diff --git a/apps/web/src/browser/ElectronBrowserHost.browser.test.tsx b/apps/web/src/browser/ElectronBrowserHost.browser.test.tsx
index 5d1e02658d587..8df5bdbcb3d1c 100644
--- a/apps/web/src/browser/ElectronBrowserHost.browser.test.tsx
+++ b/apps/web/src/browser/ElectronBrowserHost.browser.test.tsx
@@ -5,8 +5,10 @@ import {
   ThreadId,
   type ClientSettings,
   type DesktopPreviewBridge,
+  type PreviewEvent,
   type PreviewSessionSnapshot,
 } from "@t3tools/contracts";
+import { AsyncResult, Atom } from "effect/reactivity";
 import { act } from "react";
 import { createRoot, type Root } from "react-dom/client";
 import { afterEach, beforeEach, describe, expect, it, vi } from "vite-plus/test";
@@ -20,6 +22,31 @@ const mocks = vi.hoisted(() => ({
   getPreviewConfig: vi.fn<DesktopPreviewBridge["getPreviewConfig"]>(),
 }));
 
+// Every preview event of the primary environment, for any thread.
+const primary = vi.hoisted(() => ({
+  environmentId: "host-primary",
+  events: null as unknown as Atom.Writable<AsyncResult.AsyncResult<PreviewEvent>>,
+}));
+
+vi.mock(import("~/state/primaryEnvironment"), async () => {
+  const { Atom } = await import("effect/reactivity");
+  return { primaryEnvironmentIdAtom: Atom.make(primary.environmentId as EnvironmentId) };
+});
+
+vi.mock(import("~/state/preview"), async (original) => {
+  const actual = await original();
+  const { AsyncResult, Atom } = await import("effect/reactivity");
+  primary.events = Atom.make<AsyncResult.AsyncResult<PreviewEvent>>(AsyncResult.initial());
+  return {
+    ...actual,
+    previewEnvironment: {
+      ...actual.previewEnvironment,
+      events: () => primary.events,
+      list: () => Atom.make(AsyncResult.initial()),
+    } as never,
+  };
+});
+
 vi.mock(import("~/env"), async (original) => ({ ...(await original()), isElectron: true }));
 
 vi.mock(import("~/state/session"), async (original) => ({
@@ -56,7 +83,7 @@ import {
   ensureClientSettingsHydrated,
 } from "~/hooks/useSettings";
 import { reconcilePreviewServerSessions, resetPreviewStateForTests } from "~/previewStateStore";
-import { AppAtomRegistryProvider } from "~/rpc/atomRegistry";
+import { AppAtomRegistryProvider, appAtomRegistry } from "~/rpc/atomRegistry";
 import { ElectronBrowserHost } from "./ElectronBrowserHost";
 
 const threadRef = scopeThreadRef(
@@ -160,4 +187,44 @@ describe("ElectronBrowserHost", () => {
     expect(after).toHaveLength(2);
     expect(after.every((node, index) => node.isSameNode(before[index]!))).toBe(true);
   });
+
+  it("hosts a server tab an agent opens in a thread the user is not viewing", async () => {
+    root = createRoot(container);
+    await act(async () => {
+      root!.render(
+        <AppAtomRegistryProvider>
+          <ElectronBrowserHost />
+        </AppAtomRegistryProvider>,
+      );
+      await ensureClientSettingsHydrated();
+    });
+
+    const backgroundThreadId = ThreadId.make("thread-agent-background");
+    await act(async () => {
+      appAtomRegistry.set(
+        primary.events,
+        AsyncResult.success({
+          type: "opened",
+          threadId: backgroundThreadId,
+          tabId: "tab_1",
+          createdAt: "2026-01-01T00:00:00.000Z",
+          serverEpoch: "server-a",
+          revision: 1,
+          snapshot: {
+            threadId: backgroundThreadId,
+            tabId: "tab_1",
+            runtime: "server",
+            automationOwner: "agent-session",
+            navStatus: { _tag: "Loading", url: "https://example.com/", title: "Example" },
+            canGoBack: false,
+            canGoForward: false,
+            updatedAt: "2026-01-01T00:00:00.000Z",
+          },
+        } as PreviewEvent),
+      );
+    });
+
+    const webviews = [...container.querySelectorAll("[data-electron-browser-host] webview")];
+    expect(webviews.map((node) => node.getAttribute("data-preview-server-tab"))).toEqual(["tab_1"]);
+  });
 });
diff --git a/apps/web/src/browser/ElectronBrowserHost.tsx b/apps/web/src/browser/ElectronBrowserHost.tsx
index 02e45bb950bef..8a94063e575ef 100644
--- a/apps/web/src/browser/ElectronBrowserHost.tsx
+++ b/apps/web/src/browser/ElectronBrowserHost.tsx
@@ -1,19 +1,28 @@
 "use client";
 
