diff --git a/.github/workflows/cd-staging.yml b/.github/workflows/cd-staging.yml
index ed59b70..c0ad3ea 100644
--- a/.github/workflows/cd-staging.yml
+++ b/.github/workflows/cd-staging.yml
@@ -252,6 +252,15 @@ jobs:
             echo "SENTRY_RELEASE=${{ github.event.pull_request.head.sha }}"
             echo "SENTRY_DSN_JOURNAL=$SENTRY_DSN_JOURNAL"
             echo "SENTRY_DSN_PLANNER=$SENTRY_DSN_PLANNER"
+            # Federation on previews too (social-federation rollout 12.4):
+            # makes any PR preview a second live trails instance that
+            # persistent staging can follow across — the trails-to-trails
+            # soak surface. FEDERATION_KEY_ENCRYPTION_KEY comes from the
+            # SOPS env decrypted above. Preview teardown orphans remote
+            # follower rows on the other side; remotes handle dead
+            # instances via ordinary delivery-failure expiry.
+            echo "FEDERATION_ENABLED=true"
+            echo "FEDERATION_LOG_LEVEL=debug"
           } >> infrastructure/staging-pr-${{ steps.ports.outputs.pr }}.env
 
       - name: Generate per-PR Caddyfile snippet
diff --git a/infrastructure/docker-compose.staging.yml b/infrastructure/docker-compose.staging.yml
index 0d4da27..1a09695 100644
--- a/infrastructure/docker-compose.staging.yml
+++ b/infrastructure/docker-compose.staging.yml
@@ -61,9 +61,9 @@ services:
       WAHOO_CLIENT_SECRET: ""
       WAHOO_WEBHOOK_TOKEN: ""
       DEMO_BOT_ENABLED: ""
-      # Federation soak (social-federation rollout step 12.2). Enabled by
-      # cd-staging.yml for persistent staging only; PR previews leave both
-      # empty (flag off) so preview journals never emit federation traffic.
+      # Federation (social-federation rollout). Enabled by cd-staging.yml
+      # for persistent staging (12.2) and for PR previews (12.4 — every
+      # preview is a second live instance staging can follow across).
       FEDERATION_ENABLED: ${FEDERATION_ENABLED:-}
       FEDERATION_KEY_ENCRYPTION_KEY: ${FEDERATION_KEY_ENCRYPTION_KEY:-}
       FEDERATION_LOG_LEVEL: ${FEDERATION_LOG_LEVEL:-}