diff --git a/src/crates/core/src/service/config/types.rs b/src/crates/core/src/service/config/types.rs
index 8396c920f..c3341e8a5 100644
--- a/src/crates/core/src/service/config/types.rs
+++ b/src/crates/core/src/service/config/types.rs
@@ -92,7 +92,7 @@ impl ProjectConfig {
 
 /// App configuration.
 fn default_close_button_behavior() -> String {
-    "quit".to_string()
+    "minimize_to_tray".to_string()
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize)]
diff --git a/src/web-ui/src/app/layout/AppLayout.tsx b/src/web-ui/src/app/layout/AppLayout.tsx
index 154a89349..79910fa5e 100644
--- a/src/web-ui/src/app/layout/AppLayout.tsx
+++ b/src/web-ui/src/app/layout/AppLayout.tsx
@@ -421,11 +421,11 @@ const AppLayout: React.FC<AppLayoutProps> = ({ className = '' }) => {
           }
 
           // Windows / Linux: read the user's close-button preference.
-          let behavior: CloseBehavior = 'quit';
+          let behavior: CloseBehavior = 'minimize_to_tray';
           try {
-            behavior = (await configManager.getConfig<CloseBehavior>('app.close_button_behavior')) ?? 'quit';
+            behavior = (await configManager.getConfig<CloseBehavior>('app.close_button_behavior')) ?? 'minimize_to_tray';
           } catch {
-            // Fall back to quit if config cannot be read.
+            // Fall back to minimize_to_tray if config cannot be read.
           }
 
           try {
diff --git a/src/web-ui/src/infrastructure/config/components/BasicsConfig.tsx b/src/web-ui/src/infrastructure/config/components/BasicsConfig.tsx
index 35d4445f0..fd669f31e 100644
--- a/src/web-ui/src/infrastructure/config/components/BasicsConfig.tsx
+++ b/src/web-ui/src/infrastructure/config/components/BasicsConfig.tsx
@@ -597,10 +597,10 @@ function BasicsWindowBehaviorSection() {
       try {
         setLoading(true);
         const v = await configManager.getConfig<CloseBehavior>('app.close_button_behavior');
-        if (!cancelled) setBehavior(v ?? 'quit');
+        if (!cancelled) setBehavior(v ?? 'minimize_to_tray');
       } catch {
         // Key absent on first launch — fall back to default silently.
-        if (!cancelled) setBehavior('quit');
+        if (!cancelled) setBehavior('minimize_to_tray');
       } finally {
         if (!cancelled) setLoading(false);
       }