Missing base commit on main despite earlier covered ancestors

[nikosatwork]

Describe the bug

On main commits in a merge-heavy history, Codecov intermittently shows Missing base commit even though earlier covered ancestors exist in git history and in Codecov. This causes parent lookup/carryforward to fail for some head commits.

Environment

• Browser: Chrome (used to verify in Codecov UI)
• System: GitHub Actions + public GitHub repo + public Codecov

To Reproduce

Steps to reproduce the behavior:

1. Clone/fork the public repro repository: https://github.com/nikosatwork/codecov-base-commit-test.
2. In GitHub Actions, run CI with Test Suite = Both (Runs core and ext test suites & uploads to Codecov with core and ext flags respectively).
3. Inspect the upload in Codecov (works as expected).
4. Run Create Stress Batch PRs with count=10.
5. Run Merge Batch PRs.
6. Run CI with Test Suite = Core.
7. Inspect the upload in Codecov: no base-commit error, and ext flag is carried forward as expected.
8. Run Create Stress Batch PRs again with count=40.
9. Run Merge Batch PRs.
10. Run CI with Test Suite = Core.
11. Inspect the upload in Codecov: Missing base commit error appears, and ext flag is not carried forward.

Expected behavior

Codecov should consistently resolve a valid base commit on main and carry forward ext flag from the nearest valid covered ancestor, regardless of merge-batch size (10 PRs vs 40 PRs).

Actual behavior

After the larger stress batch (40 PRs), running Core-only CI results in Missing base commit, and the ext flag is not carried forward. The smaller batch (10 PRs) does not show this failure.

• Inspect in Codecov here

Additional context

• See main-full-graph.txt, output of git --no-pager log --graph --oneline --decorate --max-count=200 main, showing the full commit graph around the relevant main heads.

  • ad4d07954ba9a187b25c134ba33e9911a58b7078 - initial commit and upload - Missing base commit expected - view in Codecov here
  • 5c09c9921e187828946de5034aea4aaac647182f - Upload after first 10-batch PRs landed - Shows correctly, base commit found - ext flag is carried forward - view in Codecov here
  • edef8d914d8e5e7829f87365cb0d2f25935d242b - Upload after second 40-batch PRs landed - Shows Missing base commit - ext flag is not carried forward - view in Codecov here

• Reproduced in public GitHub + public Codecov.

• Repository: https://github.com/nikosatwork/codecov-base-commit-test

• Codecov: https://app.codecov.io/github/nikosatwork/codecov-base-commit-test

• Pattern is intermittent and correlates with merge-heavy batches + partial/intermittent flag uploads.

• Not a broken git graph: affected commits have valid covered ancestors on main.

[linear]

CCMRG-2065

[nikosatwork]

Hi @drazisil-codecov @spalmurray @thomasrockhu-codecov - following up on #860, I've now reproduced the same behavior in a minimal public repo on app.codecov.io (with clear repro steps and expected/actual results in this issue). I also prototyped a worker-side fix in umbrella that appears to address the failure.

Could you advise on the best path to get those code changes reviewed and into product (apart from the guidelines here)? I’d really appreciate your guidance. Thank you!

[aerickson]

Currently experiencing this. I just develop on main for the project.

@nikosatwork what's the fix (I couldn't find anything by you in the umbrella repo)? Thanks.

[nikosatwork]

Hi @drazisil-codecov @spalmurray @thomasrockhu-codecov - quick follow-up on this issue.

I’ve opened a candidate fix in umbrella: codecov/umbrella#724
It targets the default-branch parent fallback path and includes focused tests tied to this repro.

Would you mind taking a look when you have a chance, or routing it to the right reviewer/team?
Happy to provide any extra logs, repro runs, or context needed to speed review. Thank you!