diff --git a/.gitea/workflows/ci.yaml b/.gitea/workflows/ci.yaml
index f0464f8..4fb965b 100644
--- a/.gitea/workflows/ci.yaml
+++ b/.gitea/workflows/ci.yaml
@@ -455,9 +455,16 @@ jobs:
         # week — recent enough that `--cache-from` still hits on normal traffic.
         #
         # Named volumes are never pruned here: that is where the trivy vuln DB lives.
+        #
+        # Both prunes carry an age filter, because "dangling" catches more than it looks.
+        # An image pulled by digest has no tag, so it is dangling the moment its container
+        # exits. A bare `docker image prune -f` therefore deleted the trivy image on every
+        # run and bought back a 157MB pull on the next one. The act runner image survived
+        # that only by accident: this step executes inside an act container, so the image
+        # is in use exactly while the prune runs. Relying on that is not a design.
         if: always()
         run: |
-          docker image prune -f
+          docker image prune -f --filter until=168h
           docker buildx prune -af --filter until=168h
           echo "--- dind disk after prune ---"
           docker system df