Fix Fork Pull Request Preview Discovery

.github/scripts/preview-github.mts

@@ -41,8 +41,9 @@ export function isCurrentPullRequest(
 }
 
 // Determine identity exclusively through GitHub's API, never through files
-// uploaded by PR code. workflow_run.pull_requests can be empty for fork PRs,
-// so resolve associated PRs through the commit API in that case as well.
+// uploaded by PR code. Both workflow_run.pull_requests and the commit's PR
+// associations can be empty for a fork, including a draft PR. Query current
+// open PR heads directly and require an exact repository and SHA match.
 export async function findPreview(
     github: GitHubClient,
     run: SourceRun,
@@ -63,10 +64,11 @@ export async function findPreview(
     if (workflow.path !== ".github/workflows/ci.yml") {
         return null;
     }
-    const prs = await github.paginate(
-        github.rest.repos.listPullRequestsAssociatedWithCommit,
-        { ...repo, commit_sha: run.head_sha, per_page: 100 },
-    );
+    const prs = await github.paginate(github.rest.pulls.list, {
+        ...repo,
+        state: "open",
+        per_page: 100,
+    });
     const candidates = prs.filter((pr) =>
         isCurrentPullRequest(pr, run.head_sha, repository),
     );

.github/scripts/preview-github.test.mts

@@ -27,6 +27,7 @@ const run: SourceRun = {
 const pr = {
     number: 42,
     state: "open",
+    draft: true,
     head: { sha },
     base: { repo: { full_name: "LiveSplit/LiveSplitOne" } },
 };
@@ -60,8 +61,12 @@ function githubFixture(
         let result: unknown;
         if (url.pathname.endsWith("/actions/workflows/1")) {
             result = { path: options.workflow ?? ".github/workflows/ci.yml" };
-        } else if (url.pathname.endsWith(`/commits/${sha}/pulls`)) {
+        } else if (url.pathname === `/repos/${repo.owner}/${repo.repo}/pulls`) {
             result = options.candidates ?? [pr];
+        } else if (url.pathname.endsWith(`/commits/${sha}/pulls`)) {
+            // GitHub returned no associations for the first live fork PR,
+            // despite its current head and uploaded artifact matching CI.
+            result = [];
         } else if (url.pathname.endsWith("/pulls/42")) {
             result = options.current ?? pr;
         } else if (url.pathname.endsWith("/actions/runs/9/artifacts")) {
@@ -106,14 +111,37 @@ function githubFixture(
     return { github: new Octokit({ request: { fetch: fetcher } }), calls };
 }
 
-test("discovers fork PRs through signed commit metadata without artifact-supplied identity", async () => {
+test("discovers a draft fork PR even when its commit has no PR associations", async () => {
     const { github, calls } = githubFixture();
     assert.deepEqual(await findPreview(github, run, repo), {
         number: 42,
         sha,
         artifact: 7,
     });
-    assert(calls.some((call) => call.path.endsWith(`/commits/${sha}/pulls`)));
+    assert(
+        calls.some(
+            (call) => call.path === `/repos/${repo.owner}/${repo.repo}/pulls`,
+        ),
+    );
+});
+
+test("ignores open PRs with a different head or base repository", async () => {
+    const { github } = githubFixture({
+        candidates: [
+            { ...pr, number: 43, head: { sha: "b".repeat(40) } },
+            {
+                ...pr,
+                number: 44,
+                base: { repo: { full_name: "other/repo" } },
+            },
+            pr,
+        ],
+    });
+    assert.deepEqual(await findPreview(github, run, repo), {
+        number: 42,
+        sha,
+        artifact: 7,
+    });
 });
 
 test("ignores runs from other repositories, failed CI, and non-PR events", async () => {