fixes

modules/nixos/services/matrix/default.nix

@@ -91,14 +91,14 @@ let
             }
           ];
 
-          # Database configuration
+          # Database configuration — connect via Unix socket (peer auth via identMap)
           database = {
             name = "psycopg2";
             allow_unsafe_locale = true;
             args = {
               user = "synapse";
               database = "synapse";
-              host = "localhost";
+              host = "/run/postgresql";
               cp_min = 5;
               cp_max = 10;
             };