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🤖 Add splash screen for instant startup feedback (#226)
## Problem Users see dock icon but no window for 6-13s during app startup (varies by machine: ~6s on M3, ~13s on M1). Even with lazy-loaded services (#223), the renderer makes IPC calls on mount which requires services to be loaded first, so the main window can't appear until everything is ready. ## Solution Added native splash screen that appears instantly (<100ms) while services load. ## Implementation **Three-phase startup:** 1. **Show splash** - Native BrowserWindow with static HTML (<100ms) - No React, no IPC, no heavy dependencies - Matches app theme colors from colors.tsx - Shows "Loading services..." with spinner 2. **Load services** - Happens while splash is visible (~6-13s) - Config, IpcMain, AI SDK, tokenizer modules - User gets instant visual feedback 3. **Show main window** - Close splash, reveal app - Services guaranteed ready when window appears - Main window uses "ready-to-show" event to avoid white flash ## Changes - **Added `static/splash.html`** - Lightweight loading screen matching app theme - **Modified `src/main.ts`** - Three-phase startup with splash screen - **Updated `Makefile`** - Copy splash.html to dist during build ## Benefits - ✅ Instant visual feedback (<100ms vs 6-13s black screen) - ✅ No user confusion ("is it broken?") - ✅ Services guaranteed ready (no race conditions) - ✅ Clean transition to main window - ✅ All tests pass (410 tests) ## Testing Manually tested on M3 - splash appears instantly, main window appears ~6s later. _Generated with `cmux`_
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‎Makefile‎

Lines changed: 8 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -22,7 +22,7 @@
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include fmt.mk
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.PHONY: all build dev start clean help
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.PHONY: build-renderer version build-icons
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.PHONY: build-renderer version build-icons build-static
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.PHONY: lint lint-fix typecheck static-check
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.PHONY: test test-unit test-integration test-watch test-coverage test-e2e
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.PHONY: dist dist-mac dist-win dist-linux
@@ -58,11 +58,11 @@ dev: node_modules/.installed build-main ## Start development server (Vite + Type
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"bun x concurrently \"bun x tsc -w -p tsconfig.main.json\" \"bun x tsc-alias -w -p tsconfig.main.json\"" \
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"vite"
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start: node_modules/.installed build-main build-preload ## Build and start Electron app
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start: node_modules/.installed build-main build-preload build-static ## Build and start Electron app
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@bun x electron --remote-debugging-port=9222 .
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## Build targets (can run in parallel)
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build: node_modules/.installed src/version.ts build-renderer build-main build-preload build-icons ## Build all targets
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build: node_modules/.installed src/version.ts build-renderer build-main build-preload build-icons build-static ## Build all targets
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build-main: node_modules/.installed dist/main.js ## Build main process
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@@ -86,6 +86,11 @@ build-renderer: node_modules/.installed src/version.ts ## Build renderer process
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@echo "Building renderer..."
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@bun x vite build
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build-static: ## Copy static assets to dist
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@echo "Copying static assets..."
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@mkdir -p dist
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@cp static/splash.html dist/splash.html
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# Always regenerate version file (marked as .PHONY above)
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version: ## Generate version file
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@./scripts/generate-version.sh

