diff --git a/packages/web-ui/src/components/SandboxedIframe.ts b/packages/web-ui/src/components/SandboxedIframe.ts
index a6131858..fba7b7d8 100644
--- a/packages/web-ui/src/components/SandboxedIframe.ts
+++ b/packages/web-ui/src/components/SandboxedIframe.ts
@@ -559,14 +559,18 @@ ${runtimeFunctions.join("\n")}
 		}
 	}, true);
 
-	// Prevent window.location changes
-	const originalLocation = window.location;
-	Object.defineProperty(window, 'location', {
-		get: function() { return originalLocation; },
-		set: function(url) {
-			window.parent.postMessage({ type: 'open-external-url', url: url.toString() }, '*');
-		}
-	});
+	// Prevent window.location changes (only if not already redefined)
+	try {
+		const originalLocation = window.location;
+		Object.defineProperty(window, 'location', {
+			get: function() { return originalLocation; },
+			set: function(url) {
+				window.parent.postMessage({ type: 'open-external-url', url: url.toString() }, '*');
+			}
+		});
+	} catch (e) {
+		// Already defined, skip
+	}
 })();
 </script>`;
 	}
diff --git a/packages/web-ui/src/components/sandbox/ArtifactsRuntimeProvider.ts b/packages/web-ui/src/components/sandbox/ArtifactsRuntimeProvider.ts
index 5f2509f1..b0a7c3a5 100644
--- a/packages/web-ui/src/components/sandbox/ArtifactsRuntimeProvider.ts
+++ b/packages/web-ui/src/components/sandbox/ArtifactsRuntimeProvider.ts
@@ -43,7 +43,7 @@ export class ArtifactsRuntimeProvider implements SandboxRuntimeProvider {
 
 			(window as any).listArtifacts = async (): Promise<string[]> => {
 				// Online: ask extension
-				if ((window as any).__isExtensionContext?.()) {
+				if ((window as any).sendRuntimeMessage) {
 					const response = await (window as any).sendRuntimeMessage({
 						type: "artifact-operation",
 						action: "list",
@@ -61,7 +61,7 @@ export class ArtifactsRuntimeProvider implements SandboxRuntimeProvider {
 				let content: string;
 
 				// Online: ask extension
-				if ((window as any).__isExtensionContext?.()) {
+				if ((window as any).sendRuntimeMessage) {
 					const response = await (window as any).sendRuntimeMessage({
 						type: "artifact-operation",
 						action: "get",
@@ -94,7 +94,7 @@ export class ArtifactsRuntimeProvider implements SandboxRuntimeProvider {
 				content: any,
 				mimeType?: string,
 			): Promise<void> => {
-				if (!(window as any).__isExtensionContext?.()) {
+				if (!(window as any).sendRuntimeMessage) {
 					throw new Error("Cannot create/update artifacts in offline mode (read-only)");
 				}
 
@@ -117,7 +117,7 @@ export class ArtifactsRuntimeProvider implements SandboxRuntimeProvider {
 			};
 
 			(window as any).deleteArtifact = async (filename: string): Promise<void> => {
-				if (!(window as any).__isExtensionContext?.()) {
+				if (!(window as any).sendRuntimeMessage) {
 					throw new Error("Cannot delete artifacts in offline mode (read-only)");
 				}
 
diff --git a/packages/web-ui/src/components/sandbox/ConsoleRuntimeProvider.ts b/packages/web-ui/src/components/sandbox/ConsoleRuntimeProvider.ts
index d3b34eba..f5f4be5f 100644
--- a/packages/web-ui/src/components/sandbox/ConsoleRuntimeProvider.ts
+++ b/packages/web-ui/src/components/sandbox/ConsoleRuntimeProvider.ts
@@ -52,7 +52,7 @@ export class ConsoleRuntimeProvider implements SandboxRuntimeProvider {
 					(originalConsole as any)[method].apply(console, args);
 
 					// Send immediately and track the promise (only in extension context)
-					if ((window as any).__isExtensionContext?.()) {
+					if ((window as any).sendRuntimeMessage) {
 						const sendPromise = (window as any)
 							.sendRuntimeMessage({
 								type: "console",
@@ -108,7 +108,7 @@ export class ConsoleRuntimeProvider implements SandboxRuntimeProvider {
 
 				const finalError = error || lastError;
 
-				if ((window as any).__isExtensionContext?.()) {
+				if ((window as any).sendRuntimeMessage) {
 					if (finalError) {
 						await (window as any).sendRuntimeMessage({
 							type: "execution-error",
diff --git a/packages/web-ui/src/components/sandbox/FileDownloadRuntimeProvider.ts b/packages/web-ui/src/components/sandbox/FileDownloadRuntimeProvider.ts
index 313cc900..824ae125 100644
--- a/packages/web-ui/src/components/sandbox/FileDownloadRuntimeProvider.ts
+++ b/packages/web-ui/src/components/sandbox/FileDownloadRuntimeProvider.ts
@@ -53,7 +53,7 @@ export class FileDownloadRuntimeProvider implements SandboxRuntimeProvider {
 				}
 
 				// Send to extension if in extension context (online mode)
-				if ((window as any).__isExtensionContext?.()) {
+				if ((window as any).sendRuntimeMessage) {
 					const response = await (window as any).sendRuntimeMessage({
 						type: "file-returned",
 						fileName,
diff --git a/packages/web-ui/src/components/sandbox/RuntimeMessageBridge.ts b/packages/web-ui/src/components/sandbox/RuntimeMessageBridge.ts
index 1e838b15..b2e754e5 100644
--- a/packages/web-ui/src/components/sandbox/RuntimeMessageBridge.ts
+++ b/packages/web-ui/src/components/sandbox/RuntimeMessageBridge.ts
@@ -28,13 +28,6 @@ export class RuntimeMessageBridge {
 		// Returns stringified function that uses window.parent.postMessage
 		return `
 window.__completionCallbacks = [];
-// Check if we're in an extension context by examining the URL
-window.__isExtensionContext = () => {
-    const url = window.location.href;
-    return url.startsWith('chrome-extension://') ||
-           url.startsWith('moz-extension://') ||
-           url === 'about:srcdoc';
-};
 window.sendRuntimeMessage = async (message) => {
     const messageId = 'msg_' + Date.now() + '_' + Math.random().toString(36).substring(2, 9);
 
@@ -75,13 +68,6 @@ window.onCompleted = (callback) => {
 		// Returns stringified function that uses chrome.runtime.sendMessage
 		return `
 window.__completionCallbacks = [];
-// Check if we're in an extension context by examining the URL
-window.__isExtensionContext = () => {
-    const url = window.location.href;
-    return url.startsWith('chrome-extension://') ||
-           url.startsWith('moz-extension://') ||
-           url === 'about:srcdoc';
-};
 window.sendRuntimeMessage = async (message) => {
     return await chrome.runtime.sendMessage({
         ...message,