fix(companion): drop stale has-companion label + document schedule caveat

Mirror of copilot: clear() removes the has-companion label when a PR's companions
are all removed; schedule default-branch caveat documented; github-script kept at
@v7 to match repo convention.

Author: Sg312

.github/workflows/companion-pr-check.yml

@@ -17,8 +17,11 @@ on:
     types: [opened, edited, reopened, synchronize]
     branches: [staging, main]
   schedule:
-    # Refresh open staging/main PRs in case the companion merges AFTER this PR
-    # was opened (scheduled runs use the workflow from the default branch).
+    # Refresh open staging/main PRs in case the companion merges AFTER this PR was
+    # opened. CAVEAT: GitHub runs scheduled workflows ONLY from the DEFAULT branch's
+    # copy of this file — so this auto-refresh activates once the workflow lands on
+    # the default branch (via the normal promotion), not before. The pull_request
+    # triggers below always work; re-editing the PR re-runs the check meanwhile.
     - cron: '*/30 * * * *'
   workflow_dispatch: {}
 
@@ -104,6 +107,9 @@ jobs:
             async function clear(prNumber) {
               const ex = await findSticky(prNumber);
               if (ex) await github.rest.issues.deleteComment({ owner, repo, comment_id: ex.id });
+              // Drop the label too, so a PR edited to remove all companions doesn't
+              // keep a stale has-companion badge. 404 if not present → ignore.
+              try { await github.rest.issues.removeLabel({ owner, repo, issue_number: prNumber, name: 'has-companion' }); } catch {}
             }
             async function ensureLabel() {
               try { await github.rest.issues.getLabel({ owner, repo, name: 'has-companion' }); }