‎src/main.ts‎

Lines changed: 132 additions & 25 deletions
Original file line numberDiff line numberDiff line change
@@ -126,6 +126,19 @@ if (!gotTheLock) {
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}
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let mainWindow: BrowserWindow | null = null;
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let splashWindow: BrowserWindow | null = null;
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/**
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* Format timestamp as HH:MM:SS.mmm for readable logging
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*/
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function timestamp(): string {
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const now = new Date();
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const hours = String(now.getHours()).padStart(2, "0");
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const minutes = String(now.getMinutes()).padStart(2, "0");
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const seconds = String(now.getSeconds()).padStart(2, "0");
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const ms = String(now.getMilliseconds()).padStart(3, "0");
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return `${hours}:${minutes}:${seconds}.${ms}`;
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}
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function createMenu() {
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const template: MenuItemConstructorOptions[] = [
@@ -182,28 +195,101 @@ function createMenu() {
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Menu.setApplicationMenu(menu);
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}
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async function createWindow() {
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// Lazy-load Config and IpcMain only when window is created
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// This defers loading heavy AI SDK dependencies until actually needed
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if (!config || !ipcMain || !loadTokenizerModulesFn) {
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/* eslint-disable no-restricted-syntax */
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// Dynamic imports are justified here for performance:
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// - IpcMain transitively imports the entire AI SDK (ai, @ai-sdk/anthropic, etc.)
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// - These are large modules that would block app startup if loaded statically
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// - Loading happens once on first window creation, then cached
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const [
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{ Config: ConfigClass },
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{ IpcMain: IpcMainClass },
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{ loadTokenizerModules: loadTokenizerFn },
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] = await Promise.all([
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import("./config"),
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import("./services/ipcMain"),
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import("./utils/main/tokenizer"),
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]);
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/* eslint-enable no-restricted-syntax */
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config = new ConfigClass();
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ipcMain = new IpcMainClass(config);
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loadTokenizerModulesFn = loadTokenizerFn;
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/**
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* Create and show splash screen - instant visual feedback (<100ms)
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*
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* Shows a lightweight native window with static HTML while services load.
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* No IPC, no React, no heavy dependencies - just immediate user feedback.
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*/
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async function showSplashScreen() {
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const startTime = Date.now();
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console.log(`[${timestamp()}] Showing splash screen...`);
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splashWindow = new BrowserWindow({
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width: 400,
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height: 300,
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frame: false,
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transparent: false,
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alwaysOnTop: true,
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center: true,
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resizable: false,
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show: false, // Don't show until HTML is loaded
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webPreferences: {
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nodeIntegration: false,
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contextIsolation: true,
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},
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});
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// Wait for splash HTML to load
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await splashWindow.loadFile(path.join(__dirname, "splash.html"));
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// Wait for the window to actually be shown and rendered before continuing
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// This ensures the splash is visible before we block the event loop with heavy work
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await new Promise<void>((resolve) => {
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splashWindow!.once("show", () => {
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const loadTime = Date.now() - startTime;
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console.log(`[${timestamp()}] Splash screen shown (${loadTime}ms)`);
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// Give one more event loop tick for the window to actually paint
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setImmediate(resolve);
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});
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splashWindow!.show();
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});
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splashWindow.on("closed", () => {
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console.log(`[${timestamp()}] Splash screen closed event`);
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splashWindow = null;
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});
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}
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/**
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* Close splash screen
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*/
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function closeSplashScreen() {
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if (splashWindow) {
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console.log(`[${timestamp()}] Closing splash screen...`);
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splashWindow.close();
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splashWindow = null;
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}
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}
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/**
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* Load backend services (Config, IpcMain, AI SDK, tokenizer)
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*
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* Heavy initialization (~6-13s) happens here while splash is visible.
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* This is the slow part that delays app startup.
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*/
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async function loadServices(): Promise<void> {
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if (config && ipcMain && loadTokenizerModulesFn) return; // Already loaded
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const startTime = Date.now();
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console.log(`[${timestamp()}] Loading services...`);
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/* eslint-disable no-restricted-syntax */
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// Dynamic imports are justified here for performance:
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// - IpcMain transitively imports the entire AI SDK (ai, @ai-sdk/anthropic, etc.)
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// - These are large modules (~6-13s load time) that would block splash from appearing
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// - Loading happens once, then cached
272+
const [
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{ Config: ConfigClass },
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{ IpcMain: IpcMainClass },
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{ loadTokenizerModules: loadTokenizerFn },
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] = await Promise.all([
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import("./config"),
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import("./services/ipcMain"),
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import("./utils/main/tokenizer"),
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]);
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/* eslint-enable no-restricted-syntax */
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config = new ConfigClass();
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ipcMain = new IpcMainClass(config);
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loadTokenizerModulesFn = loadTokenizerFn;
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const loadTime = Date.now() - startTime;
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console.log(`[${timestamp()}] Services loaded in ${loadTime}ms`);
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}
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function createWindow() {
291+
if (!ipcMain) {
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throw new Error("Services must be loaded before creating window");
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}
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209295
mainWindow = new BrowserWindow({
@@ -218,11 +304,19 @@ async function createWindow() {
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// Hide menu bar on Linux by default (like VS Code)
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// User can press Alt to toggle it
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autoHideMenuBar: process.platform === "linux",
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show: false, // Don't show until ready-to-show event
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});
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// Register IPC handlers with the main window
224311
ipcMain.register(electronIpcMain, mainWindow);
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// Show window once it's ready and close splash
314+
mainWindow.once("ready-to-show", () => {
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console.log(`[${timestamp()}] Main window ready to show`);
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mainWindow?.show();
317+
closeSplashScreen();
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});
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226320
// Open all external links in default browser
227321
mainWindow.webContents.setWindowOpenHandler(({ url }) => {
228322
void shell.openExternal(url);
@@ -278,14 +372,23 @@ if (gotTheLock) {
278372
}
279373

