diff --git a/modules/nixos/substituters.nix b/modules/nixos/substituters.nix
--- a/modules/nixos/substituters.nix
+++ b/modules/nixos/substituters.nix
@@ -23,6 +23,12 @@ nix.settings = {
       substituters = caches;
       trusted-substituters = caches;
 
+      # A transient cache blip (e.g. cache.darksailor.dev briefly unreachable)
+      # should degrade to a local build, not abort the deploy. connect-timeout
+      # keeps a dead/flaky cache from stalling behind the long retry storm.
+      fallback = true;
+      connect-timeout = 5;
+
       trusted-public-keys = [
         "cache.darksailor.dev-1:SE3fTKFjzPJ6A5rrmZcRYlJme6/zSpRI1yVu3366u6k=" # harmonia (tako) cache signing key
         "cache.shiro-1:6LdQLhp0+TocABKct7ab9zqsUPTspiH7Y52N5qzPCvs=" # shiro cache signing key