py
python3 scripts/ci/test_ws12_workflow_contracts.py
python3 -m unittest scripts.ci.test_reborn_pr_test_plan.RebornPrTestPlanTests.test_scope_checkouts_minimize_transfer_without_losing_pr_ancestry
python3 yaml.safe_load for both changed workflows
git diff --check

Security Impact

None. Repository permissions and persist-credentials: false are unchanged.

Reborn Trust-Boundary Checklist

N/A: CI checkout transfer only; no product trust boundary changes.

Database Impact

None.

Blast Radius

The changes jobs in the two required workflows. A checkout implementation incompatibility would fail scope detection before any test or lint matrix runs; no check is silently skipped.

Compatibility: actions/checkout v6 supports the filter input. Pull requests and Code Style merge-group runs retain fetch-depth: 0, so merge-base ancestry and base-lockfile reads remain available. Non-PR Tests events already select the exhaustive plan and do not read diff history.

Measurement: compare checkout and total changes duration on this PR and its merge-group run against the recent observed 1.1–6.0 minute scope range. This slice is successful if selection stays identical and checkout variance materially contracts; it is not claimed by itself to deliver the complete sub-10-minute CI target.

Rollback Plan

Revert this commit. That restores fetch-depth: 0 without partial clone in both scope jobs. Because the change is confined to checkout inputs and fails before lane fan-out, rollback requires no data migration or compatibility window.

Review Follow-Through

Please require two approvals for this Track C workflow change. After PR CI, record the scope-job checkout timings before considering the next runner-capacity slice.

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Review track: C

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.

[railway-app]

🚅 Deployed to the ironclaw-pr-7894 environment in ironclaw-ci-preview

Service	Status	Web	Updated (UTC)
ironclaw	✅ Success (View Logs)	Web	Aug 25, 2026 at 8:25 pm

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: ASSERTIVE

Plan: Pro Plus

Run ID: 45c72b20-95e3-4f38-a9ff-8cbb539fcf1f

📥 Commits

Reviewing files that changed from the base of the PR and between 5e489d4 and b251075.

📒 Files selected for processing (3)

• .github/workflows/code_style.yml
• .github/workflows/reborn-tests.yml
• scripts/ci/test_reborn_pr_test_plan.py

Included review availability: Your plan provides up to 10 included reviews per hour; 9 remain after this review.

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📝 Walkthrough

Summary by CodeRabbit

• Performance

  • Reduced unnecessary data downloaded during automated validation checks by using optimized repository checkouts.
  • Preserved accurate pull request change comparisons while minimizing transfer size.

• Tests

  • Added coverage to verify that optimized checkouts retain the required pull request comparison behavior.

Walkthrough

CI workflows now use blobless checkouts and event-specific fetch depth. Pull-request ancestry remains available for three-dot scope diffs. A contract test verifies these checkout settings.

Changes

CI checkout efficiency

Layer / File(s)	Summary
Checkout transfer and ancestry rules .github/workflows/reborn-tests.yml, .github/workflows/code_style.yml, scripts/ci/test_reborn_pr_test_plan.py	Reborn uses full history for pull requests and shallow history for other events, with blob:none for all events. Code Style enables blob:none while retaining the ancestry required for three-dot diffs. A contract test verifies these settings.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: ⚪ Minimal · up to b2510

This PR reduces CI checkout transfer while preserving existing scope-selection behavior and three-dot diff semantics; no actionable merge-blocking risk remains beyond normal checks and review.

Suggested reviewers: benkurrek

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly describes the CI checkout-transfer optimization and uses the Conventional Commits ci: prefix. The missing scope is acceptable because the requirement states a preference, not a man…
Description check	✅ Passed	The description is complete and directly matches the workflow and contract-test changes. It covers the required summary, change type, issue, validation, test strategy, security, trust boundary, databa…
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.

Full details: Title check

Explanation

The title clearly describes the CI checkout-transfer optimization and uses the Conventional Commits ci: prefix. The missing scope is acceptable because the requirement states a preference, not a mandatory format.

Full details: Description check

Explanation

The description is complete and directly matches the workflow and contract-test changes. It covers the required summary, change type, issue, validation, test strategy, security, trust boundary, database impact, blast radius, rollback, review follow-through, and review track.

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[ironloopai]

Review · Status

🟩 Completed

IronLoop completed the review and posted it to GitHub.

Result

Open submitted review →

Run details

• Run: b65691ed-c1d8-412d-82ae-4b357fdc06b5
• Base: main at 5e489d4
• Head: ci/scope-checkout-transfer at b251075
• Created: 2026-08-25 20:29 UTC
• Updated: 2026-08-25 20:35 UTC

_{Automatic trigger · attempt 1 of 3 · completed in 5m 52s}

[henrypark133]

First-run measurement (PR event, commit b251075):

• Code Style scope job: 23s total; checkout 11s; runner start ~3s after workflow creation.
• Tests scope job: 47s total; checkout 12s; runner start ~4s after workflow creation.
• Required Code Style workflow: green in ~4m03s from workflow creation.
• Required Tests (Reborn) workflow: green in ~9m00s from workflow creation.
• All checks: green; no review findings. Copilot could not review because its requester quota was exhausted.

This is a meaningful contraction from the recently observed ~1.1–6.0m scope range, with three-dot diff selection preserved. It proves the PR-event slice on this CI-only diff. We still need the merge-group run—and later a representative Rust PR—to assess queue predictability and the broader p90 target.

[ironloopai]

Review · Summary

🟢 No actionable findings

No actionable issues found in the checkout-transfer changes.

Validation

• ✅ Scope checkout contract — The focused contract test passed for blobless checkout and PR ancestry settings.
• ✅ Reborn planner contracts — The planner contract suite passed (92 tests).
• ✅ Workflow contracts — The workflow contract checker and its 156-test suite passed.
• ✅ Workflow YAML — Both changed workflow files parsed successfully.

Review details

• Run: b65691ed-c1d8-412d-82ae-4b357fdc06b5
• Attempts: 1

[lloydmak99]

The checkout changes preserve full ancestry where PR scope detection needs it and use shallow checkout only for events that build the exhaustive plan. No blocking issues found.

Checks: 92 planner tests, 156 workflow contract tests, focused checkout-scope test, YAML parsing for both workflows, and git diff --check all passed.