diff --git a/.gitea/workflows/ui-test.yaml b/.gitea/workflows/ui-test.yaml
index fe40048..e78e722 100644
--- a/.gitea/workflows/ui-test.yaml
+++ b/.gitea/workflows/ui-test.yaml
@@ -16,14 +16,17 @@ on:
       - '.gitea/workflows/ui-test.yaml'
       - '!**/*.md'
 
-# Playwright launches its own `pnpm dev` on :5173. In host-mode the
-# runner shares the host's port namespace, so two parallel ui-test
-# jobs (e.g. a push event racing with a pull_request event for the
-# same commit) collide on EADDRINUSE. Group by the head commit so
-# push and pull_request events for the same sha share one bucket.
+# Playwright launches its own `pnpm dev` on :5173, and in host-mode
+# the runner shares the host's port namespace with every other job,
+# so two parallel ui-test runs collide on EADDRINUSE. Serialise via a
+# singleton concurrency group with queueing — new runs wait their
+# turn instead of cancelling the in-progress one. cancel-in-progress
+# is explicitly false because Gitea has shown spurious self-cancel
+# behaviour under cancel-in-progress: true even when no other run
+# shares the group.
 concurrency:
-  group: ui-test-${{ gitea.event.pull_request.head.sha || gitea.sha }}
-  cancel-in-progress: true
+  group: ui-test-singleton
+  cancel-in-progress: false
 
 jobs:
   test: