diff --git a/.github/workflows/playwright.yml b/.github/workflows/playwright.yml
index 24ee373..25756e7 100644
--- a/.github/workflows/playwright.yml
+++ b/.github/workflows/playwright.yml
@@ -113,11 +113,13 @@ jobs:
         run: test -n "$BOX_API_KEY"
       - name: Pick E2E ports for this runner
         # Several runners share one host. Each runner gets its own port set so the
-        # port-freeing steps and the harness never touch another job's servers.
+        # port-freeing steps and the harness never touch another job's servers. No runner
+        # uses the harness defaults: jobs from branches that still free the fixed ports
+        # cannot kill ours, and we cannot kill theirs.
         run: |
           set -euo pipefail
           suffix="${RUNNER_NAME##*-}"
-          offset=0
+          offset=100
           if [[ "$suffix" =~ ^[0-9]+$ ]]; then
             offset=$((suffix * 100))
           fi