fix(backend): abort GitLab sync on non-404 API errors to prevent repo deletion

[brendan-kellam]

Summary

• GitLab API errors (e.g. 500) were previously converted to warnings, allowing the sync to continue with a partial repo list
• The database reconciliation then deleted all RepoToConnection records and only re-created repos from the partial list, effectively orphaning repos from the failed group/user/project
• Now only 404 errors are treated as warnings (resource not found or no access); all other errors abort the sync so the database is left untouched — matching the existing behavior in github.ts

Fixes #1029

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes
  • Fixed GitLab sync to preserve repositories when the API encounters non-404 errors. The sync now correctly handles only "not found" scenarios without unexpected repository deletion.

[coderabbitai]

Caution

Review failed

The pull request is closed.

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: c6ddd68a-da1d-43f7-9a45-18639f37c2e8

📥 Commits

Reviewing files that changed from the base of the PR and between bdab4b7 and c5c1734.

📒 Files selected for processing (2)

• CHANGELOG.md
• packages/backend/src/gitlab.ts

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Walkthrough

Fixed GitLab API error handling to prevent unintended repository deletion when non-404 errors (e.g., HTTP 500) occur during group/user/project lookups. The code now distinguishes between 404 errors (treated as warnings) and other errors (rethrown), preventing silent fallthrough that caused data loss.

Changes

Cohort / File(s)	Summary
Changelog Documentation CHANGELOG.md	Added entry documenting the fix that prevents repository deletion when GitLab API returns non-404 errors during sync operations.
Error Handling Logic packages/backend/src/gitlab.ts	Refined GitLab API error handling in getGitLabReposFromConfig to specifically check for 404 status and return a warning result with descriptive messages (e.g., "Group not found or no access"). Non-404 errors are rethrown instead of being silently ignored, preventing unintended repository deletion during API failures.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch brendan/fix-SOU-727

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