feat(git): track request source branch as upstream on checkout

[skevetter]

Summary

CheckoutPR fetches a pull/merge request into a synthetic MR<N>/PR<N> local branch with no upstream, so the local branch does not reference the remote branch the request was opened from (git status shows no tracking relationship).

After checkout, this resolves the origin branch whose tip matches the request head and sets it as the local branch's upstream. Because the head ref (refs/{pull,merge-requests}/N/head) carries the tip commit but not the source branch name, the match is done by commit via git for-each-ref --points-at over the already-fetched refs/remotes/origin/* — no provider API, token, or network call required.

It degrades cleanly to the prior behavior (untracked branch) when the match can't be trusted:

• Fork-based requests — source branch isn't on origin
• Ambiguous matches — more than one origin branch points at the head (e.g. the default branch too)
• Shallow clones — other branches aren't fetched

Works identically for GitHub and GitLab (including self-hosted).

Adds TestRepoCheckoutPRTracksSourceBranch and TestRepoCheckoutPRAmbiguousSourceBranchLeftUntracked.

Summary by CodeRabbit

• Enhancements
  • Pull request checkouts now automatically track the originating remote branch when a unique match can be identified.
  • Branches remain untracked when the source branch cannot be determined unambiguously.
• Bug Fixes
  • Improved pull request checkout behavior across supported Git providers while preserving existing fetch and switch workflows.

[netlify]

✅ Deploy Preview for images-devsy-sh canceled.

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✅ Deploy Preview for devsydev canceled.

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[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: fb93dd44-058f-4fd8-9692-33aababa735c

📥 Commits

Reviewing files that changed from the base of the PR and between c07b339 and 6514203.

📒 Files selected for processing (2)

• pkg/git/repo.go
• pkg/git/repo_test.go

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📝 Walkthrough

Walkthrough

CheckoutPR now best-effort tracks a uniquely resolved origin/* source branch after switching to a PR branch. Tests cover both unique source resolution and ambiguous matches, while other repository methods retain their behavior.

Changes

CheckoutPR source tracking

Layer / File(s)	Summary
Repository surface and command wrappers pkg/git/repo.go	Repository declarations, accessors, command wrappers, cloning helpers, and comments were reorganized without behavior changes.
Checkout source branch tracking pkg/git/repo.go, pkg/git/repo_test.go	CheckoutPR resolves a unique origin branch by revision and sets it as the local branch upstream; ambiguous matches leave the branch untracked, with both cases tested.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Possibly related PRs

• devsy-org/devsy#704: Both changes extend CheckoutPR handling for GitLab merge request references.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: tracking the request source branch as upstream during checkout.
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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