fix sync --all failing when deleted branch exists in tree

[willschnicke-silkline]

WHY
av sync --all --rebase-to-trunk crashes with error: git merge-base: exit status 128 when a branch has been deleted from git but not yet cleaned up with av tidy. This happens because GetTargetBranches includes all branches from av's metadata DB without checking if the git refs still exist.

WHAT
added ref existence checks in GetTargetBranches for AllBranches mode — branches whose git refs no longer exist are silently skipped instead of being passed to the sequencer where they'd cause git merge-base to fail.

TESTING

• added e2e test that creates a deleted-but-not-tidied branch and verifies sync --all --rebase-to-trunk succeeds
• all existing sync and restack e2e tests pass

[aviator-app]

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[aviator-app]

🔃 FlexReview Status

Common Owner: aviator-co/engineering (expert-load-balance assignment)
Owner and Assignment:

• 🔒 aviator-co/engineering (expert-load-balance assignment)
  • Slack: #av-slack-testing
  • Assigned: davi-maciel
  Owned Files

  • 🔒 e2e_tests/sync_all_deleted_branch_test.go
  • 🔒 internal/sequencer/planner/targets.go

Review SLO: 7 business hours if PR size is <= 200 LOC for the first response.

[gemini-code-assist]

Code Review

This pull request introduces a fix to prevent av sync --all from failing when a branch tracked in metadata has been deleted from Git. It includes an E2E test and updates GetTargetBranches to verify branch existence. The review feedback points out that errors from repo.DoesRefExist are ignored, which could lead to silent failures; handling these errors is recommended to ensure the tool behaves correctly during Git communication issues.

[gemini-code-assist]

The error returned by repo.DoesRefExist is being ignored. If DoesRefExist encounters an error (e.g., a problem communicating with Git), exists will be false, and the branch will be silently skipped. This can lead to incorrect behavior where branches are skipped due to an error rather than actual deletion. Errors should be handled explicitly, either by propagating them or logging them appropriately, to prevent silent failures.

ref := plumbing.NewBranchReferenceName(br.Name)
if exists, err := repo.DoesRefExist(ctx, ref.String()); err != nil {
	return nil, errors.Wrapf(err, "failed to check existence of branch %q", br.Name)
} else if exists {
	ret = append(ret, ref)
}

[gemini-code-assist]

Similar to the previous comment, the error returned by repo.DoesRefExist is ignored here. This can lead to branches being incorrectly skipped if there's an underlying issue with Git communication, rather than the branch truly not existing. It's important to handle errors explicitly to ensure the correct behavior of the sync --all operation.

ref := plumbing.NewBranchReferenceName(n)
if exists, err := repo.DoesRefExist(ctx, ref.String()); err != nil {
	return nil, errors.Wrapf(err, "failed to check existence of branch %q", n)
} else if exists {
	ret = append(ret, ref)
}