diff --git a/nix/modules/hive-c0re.nix b/nix/modules/hive-c0re.nix
index 67995565..22171979 100644
--- a/nix/modules/hive-c0re.nix
+++ b/nix/modules/hive-c0re.nix
@@ -307,9 +307,21 @@ in
         HYPERHIVE_SWARM_NAME = config.services.hyperhive.swarmName;
       }
       // lib.optionalAttrs config.services.hyperhive.forge.enable {
-        # Agents poll this URL for Forgejo notifications. Derived from
-        # services.hyperhive.forge.{domain,httpPort} so it tracks forge config changes.
-        HIVE_FORGE_URL = "http://${config.services.hyperhive.forge.domain}:${toString config.services.hyperhive.forge.httpPort}";
+        # Agents poll this URL for Forgejo notifications + run all
+        # `hive-forge` calls against it. Pinned to `127.0.0.1` for
+        # the in-cluster path: every agent container shares the
+        # host's network namespace so loopback reaches the forge
+        # container directly, no DNS lookup needed (closes #761).
+        #
+        # Post-#754 `cfg.domain` defaults to `forge.<hive-domain>`
+        # for the external gateway vhost. Using that value here
+        # would route every in-cluster call through DNS for an
+        # external hostname agents can't resolve from inside their
+        # nspawn — every `hive-forge` invocation would fail with
+        # "Name or service not known". The external gateway URL
+        # is for operator browsers + cross-host clients; internal
+        # callers stay on loopback.
+        HIVE_FORGE_URL = "http://127.0.0.1:${toString config.services.hyperhive.forge.httpPort}";
       }
       // lib.optionalAttrs config.services.hyperhive.matrix.gui.enable {
         # Availability flag for `/api/state.matrix_gui_enabled`. The