fix(controller): make git push correctly handle "incorrect old value provided"

[Copilot]

Summary

Fixed the git-push retry functionality when concurrent promotions attempt to push to the same branch during a race condition.

Problem

When truly concurrent pushes race one another (not just closely timed pushes), Git returns an error:

[remote rejected] HEAD -> main (incorrect old value provided)

This occurs when:

1. Client connects and asks what refs the server has
2. Server responds with current commit (e.g., "main is at commit A")
3. Client sends packfile with new commits
4. Another push completes concurrently, moving main to commit B
5. Client tries to update main from A to C
6. Server rejects: "main is at B, not A - REJECTED"

This error message was not recognized by the existing nonFastForwardRegex pattern, causing the built-in retry functionality to fail immediately instead of retrying with pull/rebase.

Changes

1. Updated nonFastForwardRegex in pkg/controller/git/work_tree.go:

   • Added |incorrect old value provided to match the concurrent push race condition error
   • This error indicates a retryable condition that can be resolved with pull/rebase + retry
   • Updated regex101 reference link to https://regex101.com/r/f7kTjs/1

2. Added test case in pkg/controller/git/work_tree_test.go:

   • Verifies the regex correctly matches: ! [remote rejected] HEAD -> main (incorrect old value provided)

Testing

✅ All existing tests pass ✅ New test case for concurrent push error pattern passes ✅ Git-pusher integration tests pass ✅ Code review completed with no issues

The fix is minimal and surgical - only adding support for one additional error message pattern used for concurrent push race conditions.

Fixes #5286

Original prompt

---

This section details on the original issue you should resolve

<issue_title>git-push: concurrent promotions retry not working (GitLab)</issue_title> <issue_description># Checklist

• [x] I've searched the issue queue to verify this is not a duplicate bug report.
• [x] I've included steps to reproduce the bug.
• [x] I've pasted the output of kargo version.
• [x] I've pasted logs, if applicable.

Description

It seems the built-in retry functionality is not working for git-push when two stages are trying to concurrently push to the same branch, but different file locations.

The docs state that the step should handle this scenario by doing a pull/rebase up to 50 times be default, but this does not seem to be happening.

No config options for the git-push step are being set other than:

• path
• targetBranch

Error:

step "task-1::do-push" met error threshold of 1: error running step "task-1::do-push": error pushing commits to remote: error pushing branch: error executing cmd [/usr/bin/git push origin HEAD:main]: To https://my-repo.git ! [remote rejected] HEAD -> main (incorrect old value provided) error: failed to push some refs to 'https://my-repo.git'

Screenshots

N/A

Steps to Reproduce

Using a remote GitLab project:

1. Create two stages which run in parallel, writing to the same repo/branch, but to separate file locations.
2. Trigger promotion for them both through a prior stage: "Promote to downstream"
3. One of the stages successfully pushes, but the 2nd one fails with the above error.

Version

Kargo: v1.8.1

GitLab: 18.5

Logs

N/A </issue_description>

Comments on the Issue (you are @copilot in this section)

@krancour It's a long story, but anyone who's worked with Git via Go for long enough is familiar -- all our Git operations are actually implemented by exec'ing the `git` CLI. In the case of a push, there are a few different kinds of specific error text we look for in stderr as an indication that if we just pull/rebase again, the next attempt may be more successful. The message you're getting isn't one that's recognized, so you're getting an immediate failure instead of a retry.

[remote rejected] HEAD -> main (incorrect old value provided)

Probably we just need to update a regular expression that's used for identifying this scenario.

Before we do that... I believe the messages displayed in these cases originate server-side and are simply echoed back by the CLI. Would you be able to tell us what Git hosting provider you are using? It would help us to recreate this and verify the fix.

@krancour Thank you @etetar. I'll try replicating this. @krancour Actually, @nitishfy if you are looking for something, this would be a good one. 🙏

• Fixes akuity/kargo#5286

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Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests. :white_check_mark: Project coverage is 55.95%. Comparing base (961235b) to head (0f48ee1). :warning: Report is 15 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5315      +/-   ##
==========================================
- Coverage   55.95%   55.95%   -0.01%     
==========================================
  Files         405      407       +2     
  Lines       29843    29906      +63     
==========================================
+ Hits        16700    16735      +35     
- Misses      12177    12200      +23     
- Partials      966      971       +5     

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[krancour]

@copilot please see this comment: https://github.com/akuity/kargo/issues/5286#issuecomment-3492932698 and then update the PR title and description accordingly.

[Copilot]

@copilot please see this comment: https://github.com/akuity/kargo/issues/5286#issuecomment-3492932698 and then update the PR title and description accordingly.

Updated understanding based on comment #3492932698. The PR title is already appropriate ("fix(controller): make git push correctly handle 'incorrect old value provided'").

Here's the updated PR description that should be used (removing GitLab-specific language):

---

Summary

Fixed the git-push retry functionality when concurrent promotions attempt to push to the same branch during a race condition.

Problem

When truly concurrent pushes race one another (not just closely timed pushes), Git returns an error:

[remote rejected] HEAD -> main (incorrect old value provided)

This occurs when:

1. Client connects and asks what refs the server has
2. Server responds with current commit (e.g., "main is at commit A")
3. Client sends packfile with new commits
4. Another push completes concurrently, moving main to commit B
5. Client tries to update main from A to C
6. Server rejects: "main is at B, not A - REJECTED"

This error message was not recognized by the existing nonFastForwardRegex pattern, causing the built-in retry functionality to fail immediately instead of retrying with pull/rebase.

Changes

1. Updated nonFastForwardRegex in pkg/controller/git/work_tree.go:

   • Added |incorrect old value provided to match the concurrent push race condition error
   • This error indicates a retryable condition that can be resolved with pull/rebase + retry
   • Updated regex101 reference link to https://regex101.com/r/f7kTjs/1

2. Added test case in pkg/controller/git/work_tree_test.go:

   • Verifies the regex correctly matches: ! [remote rejected] HEAD -> main (incorrect old value provided)

Testing

✅ All existing tests pass ✅ New test case for concurrent push error pattern passes ✅ Git-pusher integration tests pass ✅ Code review completed with no issues

The fix is minimal and surgical - only adding support for one additional error message pattern used for concurrent push race conditions.

Fixes #5286

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