feat: default sidebar v2 on for nightly and dev builds

apps/desktop/src/settings/DesktopClientSettings.test.ts

@@ -30,6 +30,7 @@ const clientSettings: ClientSettings = {
   sidebarThreadSortOrder: "created_at",
   sidebarThreadPreviewCount: 6,
   sidebarV2Enabled: false,
+  sidebarV2ConfiguredByUser: false,
   timestampFormat: "24-hour",
   wordWrap: true,
 };

apps/mobile/src/features/home/HomeHeader.tsx

@@ -1,7 +1,5 @@
 import type { EnvironmentId, SidebarThreadSortOrder } from "@t3tools/contracts";
 import type { MenuAction } from "@react-native-menu/menu";
-import { useAtomValue } from "@effect/atom-react";
-import { AsyncResult } from "effect/unstable/reactivity";
 import { NativeHeaderToolbar, NativeStackScreenOptions } from "../../native/StackHeader";
 import { useCallback, useMemo, useRef } from "react";
 import { Platform, Pressable, Text as RNText, TextInput, View } from "react-native";
@@ -12,7 +10,7 @@ import { ControlPillMenu } from "../../components/ControlPill";
 import { SymbolView } from "../../components/AppSymbol";
 import { T3Wordmark } from "../../components/T3Wordmark";
 import { useThemeColor } from "../../lib/useThemeColor";
-import { mobilePreferencesAtom } from "../../state/preferences";
+import { useThreadListV2Enabled } from "../threads/use-thread-list-v2-enabled";
 import { useHardwareKeyboardCommand } from "../keyboard/hardwareKeyboardCommands";
 import { withNativeGlassHeaderItem } from "../layout/native-glass-header-items";
 import { createNativeMailSearchToolbarItem } from "../layout/native-mail-search-toolbar";
@@ -59,21 +57,14 @@ function checkedMenuState(checked: boolean) {
   return checked ? ("on" as const) : undefined;
 }
 
-/** Thread List v2 lays the list out in fixed creation order, so the
-    sort/group filter controls would be silently ignored — hide them and
-    key the "customized" icon state off the environment filter alone. */
-function useThreadListV2FilterGate() {
-  const preferencesResult = useAtomValue(mobilePreferencesAtom);
-  return (
-    AsyncResult.isSuccess(preferencesResult) && preferencesResult.value.threadListV2Enabled === true
-  );
-}
-
 function AndroidHomeHeader(props: HomeHeaderProps) {
   const insets = useSafeAreaInsets();
   const iconColor = useThemeColor("--color-icon");
   const mutedColor = useThemeColor("--color-foreground-muted");
-  const threadListV2Enabled = useThreadListV2FilterGate();
+  // Thread List v2 lays the list out in fixed creation order, so the
+  // sort/group filter controls would be silently ignored — hide them and
+  // key the "customized" icon state off the environment filter alone.
+  const threadListV2Enabled = useThreadListV2Enabled();
   const hasCustomListOptions = threadListV2Enabled
     ? props.selectedEnvironmentId !== null || props.selectedProjectKey !== null
     : hasCustomHomeListOptions(props);
@@ -291,7 +282,10 @@ function AndroidHomeHeader(props: HomeHeaderProps) {
 function IosHomeHeader(props: HomeHeaderProps) {
   const searchBarRef = useRef<SearchBarCommands>(null);
   const iconColor = useThemeColor("--color-icon");
-  const threadListV2Enabled = useThreadListV2FilterGate();
+  // Thread List v2 lays the list out in fixed creation order, so the
+  // sort/group filter controls would be silently ignored — hide them and
+  // key the "customized" icon state off the environment filter alone.
+  const threadListV2Enabled = useThreadListV2Enabled();
   const hasCustomListOptions = threadListV2Enabled
     ? props.selectedEnvironmentId !== null || props.selectedProjectKey !== null
     : hasCustomHomeListOptions(props);

