fixup! fixup! fix nix develop psql setup

flake.nix

@@ -32,17 +32,21 @@
           ];
         };
 
-        postgresql = pkgs.postgresql_17;
+        # PostgreSQL 17 with PostGIS installed into PostgreSQL's
-        postgresqlPackages = postgresql.pkgs;
+        # extension path.
+        postgresql = pkgs.postgresql_17.withPackages (
+          ps: [
+            ps.postgis
+          ]
+        );
       in
       {
         devShells.default = pkgs.mkShell {
           packages = [
             rust
 
-            # PostgreSQL + matching PostGIS
+            # PostgreSQL + PostGIS
             postgresql
-            postgresqlPackages.postgis
 
             # SQLx migrations / CLI
             pkgs.sqlx-cli
@@ -61,7 +65,7 @@
             set -e
 
             # ============================================================
-            # Landkreis-Sprints development environment
+            # Environment
             # ============================================================
 
             export PGDATA="$PWD/.pgdata"
@@ -96,6 +100,9 @@
 
             # ============================================================
             # Start PostgreSQL
+            #
+            # No TCP listener. The development database is accessed
+            # exclusively through the Unix socket in .pgsocket.
             # ============================================================
 
             if ! pg_ctl \
@@ -209,18 +216,20 @@
             echo "  $(rustc --version)"
             echo
             echo "PostgreSQL:"
-            echo "  version:   $(psql --version)"
+            echo "  $(psql --version)"
-            echo "  host:      $PGHOST"
+            echo "  socket:    $PGHOST"
             echo "  database:  $PGDATABASE"
             echo "  user:      $PGUSER"
             echo
             echo "PostGIS:"
+
             psql \
               -h "$PGHOST" \
               -U "$PGUSER" \
               -d "$PGDATABASE" \
               -tAc "SELECT PostGIS_Full_Version();" |
               sed 's/^/  /'
+
             echo
             echo "DATABASE_URL:"
             echo "  $DATABASE_URL"