feat(digest): flag forks diverged from upstream - #5
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merge-upstream returns success whether it fast-forwards or produces a merge commit, so a series-named fork branch that someone accidentally pushed local commits to (e.g. merging a feature branch into 18.0) silently accumulates drift across daily syncs. ledoent/social:18.0 in May 2026 had grown 30 commits ahead before anyone noticed; today's run "succeeded" same as every prior one. Add a post-sync compare call per branch (when upstream_org is set in forks.yml) and surface ahead_by > 0 as a "Diverged from upstream" warning in the email — own section, separate subject tag, exit_marker unchanged so it stays informational and doesn't fail the workflow. Tests: divergence flagged with merge_type=merge + ahead_by>0, clean fast-forward not flagged, missing upstream_org skips the compare, compare-call failure doesn't mask a successful sync.
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Why
merge-upstream(the API behind GitHub's green "Sync fork" button) returns success whether it fast-forwards or produces a merge commit. So a series-named fork branch that someone accidentally pushed local commits to silently accumulates drift across daily syncs, and the digest reports "Synced" same as a healthy run.Concrete case from today:
ledoent/social:18.0had grown 30 commits ahead ofOCA/social:18.0before anyone noticed — caused by fourMerge branch '18.0-social-media-*' of … into 18.0commits in April 2026 that broke the fast-forward invariant. Every nightly sync since then quietly produced anotherMerge branch 'OCA:18.0' into 18.0merge commit on top, all flaggedsuccessby the workflow.What changes
fork_sync_digest.sync_branch()now takes an optionalupstream_organd, on a successful merge-upstream, calls/repos/{upstream}/{repo}/compare/{upstream}:{branch}...{fork}:{branch}to captureahead_by/behind_by. Setsdiverged = ahead_by > 0.upstream_orginforks.yml) skip the compare — one network call per fork, not per branch, only when meaningful.render_digest.render()adds async_divergedbucket: own warning section (⚠️ Diverged from upstream, amber not red), separate subject tag (⚠️ N diverged),exit_markerunchanged so divergence stays informational and doesn't conflate with "scripts broke".ahead_bystaysNoneand the branch is treated as not-known-diverged rather than falsely clean.Tests
6 new tests (25 total, all pass):
test_diverged_branch_is_flagged_when_upstream_org_provided— the 30-ahead social casetest_clean_fast_forward_is_not_divergedtest_no_upstream_org_skips_divergence_check— verifies only oneghcall happenstest_compare_failure_does_not_mask_successful_synctest_failed_sync_skips_comparetest_diverged_branch_warning_in_subject_and_body— render sideOut of scope
Auto-resetting diverged branches. The email surfaces the drift; manual
git refs PATCH … force=true(after backup) stays the recovery path, since reset-to-upstream is destructive and the workflow's PAT shouldn't have force-push authority on a series-named branch.