apps/mobile/src/features/home/HomeScreen.tsx

@@ -27,6 +27,7 @@ import type { SavedRemoteConnection } from "../../lib/connection";
 import { scopedProjectKey } from "../../lib/scopedEntities";
 import { NATIVE_LIQUID_GLASS_SUPPORTED } from "../../native/native-glass";
 import { mobilePreferencesAtom, updateMobilePreferencesAtom } from "../../state/preferences";
+import { useThreadListV2Enabled } from "../threads/use-thread-list-v2-enabled";
 import { environmentServerConfigsAtom } from "../../state/server";
 import type { PendingNewTask } from "../../state/use-pending-new-tasks";
 import {
@@ -181,9 +182,7 @@ export function HomeScreen(props: HomeScreenProps) {
     ReadonlyMap<string, HomeGroupDisplayState>
   >(() => new Map());
   const preferencesResult = useAtomValue(mobilePreferencesAtom);
-  const threadListV2Enabled =
-    AsyncResult.isSuccess(preferencesResult) &&
-    preferencesResult.value.threadListV2Enabled === true;
+  const threadListV2Enabled = useThreadListV2Enabled();
   const savePreferences = useAtomSet(updateMobilePreferencesAtom);
   const openSwipeableRef = useRef<SwipeableMethods | null>(null);
   const listRef = useRef<LegendListRef | null>(null);

apps/mobile/src/features/settings/SettingsRouteScreen.tsx

@@ -37,6 +37,7 @@ import { WorkspaceSidebarToolbar } from "../layout/workspace-sidebar-toolbar";
 import { runtime } from "../../lib/runtime";
 import { useThemeColor } from "../../lib/useThemeColor";
 import { mobilePreferencesAtom, updateMobilePreferencesAtom } from "../../state/preferences";
+import { useThreadListV2Enabled } from "../threads/use-thread-list-v2-enabled";
 import { useSavedRemoteConnections } from "../../state/use-remote-environment-registry";
 import { SettingsRow } from "./components/SettingsRow";
 import { SettingsSection } from "./components/SettingsSection";
@@ -546,11 +547,8 @@ function GeneralSettingsSection() {
  * the counterpart of web's Settings → Beta backed by mobile preferences.
  */
 function BetaSettingsSection() {
-  const preferencesResult = useAtomValue(mobilePreferencesAtom);
   const savePreferences = useAtomSet(updateMobilePreferencesAtom);
-  const threadListV2Enabled = AsyncResult.isSuccess(preferencesResult)
-    ? preferencesResult.value.threadListV2Enabled === true
-    : false;
+  const threadListV2Enabled = useThreadListV2Enabled();
 
   return (
     <View className="gap-3">

apps/mobile/src/features/threads/ThreadNavigationSidebar.tsx

@@ -6,7 +6,6 @@ import type {
 import { LegendList } from "@legendapp/list/react-native";
 import type { MenuAction } from "@react-native-menu/menu";
 import { useAtomValue } from "@effect/atom-react";
-import { AsyncResult } from "effect/unstable/reactivity";
 import type { EnvironmentId } from "@t3tools/contracts";
 import { useCallback, useEffect, useMemo, useRef, useState, type ReactNode } from "react";
 import type { LayoutChangeEvent, NativeScrollEvent, NativeSyntheticEvent } from "react-native";
@@ -25,7 +24,7 @@ import { NativeStackScreenOptions } from "../../native/StackHeader";
 import { scopedProjectKey, scopedThreadKey } from "../../lib/scopedEntities";
 import { useThemeColor } from "../../lib/useThemeColor";
 import { useProjects, useThreadShells } from "../../state/entities";
-import { mobilePreferencesAtom } from "../../state/preferences";
+import { useThreadListV2Enabled } from "./use-thread-list-v2-enabled";
 import { environmentServerConfigsAtom } from "../../state/server";
 import { usePendingNewTasks, type PendingNewTask } from "../../state/use-pending-new-tasks";
 import { useWorkspaceState } from "../../state/workspace";
@@ -196,10 +195,7 @@ function ThreadNavigationSidebarPane(
   const sidebarScrollGesture = useMemo(() => Gesture.Native(), []);
   const { archiveThread, confirmDeleteThread, settleThread, unsettleThread } =
     useThreadListActions();
-  const preferencesResult = useAtomValue(mobilePreferencesAtom);
-  const threadListV2Enabled =
-    AsyncResult.isSuccess(preferencesResult) &&
-    preferencesResult.value.threadListV2Enabled === true;
+  const threadListV2Enabled = useThreadListV2Enabled();
   const pendingTasks = usePendingNewTasks();
   const { openPendingTask, confirmDeletePendingTask } = usePendingTaskListActions();
   const environments = useMemo(

apps/mobile/src/features/threads/threadListV2.test.ts

@@ -4,6 +4,7 @@ import { describe, expect, it } from "vite-plus/test";
 
 import {
   buildThreadListV2Items,
+  resolveThreadListV2Enabled,
   resolveThreadListV2Status,
   sortThreadsForListV2,
 } from "./threadListV2";
@@ -38,6 +39,21 @@ function makeThread(
 
 const NOW = "2026-06-02T00:00:00.000Z";
 
