diff --git a/flake.nix b/flake.nix
index 588438c..14859ec 100644
--- a/flake.nix
+++ b/flake.nix
@@ -19,7 +19,7 @@
         inherit (pkgs.stdenv.hostPlatform) system;
       };
 
-      mkWebapp = { pkgs, brandDir ? ./branding/default, app ? "main" }:
+      mkWebapp = { pkgs, brandDir ? ./branding/default, app ? "main", extraEnv ? {} }:
         let
           buildScript = if app == "main" then "build" else "build:${app}";
           outDir = if app == "main" then "dist" else "dist-${app}";
@@ -59,13 +59,19 @@
           # pwa-assets.config.ts. brandDir is either ./branding/default
           # (a path inside this flake's source) or an external path that
           # nix has copied into the build sandbox.
+          #
+          # `extraEnv` flows in VITE_* and any other build-time env vars
+          # the caller wants to bake into the bundle (e.g. webapp-module
+          # passes VITE_NOSTR_RELAYS / VITE_LNBITS_BASE_URL / …; the
+          # server-deploy standalones module passes VITE_BASE_PATH +
+          # VITE_APP_NAME for per-app path mounts).
           env = {
             BRAND_DIR = "${brandDir}";
             BRAND_APP = if app == "main" then "" else app;
             # Avoid pnpm 10's interactive modules-purge prompt in the
             # sandbox (ERR_PNPM_ABORTED_REMOVE_MODULES_DIR_NO_TTY).
             CI = "true";
-          };
+          } // extraEnv;
 
           buildPhase = ''
             runHook preBuild