refactor(preview): the server always owns the browser engine

Desktop-managed servers left browser tabs to Electron, behind
T3CODE_SERVER_BROWSER, so agents, remote clients, and fixes split across
two engines. The server browser now always runs and every environment
offers server tabs.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

Author: juliusmarminge

apps/server/src/environment/ServerEnvironment.ts

@@ -20,7 +20,6 @@ import { readAgentActivityPublishingActive } from "../cloud/config.ts";
 import { resolveServerSelfUpdateCapability } from "../cloud/selfUpdate.ts";
 import { resolveServiceLauncherMode } from "../cloud/serviceLauncherClient.ts";
 import * as ServerConfig from "../config.ts";
-import { isServerBrowserEnabled } from "../preview/serverBrowserEnabled.ts";
 import * as ProcessRunner from "../processRunner.ts";
 import { resolveServerEnvironmentLabel } from "./ServerEnvironmentLabel.ts";
 import { detectServerEnvironmentMachineKind } from "./ServerEnvironmentMachine.ts";
@@ -258,7 +257,7 @@ export const make = Effect.gen(function* () {
         ? { serverSelfUpdateProgress: true }
         : {}),
       ...(desktopAppUpdate ? { desktopAppUpdate: true } : {}),
-      ...(isServerBrowserEnabled(serverConfig.mode) ? { serverBrowser: true } : {}),
+      serverBrowser: true,
     },
   };
 

apps/server/src/preview/Manager.ts

@@ -39,9 +39,7 @@ import * as PubSub from "effect/PubSub";
 import * as Scope from "effect/Scope";
 import * as Stream from "effect/Stream";
 import * as SynchronizedRef from "effect/SynchronizedRef";
-import * as ServerConfig from "../config.ts";
 import { PreviewControlRequiredError } from "@t3tools/contracts";
-import { isServerBrowserEnabled } from "./serverBrowserEnabled.ts";
 
 export class PreviewManager extends Context.Service<
   PreviewManager,
@@ -132,8 +130,6 @@ const currentIsoTimestamp = DateTime.now.pipe(Effect.map(DateTime.formatIso));
 
 /** @public Service construction is part of the canonical Effect module API. */
 export const make = Effect.gen(function* PreviewManagerMake() {
-  const config = yield* ServerConfig.ServerConfig;
-  const serverBrowser = isServerBrowserEnabled(config.mode);
   const serverEpoch = NodeCrypto.randomUUID();
   const stateRef = yield* SynchronizedRef.make<ManagerState>(initialState);
   // Unbounded PubSub is fine here — events are tiny and we don't want to
@@ -200,8 +196,7 @@ export const make = Effect.gen(function* PreviewManagerMake() {
 
   const open: PreviewManager["Service"]["open"] = Effect.fn("PreviewManager.open")(
     function* (input) {
-      // Without a server browser nothing renders server tabs, so the client renders it.
-      const runtime = input.runtime === "server" && !serverBrowser ? undefined : input.runtime;
+      const runtime = input.runtime;
       // Persisted client surfaces must not bind to a different tab after a server restart.
       const tabId = `${newPreviewTabId()}${runtime === "server" ? `_${serverEpoch}` : ""}`;
       const updatedAt = yield* currentIsoTimestamp;

apps/server/src/preview/ServerBrowser.test.ts

@@ -18,7 +18,7 @@ import * as Layer from "effect/Layer";
 import * as Option from "effect/Option";
 import * as Queue from "effect/Queue";
 import type { BrowserContext, Page } from "playwright-core";
-import { afterEach, beforeEach, expect, vi } from "vite-plus/test";
+import { beforeEach, expect, vi } from "vite-plus/test";
 
 import * as ServerConfig from "../config.ts";
 import * as ServerEnvironment from "../environment/ServerEnvironment.ts";
@@ -188,9 +188,7 @@ beforeEach(() => {
   contexts.length = 0;
   contextGate = null;
   contextFailure = null;
-  vi.stubEnv("T3CODE_SERVER_BROWSER", "1");
 });
-afterEach(() => vi.unstubAllEnvs());
 
