[DO NOT MERGE] Tests for reorg auto-fix 3-way patching strategy

[hestonhoffman]

What does this PR do? What is the motivation?

Adds tests that verify the auto-fix patching strategy in resolve_pr_conflicts.py — specifically the format-patch → transform_diff_paths → git am --3way pipeline in attempt_fix().

This came out of a code review of the reorg scripts. The open question was whether --3way is the right merge approach, and in particular whether rewriting the patch's file paths (content/en/... → hugo/content/en/...) breaks --3way's ability to reconstruct the ancestor blob it needs. It does not — --3way keys the blob lookup on the SHA in the patch header, which the path rewrite leaves untouched.

astro_reorg/test_transform_diff_paths.py builds a throwaway git repo in a temp dir for each scenario (nothing in the real repo is touched) and covers three cases on the same pipeline:

1. Context drift, no overlap — --3way merges both the PR's edit and an unrelated master edit.
2. Control — the same patch fails under plain am (no --3way), proving --3way is load-bearing, not incidental.
3. True content conflict — PR and master edit the same line; --3way fails and git am --abort recovers, confirming attempt_fix() routes to manual review instead of pushing a silently-wrong branch.

Run with: python3 astro_reorg/test_transform_diff_paths.py

Merge instructions

This PR targets the jen.gilbert/astro-reorg-scripts branch, not master. It is for the author to review the tests — do not merge.

Merge readiness:

• Ready for merge

Additional notes

Not tied to a Jira ticket — this is review-support tooling for the reorg scripts.

🤖 Generated with Claude Code

[datadog-official]

⚠️ Warnings

🚦 2 Pipeline jobs failed

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