diff --git a/apps/macos/Sources/Clawdis/CanvasWindow.swift b/apps/macos/Sources/Clawdis/CanvasWindow.swift
index 16ab0eda8..05630aa5c 100644
--- a/apps/macos/Sources/Clawdis/CanvasWindow.swift
+++ b/apps/macos/Sources/Clawdis/CanvasWindow.swift
@@ -311,11 +311,32 @@ final class CanvasWindowController: NSWindowController, WKNavigationDelegate, NS
             return
         }
         let scheme = url.scheme?.lowercased()
-        if scheme == CanvasScheme.scheme || scheme == "https" || scheme == "http" {
+
+        // Keep web content inside the panel when reasonable.
+        // `about:blank` and friends are common internal navigations for WKWebView; never send them to NSWorkspace.
+        if scheme == CanvasScheme.scheme
+            || scheme == "https"
+            || scheme == "http"
+            || scheme == "about"
+            || scheme == "blob"
+            || scheme == "data"
+            || scheme == "javascript"
+        {
             decisionHandler(.allow)
             return
         }
-        NSWorkspace.shared.open(url)
+
+        // Only open external URLs when there is a registered handler, otherwise macOS will show a confusing
+        // "There is no application set to open the URL ..." alert (e.g. for about:blank).
+        if let appURL = NSWorkspace.shared.urlForApplication(toOpen: url) {
+            NSWorkspace.shared.open(
+                [url],
+                withApplicationAt: appURL,
+                configuration: NSWorkspace.OpenConfiguration(),
+                completionHandler: nil)
+        } else {
+            canvasWindowLogger.debug("no application to open url \(url.absoluteString, privacy: .public)")
+        }
         decisionHandler(.cancel)
     }