+describe("resolveThreadListV2Enabled", () => {
+  it.each(["development", "preview"])("defaults on for the %s variant", (appVariant) => {
+    expect(resolveThreadListV2Enabled({ preference: undefined, appVariant })).toBe(true);
+  });
+
+  it.each(["production", undefined])("defaults off for the %s variant", (appVariant) => {
+    expect(resolveThreadListV2Enabled({ preference: undefined, appVariant })).toBe(false);
+  });
+
+  it("prefers an explicit device choice over the variant default", () => {
+    expect(resolveThreadListV2Enabled({ preference: false, appVariant: "preview" })).toBe(false);
+    expect(resolveThreadListV2Enabled({ preference: true, appVariant: "production" })).toBe(true);
+  });
+});
+
 describe("resolveThreadListV2Status", () => {
   it("prioritizes approval over a running session", () => {
     const thread = makeThread({

apps/mobile/src/features/threads/threadListV2.ts

@@ -18,6 +18,27 @@ export type ThreadListV2Status = "approval" | "input" | "working" | "failed" | "
 export const THREAD_LIST_V2_SETTLED_INITIAL_COUNT = 10;
 export const THREAD_LIST_V2_SETTLED_PAGE_COUNT = 25;
 
+/**
+ * Whether Thread List v2 is on by default for an app variant. The `development`
+ * and `preview` variants are mobile's nightly equivalents and opt in;
+ * `production` stays on v1. Counterpart of web's `resolveSidebarV2Default`.
+ */
+export function resolveThreadListV2Default(appVariant: unknown): boolean {
+  return appVariant === "development" || appVariant === "preview";
+}
+
+/**
+ * Resolved Thread List v2 state: the device-local preference if the user has
+ * set one, otherwise the default for this app variant. Preferences persist as
+ * sparse patches, so `undefined` genuinely means "never chosen".
+ */
+export function resolveThreadListV2Enabled(input: {
+  readonly preference: boolean | undefined;
+  readonly appVariant: unknown;
+}): boolean {
+  return input.preference ?? resolveThreadListV2Default(input.appVariant);
+}
+
 export function resolveThreadListV2Status(
   thread: Pick<EnvironmentThreadShell, "hasPendingApprovals" | "hasPendingUserInput" | "session">,
 ): ThreadListV2Status {

apps/mobile/src/features/threads/use-thread-list-v2-enabled.ts

@@ -0,0 +1,25 @@
+import { useAtomValue } from "@effect/atom-react";
+import { AsyncResult } from "effect/unstable/reactivity";
+import Constants from "expo-constants";
+
+import { mobilePreferencesAtom } from "../../state/preferences";
+import { resolveThreadListV2Enabled } from "./threadListV2";
+
+/**
+ * Resolved Thread List v2 state: the device-local preference if the user has
+ * set one, otherwise the default for this app variant (on for development and
+ * preview, off for production). Every consumer must read through this rather
+ * than the raw preference, which is undefined until explicitly chosen.
+ *
+ * Kept out of `state/preferences.ts` so that module stays importable from node
+ * test environments, which have no `__DEV__` for expo-constants.
+ */
+export function useThreadListV2Enabled(): boolean {
+  const preferencesResult = useAtomValue(mobilePreferencesAtom);
+  return resolveThreadListV2Enabled({
+    preference: AsyncResult.isSuccess(preferencesResult)
+      ? preferencesResult.value.threadListV2Enabled
+      : undefined,
+    appVariant: Constants.expoConfig?.extra?.appVariant,
+  });
+}

apps/mobile/src/persistence/mobile-preferences.ts

@@ -26,7 +26,8 @@ export interface Preferences {
   /**
    * Device-local mirror of the web beta's `sidebarV2Enabled`. Mobile has no
    * client-settings sync, so the flat v2 thread list is opted into per
-   * device.
+   * device. Undefined means the user has never chosen, in which case the app
+   * variant decides — see `resolveThreadListV2Enabled`.
    */
   readonly threadListV2Enabled?: boolean;
 }

apps/web/src/branding.logic.ts

@@ -11,6 +11,19 @@ export function formatAppDisplayName(input: {
   return `${input.baseName} (${input.stageLabel})`;
 }
 
