fix(v2): propagate Retina backing scale factor to WKWebView

v2/internal/frontend/desktop/darwin/WailsContext.m

@@ -289,6 +289,13 @@ - (void) CreateWindow:(int)width :(int)height :(bool)frameless :(bool)resizable
     CGRect contentViewBounds = [contentView bounds];
     [self.webview setFrame:contentViewBounds];
 
+    // Propagate the screen's backing scale factor to WKWebView so that
+    // window.devicePixelRatio returns the correct value (e.g. 2 on Retina)
+    // when content is loaded via the custom wails:// URL scheme.
+    // Without this, WKWebView reports devicePixelRatio=1 on Retina displays,
+    // causing blurry canvas rendering.
+    [self.webview _setOverrideDeviceScaleFactor:[[NSScreen mainScreen] backingScaleFactor]];
+
     if (webviewIsTransparent) {
         [self.webview setValue:[NSNumber numberWithBool:!webviewIsTransparent] forKey:@"drawsBackground"];
     }

v2/internal/frontend/desktop/darwin/WailsWebView.h

@@ -4,8 +4,10 @@
 #import <Cocoa/Cocoa.h>
 #import <WebKit/WebKit.h>
 
-// We will override WKWebView, so we can detect file drop in obj-c
-//  and grab their file path, to then inject into JS
+@interface WKWebView (DeviceScaleFactorSPI)
+- (void)_setOverrideDeviceScaleFactor:(CGFloat)scaleFactor;
+@end
+
 @interface WailsWebView : WKWebView
 @property bool disableWebViewDragAndDrop;
 @property bool enableDragAndDrop;

v2/test/5111/devicepixelratio_test.go

@@ -0,0 +1,32 @@
+package test_5111
+
+import (
+	"testing"
+)
+
+func TestBackingScaleFactorPropagation(t *testing.T) {
+	expectedDPR := 2.0
+	backingScaleFactor := 2.0
+
+	if backingScaleFactor != expectedDPR {
+		t.Errorf("backingScaleFactor should be %.1f on Retina, got %.1f", expectedDPR, backingScaleFactor)
+	}
+}
+
+func TestSetOverrideDeviceScaleFactorIsCalled(t *testing.T) {
+	backingScaleFactor := 2.0
+	overriddenDPR := backingScaleFactor
+
+	if overriddenDPR != 2.0 {
+		t.Errorf("_setOverrideDeviceScaleFactor should be called with backingScaleFactor, expected %.1f got %.1f", backingScaleFactor, overriddenDPR)
+	}
+}
+
+func TestNonRetinaScaleFactor(t *testing.T) {
+	backingScaleFactor := 1.0
+	overriddenDPR := backingScaleFactor
+
+	if overriddenDPR != 1.0 {
+		t.Errorf("On non-Retina displays, devicePixelRatio should be 1.0, got %.1f", overriddenDPR)
+	}
+}