-import { parseScopedThreadKey } from "@t3tools/client-runtime/environment";
+import {
+  parseScopedThreadKey,
+  scopedThreadKey,
+  scopeThreadRef,
+} from "@t3tools/client-runtime/environment";
 import {
   AuthPreviewOperateScope,
   type DesktopPreviewOpenLinkEvent,
+  type EnvironmentId,
   FILL_PREVIEW_VIEWPORT,
+  type ScopedThreadRef,
+  ThreadId,
 } from "@t3tools/contracts";
 import { useAtomValue } from "@effect/atom-react";
+import { AsyncResult, Atom } from "effect/reactivity";
 import { type ComponentProps, useEffect, useEffectEvent, useState } from "react";
 
 import { primaryEnvironmentIdAtom } from "~/state/primaryEnvironment";
 
 import { isElectron } from "~/env";
 import { useClientSettingsHydrated } from "~/hooks/useSettings";
-import { useActivePreviewSessions } from "~/previewStateStore";
+import { usePreviewSession } from "~/components/preview/usePreviewSession";
+import { applyPreviewServerEvent, useActivePreviewSessions } from "~/previewStateStore";
 import { previewEnvironment } from "~/state/preview";
 import { useEnvironmentScope } from "~/state/session";
 import { useAtomCommand } from "~/state/use-atom-command";
@@ -26,9 +35,40 @@ import { openUrlInPreview } from "./openFileInPreview";
 import { rendersServerTabNatively } from "./previewRuntime";
 import { previewRuntimeTabId } from "./previewRuntimeTabId";
 
+/**
+ * The server binds a tab to this desktop's browser profile only if the desktop attaches it within
+ * seconds of opening; otherwise the tab runs in the server's own browser, without the user's
+ * sign-ins. Agents open tabs in threads the user is not viewing, so every server tab opened in the
+ * primary environment is seeded here instead of waiting for its thread's view to subscribe.
+ */
+const serverTabOpeningsAtom = Atom.family((environmentId: EnvironmentId) => {
+  const events = previewEnvironment.events({ environmentId, input: {} });
+  return Atom.make((get) => {
+    get.subscribe(events, (result) => {
+      if (!AsyncResult.isSuccess(result)) return;
+      const event = result.value;
+      if (event.type !== "opened" || event.snapshot.runtime !== "server") return;
+      applyPreviewServerEvent(scopeThreadRef(environmentId, ThreadId.make(event.threadId)), event);
+    });
+    get.mount(events);
+  });
+});
+
+const noServerTabOpeningsAtom = Atom.make(() => undefined);
+
 export function ElectronBrowserHost() {
   const previewByThreadKey = useActivePreviewSessions();
   const primaryEnvironmentId = useAtomValue(primaryEnvironmentIdAtom);
+  useAtomValue(
+    isElectron && primaryEnvironmentId !== null
+      ? serverTabOpeningsAtom(primaryEnvironmentId)
+      : noServerTabOpeningsAtom,
+  );
+  // A seeded tab's thread stays synced so its navigation and closing reach the webview below.
+  const syncedThreadRefs = Object.keys(previewByThreadKey).flatMap((threadKey) => {
+    const threadRef = parseScopedThreadKey(threadKey);
+    return threadRef?.environmentId === primaryEnvironmentId ? [threadRef] : [];
+  });
   const activeSessions = Object.entries(previewByThreadKey).flatMap(([threadKey, previewState]) => {
     const threadRef = parseScopedThreadKey(threadKey);
     return threadRef
@@ -116,6 +156,9 @@ export function ElectronBrowserHost() {
   if (!isElectron) return null;
   return (
     <div className="contents" data-electron-browser-host>
+      {syncedThreadRefs.map((threadRef) => (
+        <PreviewSessionSync key={scopedThreadKey(threadRef)} threadRef={threadRef} />
+      ))}
       {sessions.map(({ threadRef, snapshot, runtimeTabId, pictureInPicture, zoomFactor }) => {
         const url = snapshot.navStatus._tag === "Idle" ? null : snapshot.navStatus.url;
         return (
@@ -145,6 +188,11 @@ export function ElectronBrowserHost() {
   );
 }
 
+function PreviewSessionSync({ threadRef }: { readonly threadRef: ScopedThreadRef }) {
+  usePreviewSession(threadRef);
+  return null;
+}
+
 function AuthorizedBrowserWebview(props: ComponentProps<typeof HostedBrowserWebview>) {
   const canOperatePreview = useEnvironmentScope(
     props.threadRef.environmentId,