+/**
+ * Whether the sidebar v2 beta is on by default for a build stage.
+ *
+ * Nightly and local dev opt in; Alpha and Latest stay on v1. This is resolved
+ * from the client's own stage label rather than the connected server's version:
+ * v2 only exists in the client, so a stable client on a nightly server has
+ * nothing to turn on.
+ */
+export function resolveSidebarV2Default(stageLabel: string): boolean {
+  const stage = stageLabel.trim().toLowerCase();
+  return stage === "nightly" || stage === "dev";
+}
+
 export function resolveServerBackedAppStageLabel(input: {
   readonly primaryServerVersion: string | null | undefined;
   readonly fallbackStageLabel: string;

apps/web/src/branding.test.ts

@@ -2,6 +2,7 @@ import { afterEach, describe, expect, it, vi } from "vite-plus/test";
 import {
   resolveServerBackedAppDisplayName,
   resolveServerBackedAppStageLabel,
+  resolveSidebarV2Default,
 } from "./branding.logic";
 
 const originalWindow = globalThis.window;
@@ -114,3 +115,13 @@ describe("branding logic", () => {
     ).toBe("T3 Code (Alpha)");
   });
 });
+
+describe("resolveSidebarV2Default", () => {
+  it.each(["Nightly", "Dev", "nightly", " dev "])("enables the beta for %s builds", (stage) => {
+    expect(resolveSidebarV2Default(stage)).toBe(true);
+  });
+
+  it.each(["Alpha", "Latest", ""])("leaves the beta off for %s builds", (stage) => {
+    expect(resolveSidebarV2Default(stage)).toBe(false);
+  });
+});

apps/web/src/components/AppSidebarLayout.tsx

@@ -8,7 +8,7 @@ import { getLocalStorageItem } from "../hooks/useLocalStorage";
 import { resolveShortcutCommand, shortcutLabelForCommand } from "../keybindings";
 import { cn, isMacPlatform } from "../lib/utils";
 import { primaryServerKeybindingsAtom } from "../state/server";
-import { useClientSettings } from "../hooks/useSettings";
+import { useSidebarV2Enabled } from "../hooks/useSettings";
 import ThreadSidebar from "./Sidebar";
 import ThreadSidebarV2 from "./SidebarV2";
 import { useSidebarStageBackdropVariant } from "./SidebarStageBackdrop";
@@ -100,7 +100,7 @@ function SidebarControl() {
 
 export function AppSidebarLayout({ children }: { children: ReactNode }) {
   const navigate = useNavigate();
-  const sidebarV2Enabled = useClientSettings((settings) => settings.sidebarV2Enabled);
+  const sidebarV2Enabled = useSidebarV2Enabled();
   // Settings routes render the settings nav, which lives in the v1 component
   // and is identical for both sidebars — so v1 stays mounted there.
   const pathname = useLocation({ select: (location) => location.pathname });

apps/web/src/components/settings/BetaSettingsPanel.tsx

@@ -1,6 +1,10 @@
 import { useEffect, useState } from "react";
 
-import { useClientSettings, useUpdateClientSettings } from "../../hooks/useSettings";
+import {
+  useClientSettings,
+  useSidebarV2Enabled,
+  useUpdateClientSettings,
+} from "../../hooks/useSettings";
 import { Input } from "../ui/input";
 import { Switch } from "../ui/switch";
 import { SettingsPageContainer, SettingsRow, SettingsSection } from "./settingsLayout";
@@ -51,7 +55,7 @@ function AutoSettleDaysInput({
 }
 
 export function BetaSettingsPanel() {
-  const sidebarV2Enabled = useClientSettings((settings) => settings.sidebarV2Enabled);
+  const sidebarV2Enabled = useSidebarV2Enabled();
   const sidebarAutoSettleAfterDays = useClientSettings(
     (settings) => settings.sidebarAutoSettleAfterDays,
   );
@@ -66,7 +70,14 @@ export function BetaSettingsPanel() {
           control={
             <Switch
               checked={sidebarV2Enabled}
-              onCheckedChange={(checked) => updateSettings({ sidebarV2Enabled: Boolean(checked) })}
+              // Touching the switch pins the choice, so a nightly build that
+              // defaults v2 on does not flip it back after the user opts out.
+              onCheckedChange={(checked) =>
+                updateSettings({
+                  sidebarV2Enabled: Boolean(checked),
+                  sidebarV2ConfiguredByUser: true,
+                })
+              }
               aria-label="Enable the sidebar v2 beta"
             />
           }