 it.live("readiness none responds immediately but takeover input waits for navigation commit", () =>
   Effect.scoped(

apps/server/src/preview/ServerBrowser.ts

@@ -67,7 +67,6 @@ import * as ServerBrowserPage from "./ServerBrowserPage.ts";
 import * as ServerBrowserToolchain from "./ServerBrowserToolchain.ts";
 import { ServerBrowserContexts } from "./ServerBrowserContexts.ts";
 import { BrowserControlInterrupted, SessionControl } from "./SessionControl.ts";
-import { isServerBrowserEnabled } from "./serverBrowserEnabled.ts";
 
 const SERVER_HOST_CLIENT_ID = "server-browser";
 const RENDER_SCALE = 2;
@@ -186,7 +185,6 @@ export interface ServerBrowserViewer {
 export class ServerBrowser extends Context.Service<
   ServerBrowser,
   {
-    readonly enabled: boolean;
     readonly attachViewer: (input: {
       readonly threadId: string;
       readonly tabId: string;
@@ -407,7 +405,6 @@ const CLIPBOARD_SCRIPT = `(() => {
 
 const make = Effect.gen(function* () {
   const config = yield* ServerConfig.ServerConfig;
-  const enabled = isServerBrowserEnabled(config.mode);
   const manager = yield* PreviewManager.PreviewManager;
   const broker = yield* PreviewAutomationBroker.PreviewAutomationBroker;
   const environment = yield* ServerEnvironment.ServerEnvironment;
@@ -1935,51 +1932,49 @@ const make = Effect.gen(function* () {
       } satisfies ServerBrowserViewer;
     });
 
-  if (enabled) {
-    yield* manager.events.pipe(Stream.runForEach(mirrorManagerEvent), Effect.forkScoped);
-    yield* Effect.sync(closeIdleAgentTabs).pipe(
-      Effect.repeat(Schedule.spaced(IDLE_SWEEP_INTERVAL)),
-      Effect.forkScoped,
-    );
-    const environmentId = yield* environment.getEnvironmentId;
-    const hostSession = broker
-      .connect(
-        {
-          clientId: SERVER_HOST_CLIENT_ID,
-          environmentId,
-          supportedOperations: [...PREVIEW_AUTOMATION_SERVER_OPERATIONS],
-        },
-        { preferred: true },
-      )
-      .pipe(
-        Effect.flatMap((events) =>
-          events.pipe(
-            Stream.runForEach((event) => {
-              if (event.type === "connected") {
-                hostConnectionId = event.connectionId;
-                return Effect.sync(reportLiveTabs);
-              }
-              return handleRequest(event.connectionId, event.request).pipe(
-                Effect.forkScoped,
-                Effect.asVoid,
-              );
-            }),
-          ),
+  yield* manager.events.pipe(Stream.runForEach(mirrorManagerEvent), Effect.forkScoped);
+  yield* Effect.sync(closeIdleAgentTabs).pipe(
+    Effect.repeat(Schedule.spaced(IDLE_SWEEP_INTERVAL)),
+    Effect.forkScoped,
+  );
+  const environmentId = yield* environment.getEnvironmentId;
+  const hostSession = broker
+    .connect(
+      {
+        clientId: SERVER_HOST_CLIENT_ID,
+        environmentId,
+        supportedOperations: [...PREVIEW_AUTOMATION_SERVER_OPERATIONS],
+      },
+      { preferred: true },
+    )
+    .pipe(
+      Effect.flatMap((events) =>
+        events.pipe(
+          Stream.runForEach((event) => {
+            if (event.type === "connected") {
+              hostConnectionId = event.connectionId;
+              return Effect.sync(reportLiveTabs);
+            }
+            return handleRequest(event.connectionId, event.request).pipe(
+              Effect.forkScoped,
+              Effect.asVoid,
+            );
+          }),
         ),
-      );
-    // The broker disconnects timed-out hosts, including slow first installs. Reconnect.
-    yield* hostSession.pipe(
-      Effect.exit,
-      Effect.andThen(Effect.sleep(HOST_RECONNECT_DELAY)),
-      Effect.forever,
-      Effect.forkScoped,
-    );
-    yield* Effect.addFinalizer(() =>
-      Effect.promise(async () => {
-        await contexts.close();
-      }),
+      ),
     );
-  }
+  // The broker disconnects timed-out hosts, including slow first installs. Reconnect.
+  yield* hostSession.pipe(
+    Effect.exit,
+    Effect.andThen(Effect.sleep(HOST_RECONNECT_DELAY)),
+    Effect.forever,
+    Effect.forkScoped,
+  );
+  yield* Effect.addFinalizer(() =>
+    Effect.promise(async () => {
+      await contexts.close();
+    }),
+  );
 
