~23% of reviews were failing open with `diff fetch failed: gitea GET
/{owner}/{repo}/compare/{before}...{after}.diff -> 404`. Probing the live
forge (Gitea 1.27.1) showed the web compare route answers 404 for ALL refs
on private repos — it does not honor `Authorization: token` and resolves as
anonymous — while the API compare (JSON) and per-commit
/git/commits/{sha}.diff endpoints succeed for the exact same sha pairs.
It also 404s legitimately when `before` is unknown (force-push, rebase).
fetchDiff now walks a fallback chain instead of failing open on the first
404 (any non-404 error still propagates immediately):
PR job: pulls/{n}.diff -> git/commits/{head}.diff
range push: web compare {before}...{after}.diff
-> web compare {defaultBranch}...{after}.diff
-> API compare commit list (falls back to the webhook's
commitShas) -> concatenated per-commit git/commits/{sha}.diff,
stopping past maxDiffBytes so the existing truncation cap
(verdict capped at 'warn') kicks in
-> git/commits/{after}.diff alone
new branch: git/commits/{after}.diff (unchanged)
Only when every source is exhausted does the review fail open, and the log
line now lists every URL tried. Webhook jobs carry the repo default_branch
so the fallback needs no extra API call; getRepo() covers recovered jobs
persisted before this change.
Verified against the live forge for the exact failing pair from today's
service.log (Nirlabinc/shreai 481d8663...46696b50): the chain recovers a
full-range 8,993-byte diff via 2/2 per-commit diffs.
Co-Authored-By: Claude Fable 5 <[email protected]>
Claude
a531323865