Add config settings

[solababs]

Why

There is no configuration surface for controlling automatic branch deletion after merge. Without these settings, the feature cannot be safely rolled out — behavior needs to default to off and be explicitly opt-in.

This PR adds the two config flags that gate the feature, along with a dependency validator between them. It is Phase 1 of the full implementation plan.

What changed

• Added delete_branch_after_merge: bool (default false) to MainSettings — when enabled, the Infrahub branch is automatically deleted after a successful merge.
• Added delete_git_branch_after_merge: bool (default false) to MainSettings — when enabled, the corresponding Git branch is also deleted; requires delete_branch_after_merge to be enabled.
• Added a @model_validator that raises at startup if delete_git_branch_after_merge=true without delete_branch_after_merge=true, preventing a misconfigured state.
• Added 3 unit tests covering the defaults and the validation error.

No behavioral changes beyond the new config fields — no deletion logic is wired up yet.

Suggested review order

1. backend/infrahub/config.py — the two new fields and the validator
2. backend/tests/unit/test_config.py — unit tests

How to review

Focus on the validator logic in config.py — specifically whether the error message and validation mode (after) are appropriate. The rest is straightforward field additions.

No schema, API, or database changes in this PR.

How to test

# Run the new tests
uv run pytest backend/tests/unit/test_config.py -v -k "delete_branch"

# Full unit suite
uv run invoke backend.test-unit

Expected: all three new tests pass. Attempting to instantiate MainSettings(delete_git_branch_after_merge=True, delete_branch_after_merge=False) raises a ValidationError with the message requires 'delete_branch_after_merge' to be enabled.

Impact & rollout

• Backward compatibility: No breaking changes. Both settings default to false, so existing deployments are unaffected.
• Config/env changes: Two new optional settings in MainSettings: delete_branch_after_merge and delete_git_branch_after_merge.
• Deployment notes: Safe to deploy independently. The deletion logic is not implemented yet.

Checklist

• Tests added/updated
• Changelog entry added (uv run towncrier create ...)
• External docs updated (if user-facing or ops-facing change)
• Internal .md docs updated (internal knowledge and AI code tools knowledge)

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[codspeed-hq]

Merging this PR will not alter performance

✅ 12 untouched benchmarks

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_{Comparing sb-13032026-add-config-settings-ifc-2336 (b07039d) with stable (43d16b8)¹}

Footnotes

1. No successful run was found on sb-13032026-delete-branch-after-merge-ifc-2336 (1ac1311) during the generation of this report, so stable (43d16b8) was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[ajtmccarty]

probably more of a design-level question, but it seems like we should be able to delete a branch on git regardless of whether the branch is being automatically deleted after a merge or manually deleted later

[solababs]

@ajtmccarty as seen here #8431 (comment), i think this was intentionally designed this way