fix(ci): fetch author_association via REST API instead of webhook payload (#444)

The webhook payload field context.payload.pull_request.author_association
is unreliable under pull_request_target events — it was absent or not
populated, causing the previous fix (#442) to still fail.

Switch to fetching author_association via pulls.get REST API, which only
needs pull-requests permission (already granted) and reliably returns
MEMBER for org members regardless of membership visibility.

Also removes the redundant orgs.checkMembershipForUser and
repos.checkCollaborator fallbacks, which suffered from the same
GITHUB_TOKEN permission limitation that started this bug.

Co-authored-by: John Myers <[email protected]>

Author: johntmyers

.github/workflows/vouch-check.yml

@@ -19,56 +19,34 @@ jobs:
           script: |
             const author = context.payload.pull_request.user.login;
             const authorType = context.payload.pull_request.user.type;
-            const authorAssociation = context.payload.pull_request.author_association;
 
             // Skip bots (dependabot, renovate, github-actions, etc.).
             if (authorType === 'Bot') {
               console.log(`${author} is a bot. Skipping vouch check.`);
               return;
             }
 
-            // Check author_association from the webhook payload. This is set by
-            // GitHub itself and doesn't require extra token permissions, so it
-            // works reliably for org members even when their membership is private.
+            // Fetch author_association via the REST API. The webhook payload
+            // field (context.payload.pull_request.author_association) is
+            // unreliable under pull_request_target — it can be absent or stale.
+            // The pulls.get endpoint only needs pull-requests permission, which
+            // we already have, and reliably returns MEMBER for org members even
+            // when their membership is private.
             const trustedAssociations = ['MEMBER', 'OWNER', 'COLLABORATOR'];
-            if (trustedAssociations.includes(authorAssociation)) {
-              console.log(`${author} has author_association=${authorAssociation}. Skipping vouch check.`);
-              return;
-            }
-
-            // Fallback: explicit API checks in case author_association is unexpected.
-
-            // Check org membership — members bypass the vouch gate.
             try {
-              const { status } = await github.rest.orgs.checkMembershipForUser({
-                org: context.repo.owner,
-                username: author,
-              });
-              if (status === 204 || status === 302) {
-                console.log(`${author} is an org member (API). Skipping vouch check.`);
-                return;
-              }
-            } catch (e) {
-              if (e.status !== 404) {
-                console.log(`Org membership check error: ${e.message}`);
-              }
-            }
-
-            // Check collaborator status — direct collaborators bypass.
-            try {
-              const { status } = await github.rest.repos.checkCollaborator({
+              const { data: pr } = await github.rest.pulls.get({
                 owner: context.repo.owner,
                 repo: context.repo.repo,
-                username: author,
+                pull_number: context.payload.pull_request.number,
               });
-              if (status === 204) {
-                console.log(`${author} is a collaborator (API). Skipping vouch check.`);
+              const association = pr.author_association;
+              console.log(`${author}: author_association=${association}`);
+              if (trustedAssociations.includes(association)) {
+                console.log(`${author} has author_association=${association}. Skipping vouch check.`);
                 return;
               }
             } catch (e) {
-              if (e.status !== 404) {
-                console.log(`Collaborator check error: ${e.message}`);
-              }
+              console.log(`Failed to fetch PR author_association: ${e.message}`);
             }
 
             // Check the VOUCHED.td file on the dedicated "vouched" branch.