diff --git a/apps/desktop/src/preview/Manager.test.ts b/apps/desktop/src/preview/Manager.test.ts
index 3bf6d63051af..d0bf5b91f258 100644
--- a/apps/desktop/src/preview/Manager.test.ts
+++ b/apps/desktop/src/preview/Manager.test.ts
@@ -58,6 +58,50 @@ describe("isPreviewRefreshShortcut", () => {
   });
 });
 
+describe("previewWindowOpenAction", () => {
+  const details = (overrides: {
+    readonly url?: string;
+    readonly disposition?: Electron.HandlerDetails["disposition"];
+  }) => ({
+    url: "https://accounts.google.com/o/oauth2/auth",
+    disposition: "new-window" as Electron.HandlerDetails["disposition"],
+    ...overrides,
+  });
+
+  it("opens a real window for scripted popups so the opener survives", () => {
+    // OAuth SDKs read a null `window.open()` as a blocked popup, and they need
+    // the opener alive to receive the credential back.
+    expect(PreviewManager.previewWindowOpenAction(details({}))).toBe("popup");
+    expect(
+      PreviewManager.previewWindowOpenAction(details({ url: "http://localhost:5173/auth" })),
+    ).toBe("popup");
+  });
+
+  it("keeps target=_blank links in the preview tab", () => {
+    expect(
+      PreviewManager.previewWindowOpenAction(details({ disposition: "foreground-tab" })),
+    ).toBe("navigate");
+    expect(
+      PreviewManager.previewWindowOpenAction(details({ disposition: "background-tab" })),
+    ).toBe("navigate");
+  });
+
+  it("does not hand a window to schemes that cannot be hardened", () => {
+    // A popup skips the `will-attach-webview` hardening, so it only gets a window
+    // when its preferences can be overridden. Chromium copies the guest's
+    // preferences for `about:blank` and forbids overriding them.
+    for (const url of [
+      "about:blank",
+      "javascript:alert(1)",
+      "file:///etc/passwd",
+      "vscode://vscode-remote/ssh-remote+box/tmp",
+      "not a url",
+    ]) {
+      expect(PreviewManager.previewWindowOpenAction(details({ url }))).toBe("navigate");
+    }
+  });
+});
+
 const {
   browserWindowConstructor,
   createFromPath,
diff --git a/apps/desktop/src/preview/Manager.ts b/apps/desktop/src/preview/Manager.ts
index 0d90e0175fe3..c1adbe7df774 100644
--- a/apps/desktop/src/preview/Manager.ts
+++ b/apps/desktop/src/preview/Manager.ts
@@ -434,6 +434,61 @@ const APP_FORWARDED_SHORTCUTS: ReadonlyArray<{
   { key: "w", meta: true, shift: false, control: false },
 ]);
 
