diff --git a/src/main.ts b/src/main.ts
index c67e540..8cf52dc 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -30,6 +30,12 @@ import { ConfigManager } from './ipc/config/manager';
 import { AppConfig } from './types/config';
 import { isAutoStartLaunch, syncAutoStart } from './utils/autoStart';
 import { safeStringifyPacket } from './utils/sensitiveDataMasking';
+import { IS_DEV_ENVIRONMENT } from './utils/paths';
+
+// Set app name early so Electron's userData path reflects the environment
+if (IS_DEV_ENVIRONMENT) {
+  app.setName('Gemini Nexus Dev');
+}
 
 const packetLogPath = path.join(app.getPath('userData'), 'orpc_packets.log');
 
@@ -63,7 +69,7 @@ if (squirrelStartup) {
   process.exit(0);
 }
 
-const inDevelopment = process.env.NODE_ENV === 'development';
+const inDevelopment = IS_DEV_ENVIRONMENT;
 const debugHttpProxy = process.env.http_proxy?.trim() || process.env.HTTP_PROXY?.trim();
 const debugHttpsProxy = process.env.https_proxy?.trim() || process.env.HTTPS_PROXY?.trim();
 const debugNoProxy = process.env.no_proxy?.trim() || process.env.NO_PROXY?.trim();
@@ -167,11 +173,7 @@ function showWindowsInstallNoticeIfNeeded() {
   });
 }
 
-const isDev = process.env.NODE_ENV === 'development' || !app.isPackaged;
-
-if (isDev) {
-  app.setName('Gemini Nexus Dev');
-}
+const isDev = IS_DEV_ENVIRONMENT;
 
 const gotSingleInstanceLock = app.requestSingleInstanceLock();
 
diff --git a/src/preload.ts b/src/preload.ts
index fbc32a1..d971d91 100644
--- a/src/preload.ts
+++ b/src/preload.ts
@@ -10,16 +10,15 @@ import os from 'os';
 let sentryEnabled = false;
 try {
   const home = os.homedir();
+  const isDev = process.env.NODE_ENV === 'development';
+  const appName = isDev ? 'Gemini Nexus Dev' : 'Gemini Nexus';
   let appDataPath = '';
   if (process.platform === 'win32') {
-    appDataPath = path.join(
-      process.env.APPDATA || path.join(home, 'AppData', 'Roaming'),
-      'Gemini Nexus',
-    );
+    appDataPath = path.join(process.env.APPDATA || path.join(home, 'AppData', 'Roaming'), appName);
   } else if (process.platform === 'darwin') {
-    appDataPath = path.join(home, 'Library', 'Application Support', 'Gemini Nexus');
+    appDataPath = path.join(home, 'Library', 'Application Support', appName);
   } else {
-    appDataPath = path.join(home, '.config', 'Gemini Nexus');
+    appDataPath = path.join(home, '.config', appName);
   }
 
   const configPath = path.join(appDataPath, 'gui_config.json');
diff --git a/src/server/main.ts b/src/server/main.ts
index af0ea2a..2ecfef6 100644
--- a/src/server/main.ts
+++ b/src/server/main.ts
@@ -9,11 +9,16 @@ import { ProxyConfig } from '../types/config';
 import { setServerConfig } from './server-config';
 import { registerApiLogging } from './logging/api-logging.plugin';
 
+import { IS_DEV_ENVIRONMENT } from '../utils/paths';
+
 let app: NestFastifyApplication | null = null;
 let currentPort: number = 0;
 
+/** Default port: 8046 in development, 8045 in production */
+const DEFAULT_PORT = IS_DEV_ENVIRONMENT ? 8046 : 8045;
+
 export async function bootstrapNestServer(config: ProxyConfig): Promise<boolean> {
-  const port = config.port || 8045;
+  const port = config.port || DEFAULT_PORT;
   if (app) {
     logger.info('NestJS server already running.');
     return true;
diff --git a/src/utils/paths.ts b/src/utils/paths.ts
index bcd0dd2..5c73067 100644
--- a/src/utils/paths.ts
+++ b/src/utils/paths.ts
@@ -3,6 +3,16 @@ import os from 'os';
 import fs from 'fs';
 import { execSync } from 'child_process';
 
+/**
+ * Detects whether the app is running in development mode.
+ * Uses NODE_ENV as the single source of truth. This is evaluated once
+ * at module load time so every consumer gets a consistent answer.
+ */
+export const IS_DEV_ENVIRONMENT = process.env.NODE_ENV === 'development';
+
+/** Directory name suffix applied in development to isolate from production data. */
+const DEV_SUFFIX = ' Dev';
+
 /**
  * Checks if the current platform is WSL.
  * @returns {boolean} True if the current platform is WSL, false otherwise.
@@ -75,29 +85,29 @@ function getWindowsUser(): string {
 
 export function getAppDataDir(): string {
   const home = os.homedir();
+  const appName = IS_DEV_ENVIRONMENT ? `Gemini Nexus${DEV_SUFFIX}` : 'Gemini Nexus';
 
   if (isWsl()) {
     const winUser = getWindowsUser();
-    return `/mnt/c/Users/${winUser}/AppData/Roaming/GeminiNexus`;
+    const wslName = IS_DEV_ENVIRONMENT ? 'GeminiNexusDev' : 'GeminiNexus';
+    return `/mnt/c/Users/${winUser}/AppData/Roaming/${wslName}`;
   }
 
   switch (process.platform) {
     case 'darwin':
-      return path.join(home, 'Library', 'Application Support', 'Gemini Nexus');
+      return path.join(home, 'Library', 'Application Support', appName);
     case 'win32':
-      return path.join(
-        process.env.APPDATA || path.join(home, 'AppData', 'Roaming'),
-        'Gemini Nexus',
-      );
+      return path.join(process.env.APPDATA || path.join(home, 'AppData', 'Roaming'), appName);
     case 'linux':
-      return path.join(home, '.config', 'Gemini Nexus');
+      return path.join(home, '.config', appName);
     default:
-      return path.join(home, '.geminiNexus');
+      return path.join(home, IS_DEV_ENVIRONMENT ? '.geminiNexusDev' : '.geminiNexus');
   }
 }
 
 export function getAgentDir(): string {
-  return path.join(os.homedir(), '.geminiNexus-agent');
+  const dirName = IS_DEV_ENVIRONMENT ? '.geminiNexus-agent-dev' : '.geminiNexus-agent';
+  return path.join(os.homedir(), dirName);
 }
 
 export function getAccountsFilePath(): string {