apps/web/src/hooks/useSettings.ts

@@ -24,6 +24,8 @@ import {
   type UnifiedSettings,
 } from "@t3tools/contracts/settings";
 import { safeErrorLogAttributes } from "@t3tools/client-runtime/errors";
+import { APP_STAGE_LABEL } from "~/branding";
+import { resolveSidebarV2Default } from "~/branding.logic";
 import { ensureLocalApi } from "~/localApi";
 import * as Struct from "effect/Struct";
 import { primaryServerSettingsAtom, serverEnvironment } from "~/state/server";
@@ -218,6 +220,21 @@ export function useClientSettings<T = ClientSettings>(
   return useMemo(() => (selector ? selector(settings) : (settings as T)), [selector, settings]);
 }
 
+/**
+ * Resolved sidebar v2 state: an explicit choice in Settings → Beta if the user
+ * has made one, otherwise the default for this build stage (on for nightly and
+ * dev, off for production). Every consumer must read through this rather than
+ * `settings.sidebarV2Enabled`, which is only meaningful alongside
+ * `sidebarV2ConfiguredByUser`.
+ */
+export function useSidebarV2Enabled(): boolean {
+  return useClientSettings((settings) =>
+    settings.sidebarV2ConfiguredByUser
+      ? settings.sidebarV2Enabled
+      : resolveSidebarV2Default(APP_STAGE_LABEL),
+  );
+}
+
 /** Read current settings for one environment, merged with client-local preferences. */
 export function useEnvironmentSettings<T = UnifiedSettings>(
   environmentId: EnvironmentId,

apps/web/src/routes/_chat.tsx

@@ -3,7 +3,7 @@ import { useAtomValue } from "@effect/atom-react";
 import { useEffect, useMemo } from "react";
 
 import { isCommandPaletteOpen } from "../commandPaletteBus";
-import { useClientSettings } from "../hooks/useSettings";
+import { useClientSettings, useSidebarV2Enabled } from "../hooks/useSettings";
 import { openCommandPalette } from "../commandPaletteBus";
 import { useProjects } from "../state/entities";
 import { usePrimaryEnvironmentId } from "../state/environments";
@@ -28,7 +28,7 @@ function ChatRouteGlobalShortcuts() {
   const { activeDraftThread, activeThread, defaultProjectRef, handleNewThread, routeThreadRef } =
     useHandleNewThread();
   const keybindings = useAtomValue(primaryServerKeybindingsAtom);
-  const sidebarV2Enabled = useClientSettings((settings) => settings.sidebarV2Enabled);
+  const sidebarV2Enabled = useSidebarV2Enabled();
   const projectGroupingSettings = useClientSettings(selectProjectGroupingSettings);
   const projects = useProjects();
   const primaryEnvironmentId = usePrimaryEnvironmentId();

packages/contracts/src/settings.test.ts

@@ -56,6 +56,22 @@ describe("ClientSettings sidebar v2", () => {
     expect(settings.sidebarAutoSettleAfterDays).toBe(3);
   });
 
+  it("treats settings written before the beta had a per-channel default as unconfigured", () => {
+    // The stored blob always carries `sidebarV2Enabled`, so only the companion
+    // flag can distinguish "user opted out" from "never touched it".
+    expect(decodeClientSettings({ sidebarV2Enabled: false }).sidebarV2ConfiguredByUser).toBe(false);
+    expect(decodeClientSettings({ sidebarV2Enabled: true }).sidebarV2ConfiguredByUser).toBe(false);
+  });
+
+  it("preserves an explicit beta choice", () => {
+    const settings = decodeClientSettings({
+      sidebarV2Enabled: false,
+      sidebarV2ConfiguredByUser: true,
+    });
+    expect(settings.sidebarV2Enabled).toBe(false);
+    expect(settings.sidebarV2ConfiguredByUser).toBe(true);
+  });
+
   it("allows auto-settle by inactivity to be disabled", () => {
     expect(
       decodeClientSettings({ sidebarAutoSettleAfterDays: null }).sidebarAutoSettleAfterDays,