   const clearProfile = (profileId: string) =>
     Effect.tryPromise({
@@ -1988,7 +1983,6 @@ const make = Effect.gen(function* () {
     });
 
   return ServerBrowser.of({
-    enabled,
     attachViewer,
     clearProfile,
     openDownload,

apps/server/src/preview/ServerBrowserStream.test.ts

@@ -82,7 +82,6 @@ it.effect.each([
       ack: Effect.sync(() => acked.resolve()),
     });
     const browser = ServerBrowser.ServerBrowser.of({
-      enabled: true,
       clearProfile: () => Effect.void,
       openDownload: () => Effect.succeedNone,
       answerFileChooser: () => Effect.succeed(false),
@@ -159,7 +158,6 @@ it.effect.each([
     const auth = makeAuth(testCase.scopes, testCase.error);
     let attachments = 0;
     const browser = ServerBrowser.ServerBrowser.of({
-      enabled: true,
       clearProfile: () => Effect.void,
       openDownload: () => Effect.succeedNone,
       answerFileChooser: () => Effect.succeed(false),
@@ -200,7 +198,6 @@ it.effect("serves a tab's download only to an authorized session", () =>
     yield* fs.writeFileString(path, "report contents");
     const requests: Array<unknown> = [];
     const browser = ServerBrowser.ServerBrowser.of({
-      enabled: true,
       clearProfile: () => Effect.void,
       openDownload: (input) =>
         Effect.sync(() => {
@@ -248,7 +245,6 @@ it.effect("passes uploaded files to the page's open picker and needs operate sco
   Effect.gen(function* () {
     const answers: Array<{ chooserId: string; files: Array<{ name: string; text: string }> }> = [];
     const browser = ServerBrowser.ServerBrowser.of({
-      enabled: true,
       clearProfile: () => Effect.void,
       openDownload: () => Effect.succeedNone,
       answerFileChooser: (input) =>

apps/server/src/preview/ServerBrowserStream.ts

@@ -69,7 +69,7 @@ const makeHandler = (browser: ServerBrowser.ServerBrowser["Service"]) =>
       params.get("interactive") !== "false";
     const threadId = params.get("threadId") ?? "";
     const tabId = params.get("tabId") ?? "";
-    if (!browser.enabled || threadId.length === 0 || tabId.length === 0) {
+    if (threadId.length === 0 || tabId.length === 0) {
       return HttpServerResponse.text("Not Found", { status: 404 });
     }
     return yield* Effect.scoped(

apps/server/src/preview/serverBrowserEnabled.ts

@@ -177,13 +177,11 @@ For Antigravity's Google callback on a remote host, see
 On an environment started with `t3 serve` or `npx t3`, browser tabs run on the
 host instead of your device. You can watch and use them from a phone or any
 other browser. Agents keep using them while no device is connected, and
-`localhost` addresses reach servers on the host. The desktop app's own
-environment keeps using the desktop browser.
+`localhost` addresses reach servers on the host.
 
 The first tab downloads a headless Chromium and fonts, about 120 MB, into the
 T3 home. To use a browser already installed on the host, set
-`T3CODE_PREVIEW_BROWSER_PATH` to its executable. Set `T3CODE_SERVER_BROWSER=0`
-to turn host browser tabs off.
+`T3CODE_PREVIEW_BROWSER_PATH` to its executable.
 
 Agent tabs have separate storage and share a Chromium process. Take control before
 typing into an agent's tab, then release control when you want the agent to