+/**
+ * Protocols a preview page may open in a real popup window.
+ *
+ * `about:blank` stays out: Chromium skips browser-side navigation for it, so the
+ * child copies the guest's `contextIsolation: false` preferences and Electron
+ * gives no way to override them. Those popups keep loading in the preview tab.
+ *
+ * Deliberately not `ElectronShell.parseSafeExternalUrl`: that also admits
+ * `vscode://vscode-remote/...` deep links, which belong in `shell.openExternal`
+ * and not in a window spawned by a third-party page in the preview.
+ */
+const POPUP_PROTOCOLS = new Set(["http:", "https:"]);
+
+const isPopupUrl = (rawUrl: string): boolean => {
+  try {
+    return POPUP_PROTOCOLS.has(new URL(rawUrl).protocol);
+  } catch {
+    return false;
+  }
+};
+
+/**
+ * Preferences for a popup a preview page opens.
+ *
+ * A popup is not a webview attach, so the `will-attach-webview` hardening in
+ * `DesktopWindow` never sees it, and an unoverridden child would inherit the
+ * guest's relaxed posture: the picker preload needs `contextIsolation: false`
+ * to share `globalThis` with the previewed page, and no OAuth provider should
+ * get that. The window keeps the opener and the guest session either way.
+ */
+const POPUP_WINDOW_OPTIONS = {
+  webPreferences: {
+    contextIsolation: true,
+    nodeIntegration: false,
+    sandbox: true,
+  },
+} satisfies Electron.BrowserWindowConstructorOptions;
+
+/**
+ * Decides what a preview page's `window.open` should do.
+ *
+ * `"popup"` opens a real window, which scripted popups need: denying them makes
+ * `window.open()` return `null` (OAuth SDKs report that as a blocked popup), and
+ * navigating the preview tab instead destroys the opener the popup has to
+ * `postMessage` its result back to.
+ *
+ * `target="_blank"` links arrive as a tab disposition and keep loading in the
+ * preview tab, which is what people expect from a link inside a preview.
+ */
+export const previewWindowOpenAction = (details: {
+  readonly url: string;
+  readonly disposition: Electron.HandlerDetails["disposition"];
+}): "popup" | "navigate" =>
+  details.disposition === "new-window" && isPopupUrl(details.url) ? "popup" : "navigate";
+
 export const isPreviewRefreshShortcut = (input: Electron.Input): boolean =>
   input.type === "keyDown" &&
   input.key.toLowerCase() === "r" &&
@@ -1661,6 +1716,12 @@ const makeNativeOperations = Effect.fn("PreviewManager.makeOperations")(function
         ],
       });
     });
+    // A popup opens with Electron's default handler, so the page inside it could
+    // otherwise spawn native windows without limit. Nothing in an OAuth flow
+    // opens a second popup, so the chain stops at the first one.
+    const windowCreated = (window: Electron.BrowserWindow): void => {
+      window.webContents.setWindowOpenHandler(() => ({ action: "deny" }));
+    };
     const beforeInput = (event: Electron.Event, input: Electron.Input): void => {
       if (isPreviewRefreshShortcut(input)) {
         event.preventDefault();
@@ -1686,6 +1747,7 @@ const makeNativeOperations = Effect.fn("PreviewManager.makeOperations")(function
         wc.off("did-stop-loading", sync);
         wc.off("did-fail-load", failed as never);
         wc.off("audio-state-changed", audioStateChanged);
+        wc.off("did-create-window", windowCreated);
         wc.off("before-input-event", beforeInput);
         wc.ipc.off(HUMAN_INPUT_CHANNEL, humanInput);
         wc.ipc.off(MOUSE_NAVIGATE_CHANNEL, mouseNavigate);
@@ -1704,14 +1766,18 @@ const makeNativeOperations = Effect.fn("PreviewManager.makeOperations")(function
         wc.on("audio-state-changed", audioStateChanged);
         wc.ipc.on(HUMAN_INPUT_CHANNEL, humanInput);
         wc.ipc.on(MOUSE_NAVIGATE_CHANNEL, mouseNavigate);
-        wc.setWindowOpenHandler(({ url }) => {
+        wc.setWindowOpenHandler((details) => {
+          if (previewWindowOpenAction(details) === "popup") {
+            return { action: "allow", overrideBrowserWindowOptions: POPUP_WINDOW_OPTIONS };
+          }
           runFork(
             attemptPromise({ operation: "openPreviewWindow", tabId, webContentsId: wc.id }, () =>
-              wc.loadURL(url),
+              wc.loadURL(details.url),
             ).pipe(Effect.ignore),
           );
           return { action: "deny" };
         });
+        wc.on("did-create-window", windowCreated);
         wc.on("before-input-event", beforeInput);
       });
       yield* Ref.update(attachedRef, (attached) =>
diff --git a/apps/web/src/browser/HostedBrowserWebview.tsx b/apps/web/src/browser/HostedBrowserWebview.tsx
index ae0526abb15f..6b85ebc829ee 100644
--- a/apps/web/src/browser/HostedBrowserWebview.tsx
+++ b/apps/web/src/browser/HostedBrowserWebview.tsx
@@ -92,7 +92,6 @@ export function HostedBrowserWebview(props: {
 
   const setWebviewRef = useCallback((node: HTMLElement | null) => {
     webviewRef.current = node as ElectronWebview | null;
-    if (node && !node.hasAttribute("allowpopups")) node.setAttribute("allowpopups", "true");
   }, []);
 
   useEffect(() => {
@@ -259,6 +258,10 @@ export function HostedBrowserWebview(props: {
         <webview
           key={webviewGeneration}
           ref={setWebviewRef}
+          // Must be an attribute on the element itself: Electron reads it when the
+          // guest attaches, so setting it from the ref callback lands too late and
+          // the guest attaches with popups disabled.
+          allowpopups="true"
           src={webviewGeneration === 0 ? initialSrc : recoverySrc}
           partition={config.partition}
           webpreferences={config.webPreferences}