diff --git a/nix/modules/swarm.nix b/nix/modules/swarm.nix
index d36e676..755ca6f 100644
--- a/nix/modules/swarm.nix
+++ b/nix/modules/swarm.nix
@@ -5,11 +5,17 @@
 {
   virtualisation.docker = {
     enable = true;
-    # Reclaim disk from churning per-run images/volumes (cc-ci root is ~28 GiB).
+    # Reclaim disk from churning per-run images (cc-ci root is ~28 GiB). Prune images/containers/
+    # networks/build-cache older than 24h — but NEVER volumes:
+    #  (1) `--volumes` is incompatible with `--filter until=` (docker errors → the unit failed daily,
+    #      degrading the system and never actually pruning — that's why disk crept to 96%); and
+    #  (2) Phase 2w keeps DATA-WARM canonical volumes that are UNDEPLOYED (no container), so
+    #      `prune --volumes` would DELETE the warm known-good data. Warm volumes are pruned
+    #      deliberately by the warm reconcilers (WC8), never by this blanket sweep.
     autoPrune = {
       enable = true;
       dates = "daily";
-      flags = [ "--all" "--volumes" "--filter" "until=24h" ];
+      flags = [ "--all" "--filter" "until=24h" ];
     };
   };