ci: draft PRs and skip reviews while the README notice is present

AI agents prepend a notice to README.md that the author removes once they
have reviewed the changes. Until that happens nobody else should look at
the PR: convert it to a draft, don't add the please-review label, and
don't start a Claude review. The labeler and the review workflow check
README.md at the PR head for the notice. Marking the PR ready for review
after removing the notice triggers the normal labeling again.

.github/workflows/claude-review.yml

@@ -63,6 +63,7 @@ jobs:
       pull-requests: write
 
     outputs:
+      skip: ${{ steps.context.outputs.skip }}
       pr_number: ${{ steps.context.outputs.pr_number }}
       comment_id: ${{ steps.context.outputs.comment_id }}
       head_sha: ${{ steps.context.outputs.head_sha }}
@@ -132,6 +133,21 @@ jobs:
               github.paginate(github.rest.pulls.listReviewComments, { owner, repo, pull_number: prNumber, per_page: 100 }),
             ]);
 
+            /* A README.md that still carries the AI review notice has not been
+             * looked at by its author yet, so there is nothing to review. */
+            const readme = await github.rest.repos.getContent({
+              owner,
+              repo,
+              path: "README.md",
+              ref: pr.data.head.sha,
+            });
+            if (Buffer.from(readme.data.content, "base64").toString()
+                .includes("Remove this line to confirm you've reviewed this PR before submitting.")) {
+              console.log("README.md still carries the review notice, skipping.");
+              core.setOutput("skip", "true");
+              return;
+            }
+
             /* Find or create tracking comment. */
             const existing = issueComments.find((c) =>
               c.user?.login === "github-actions[bot]" && c.body?.includes(MARKER));
@@ -201,6 +217,7 @@ jobs:
   review:
     runs-on: ubuntu-latest
     needs: setup
+    if: needs.setup.outputs.skip != 'true'
     timeout-minutes: 55
 
     permissions:
@@ -496,7 +513,7 @@ jobs:
     needs: [setup, review]
     # Run unless setup never started, so a setup that dies after creating the
     # tracking comment cannot strand the transient banner on the pull request.
-    if: always() && needs.setup.result != 'skipped'
+    if: always() && needs.setup.result != 'skipped' && needs.setup.outputs.skip != 'true'
 
     permissions:
       pull-requests: write

.github/workflows/labeler.yml

@@ -64,7 +64,28 @@ jobs:
             "good-to-merge/waiting-for-reporter-feedback 👍",
           ]);
 
-          if (Array.from(labels).filter(l => good_to_merge.has(l)).length == 0) {
+          /* A README.md that still carries the AI review notice has not been
+           * looked at by its author yet, so nobody else should review it. */
+          const readme = await github.rest.repos.getContent({
+            owner: context.repo.owner,
+            repo: context.repo.repo,
+            path: "README.md",
+            ref: context.payload.pull_request.head.sha,
+          });
+          const unreviewed = Buffer.from(readme.data.content, "base64").toString()
+            .includes("Remove this line to confirm you've reviewed this PR before submitting.");
+
+          if (unreviewed) {
+            /* Only GraphQL can do this. The author marks the PR ready again once
+             * the notice is gone, which triggers the labeling below. */
+            await github.graphql(`
+              mutation($id: ID!) {
+                convertPullRequestToDraft(input: { pullRequestId: $id }) {
+                  pullRequest { isDraft }
+                }
+              }
+            `, { id: context.payload.pull_request.node_id });
+          } else if (Array.from(labels).filter(l => good_to_merge.has(l)).length == 0) {
             labels.add("please-review");
           }