diff --git a/.github/workflows/canon-marker.yml b/.github/workflows/canon-marker.yml
index 39600d4..e23ab28 100644
--- a/.github/workflows/canon-marker.yml
+++ b/.github/workflows/canon-marker.yml
@@ -3,6 +3,10 @@ name: Canon marker
 on:
   pull_request:
 
+concurrency:
+  group: canon-marker-${{ github.ref }}
+  cancel-in-progress: true
+
 jobs:
   check:
     # The forge's runner carries the label `docker` (image node:22-bookworm);
diff --git a/.github/workflows/deploy-quartz.yml b/.github/workflows/deploy-quartz.yml
index 62f0c1c..cf7dbb6 100644
--- a/.github/workflows/deploy-quartz.yml
+++ b/.github/workflows/deploy-quartz.yml
@@ -17,6 +17,9 @@ concurrency:
 
 jobs:
   deploy:
+    # The shared workflow publishes through GitHub Pages actions, which fail on
+    # the forge's runner (capacity 1). Run it on the GitHub mirror only.
+    if: github.server_url == 'https://github.com'
     uses: GameCult/GameCult-Quartz/.github/workflows/quartz-pages.yml@main
     with:
       content-dir: Aetheria