280374
createMenu();
281-
await createWindow();
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// Three-phase startup:
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// 1. Show splash immediately (<100ms) and wait for it to load
378+
// 2. Load services while splash visible (fast - ~100ms)
379+
// 3. Create window and start loading content (splash stays visible)
380+
// 4. When window ready-to-show: close splash, show main window
381+
await showSplashScreen(); // Wait for splash to actually load
382+
await loadServices();
383+
createWindow();
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// Note: splash closes in ready-to-show event handler
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// Start loading tokenizer modules in background after window is created
284387
// This ensures accurate token counts for first API calls (especially in e2e tests)
285388
// Loading happens asynchronously and won't block the UI
286389
if (loadTokenizerModulesFn) {
287390
void loadTokenizerModulesFn().then(() => {
288-
console.log("Tokenizer modules loaded");
391+
console.log(`[${timestamp()}] Tokenizer modules loaded`);
289392
});
290393
}
291394
// No need to auto-start workspaces anymore - they start on demand
@@ -301,7 +404,11 @@ if (gotTheLock) {
301404
// Only create window if app is ready and no window exists
302405
// This prevents "Cannot create BrowserWindow before app is ready" error
303406
if (app.isReady() && mainWindow === null) {
304-
void createWindow();
407+
void (async () => {
408+
await showSplashScreen();
409+
await loadServices();
410+
createWindow();
411+
})();
305412
}
306413
});
307414
}

‎static/splash.html‎

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<!DOCTYPE html>
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<html>
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<head>
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<meta charset="UTF-8">
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<meta name="viewport" content="width=device-width, initial-scale=1.0">
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<title>cmux - Loading</title>
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<style>
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* {
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margin: 0;
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padding: 0;
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box-sizing: border-box;
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}
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body {
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width: 400px;
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height: 300px;
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/* Match --color-background (hsl(0 0% 12%)) */
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background: hsl(0 0% 12%);
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display: flex;
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flex-direction: column;
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align-items: center;
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justify-content: center;
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font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
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/* Match --color-text (hsl(0 0% 83%)) */
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color: hsl(0 0% 83%);
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overflow: hidden;
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border-radius: 12px;
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box-shadow: 0 8px 32px rgba(0, 0, 0, 0.4);
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}
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.logo {
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font-size: 48px;
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font-weight: 700;
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letter-spacing: -2px;
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margin-bottom: 24px;
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/* Gradient from plan mode blue (hsl(210 70% 40%)) to exec mode purple (hsl(268.56deg 94.04% 55.19%)) */
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background: linear-gradient(135deg, hsl(210 70% 45%) 0%, hsl(268.56deg 94.04% 55.19%) 100%);
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-webkit-background-clip: text;
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-webkit-text-fill-color: transparent;
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background-clip: text;
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}
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.loading-text {
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font-size: 16px;
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/* Match --color-text-secondary (hsl(0 0% 42%)) */
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color: hsl(0 0% 42%);
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margin-bottom: 16px;
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}
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.spinner {
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width: 40px;
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height: 40px;
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/* Match --color-border (hsl(240 2% 25%)) */
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border: 3px solid hsl(240 2% 25%);
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/* Match --color-plan-mode (hsl(210 70% 40%)) */
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border-top-color: hsl(210 70% 40%);
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border-radius: 50%;
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animation: spin 0.8s linear infinite;
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}
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@keyframes spin {
62+
to { transform: rotate(360deg); }
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}
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.version {
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position: absolute;
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bottom: 20px;
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font-size: 11px;
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/* Match --color-text-secondary (hsl(0 0% 42%)) */
70+
color: hsl(0 0% 42%);
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}
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</style>
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</head>
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<body>
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<div class="logo">cmux</div>
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<div class="loading-text">Loading services...</div>
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<div class="spinner"></div>
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<div class="version">coder multiplexer</div>
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</body>
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</html>
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