2026-07-27 18:33:24 +02:00
1 changed files with 16 additions and 6 deletions
@@ -74,13 +74,24 @@ in each caller:
  none) or a local diff, not a tighter check here; the guarantee is stated narrowly rather than left
  to read as complete.

-**Base-ref checkout — now a property of the tree.** `review-verdict.yml` checks out the PR's BASE
-ref (`ref: ${{ github.event.pull_request.base.sha }}`, `persist-credentials: false`), never the
-head, so the workflow that judges a PR cannot be rewritten by that same PR to weaken its own
-judgment. The checkout and its `ref` are the security-relevant parts — a bare `run:` calling the
+**Base-ref checkout — binds the SCRIPTS to the base, not the workflow itself.** `review-verdict.yml`
+checks out the PR's BASE ref (`ref: ${{ github.event.pull_request.base.sha }}`,
+`persist-credentials: false`), never the head, so the *scripts the job executes* — above all
+`scripts/pr-changed-files.sh` — come from the already-reviewed base rather than from the PR under
+judgment. The checkout and its `ref` are the security-relevant parts: a bare `run:` calling the
 script would not have been sufficient, since the script would then have come from wherever the
 runner happened to be.

+**It does NOT mean a PR cannot rewrite the gate that judges it (#672).** Gitea resolves a
+`pull_request` workflow *definition* from the PR's own head, so a PR editing `review-verdict.yml`
+runs its own rewritten copy — which can delete this checkout, or simply post
+`review-verdict/h10=success` for its head sha and stop. Branch protection does not close that: it
+requires the *context*, not an author, and carries `required_approvals: 0`. An earlier revision of
+this paragraph said the workflow "cannot be rewritten by that same PR to weaken its own judgment",
+which is true of the scripts and false of the workflow — and stated in the one sentence a reader
+resolving this record from the catalog is most likely to stop at. Contained today only by push
+access being required; tracked in #672.
+
 An earlier revision of this record stated the requirement in the future tense, because the wiring
 was staged over two PRs: the workflow runs the BASE version of the gate, and until the shared script
 existed on `main` a wired workflow would have exited 127 on its own PR and blocked the merge gate
@@ -89,8 +100,7 @@ through the combined status. That staging is complete. Both halves are asserted
 matching it — `head.sha` for `base.sha` is a nine-character diff, and a text-level check would still
 pass if a second checkout step took the head afterwards and won.

-**What is deliberately NOT claimed.** The base-ref checkout closes the self-rewrite route through
-the *scripts*; it does not make the workflow immune to everything a PR controls. The `PROTECTED`
+**What is deliberately NOT claimed.** Beyond the head-resolution hole above, the `PROTECTED`
 path list remains the guard that stops a bot-authored PR from editing the gate and exempting itself,
 and mutation testing was what established that `PROTECTED` is load-bearing only on the BOT path —
 it and `DOCS_ONLY` are disjoint patterns, so on the docs-only path that clause can never fire. A