diff --git a/app.js b/app.js
index 54b8d3f4..0bcf5072 100644
--- a/app.js
+++ b/app.js
@@ -37,6 +37,7 @@ let util;
 let dir;
 let log;
 let pre;
+let alt;
 
 const EventEmitter = require('events');
 class AppEmitter extends EventEmitter {}
@@ -64,6 +65,7 @@ function init(mod) {
     startTime = time();
     lastmod = mod.util.lastmod;
     logger = mod.log;
+    alt = ENV.alt;
     pre = ENV.pre || mod.meta.pre;
     debug = ENV.debug || mod.meta.debug;
     oversion = ENV.over || mod.meta.over;
@@ -191,6 +193,14 @@ function init(mod) {
             append[key] = minify(append[key]);
         }
     }
+
+    if (alt) {
+        for (let [ key, val ] of Object.entries(append)) {
+            fs.mkdirSync(`alt/main`, { recursive: true });
+            let body = fs.readFileSync(`src/main/${key}.js`);
+            fs.writeFileSync(`alt/main/${key}.js`, body + val);
+        }
+    }
 };
 
 // either add module assets to path or require(init.js)
@@ -288,14 +298,14 @@ function initModule(mod, file, dir) {
             const path = mod.dir + '/' + dir + '/' + file;
             try {
                 const body = fs.readFileSync(path);
-                // console.log({ inject: code, file, opt });
+                logger.log({ inject: code, file, opt });
                 if (opt.first) {
                     append[code] = body.toString() + '\n' + append[code];
                 } else {
                     append[code] += body.toString() + '\n';
                 }
             } catch (e) {
-                console.log({ missing_file: path, dir, mod });
+                logger.log({ missing_file: path, dir, mod });
             }
         },
         onload(fn) {
@@ -430,6 +440,10 @@ function generateDevices() {
     let dstr = JSON.stringify(devs);
     util.mkdir(PATH.join(dir,"src","pack"));
     fs.writeFileSync(PATH.join(dir,"src","pack","kiri-devs.js"), `export const devices = ${dstr};`);
+    if (alt) {
+        fs.mkdirSync('alt/pack', { recursive: true });
+        fs.writeFileSync(PATH.join(dir,"alt","pack","kiri-devs.js"), `export const devices = ${dstr};`);
+    }
 }
 
 function minify(code) {
diff --git a/bin/bundle.config.json b/bin/bundle.config.json
index 93994e27..e7bd3566 100644
--- a/bin/bundle.config.json
+++ b/bin/bundle.config.json
@@ -5,7 +5,8 @@
     },
     "inputs": [
       { "root": "web", "prefix": "" },
-      { "root": "src", "prefix": "lib" },
+      { "root": "alt", "prefix": "lib"},
+      { "root": "src", "prefix": "lib"},
       { "root": "src/wasm", "prefix": "wasm" },
       { "root": "src/wasm", "prefix": "lib/kiri/wasm" }
     ],
diff --git a/bin/bundler.mjs b/bin/bundler.mjs
index 3a96efb4..36d66e9e 100644
--- a/bin/bundler.mjs
+++ b/bin/bundler.mjs
@@ -32,13 +32,19 @@ function* walk(dir, seen = new Set()) {
 
 // --- collect all files according to config ---
 let entries = [];
+let virtMap = new Set();
 for (const input of inputs) {
     const root = input.root;
     const prefix = input.prefix || '';
     for (const file of walk(root)) {
         const rel = path.relative(root, file).replace(/\\/g, '/');
         const virt = prefix ? `${prefix}/${rel}` : rel;
-        entries.push({ file, virt });
+        if (virtMap.has(virt)) {
+            console.log('pre-existing', virt, rel, root);
+        } else {
+            entries.push({ file, virt });
+            virtMap.add(virt);
+        }
     }
 }