fix(client): preserve prefs on logout; recover from initial-sync failure (N98/N99)

- N98: logoutClient and handleLogout now call removeFallbackSession() (removes
  only the 4 session credential keys) instead of window.localStorage.clear(),
  so settings, unsent drafts, PiP position, and status are preserved across a
  normal logout. localStorage.clear() stays reserved for clearLoginData() (the
  explicit factory-reset path).
- N99: the useSyncState callback now handles ERROR/STOPPED. A sync failure
  before the first PREPARED (offline at startup, homeserver unreachable) shows
  a dedicated error splash with a Retry button (startMatrix) instead of an
  endless "Heating up" spinner alongside a contradictory "Connection Lost!"
  banner. Guarded by a hasPreparedRef so post-PREPARED transient errors still
  go through <SyncStatus>; PREPARED self-heals the splash on recovery, and the
  redundant banner is suppressed while the splash is shown.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/pages/client/ClientRoot.tsx

@@ -15,7 +15,14 @@ import {
 } from 'folds';
 import { HttpApiEvent, HttpApiEventHandlerMap, MatrixClient } from 'matrix-js-sdk';
 import FocusTrap from 'focus-trap-react';
-import React, { MouseEventHandler, ReactNode, useCallback, useEffect, useState } from 'react';
+import React, {
+  MouseEventHandler,
+  ReactNode,
+  useCallback,
+  useEffect,
+  useRef,
+  useState,
+} from 'react';
 import {
   clearCacheAndReload,
   clearLoginData,
@@ -35,7 +42,7 @@ import { useSyncState } from '../../hooks/useSyncState';
 import { stopPropagation } from '../../utils/keyboard';
 import { SyncStatus } from './SyncStatus';
 import { AuthMetadataProvider } from '../../hooks/useAuthMetadata';
-import { getFallbackSession } from '../../state/sessions';
+import { getFallbackSession, removeFallbackSession } from '../../state/sessions';
 import { AutoDiscovery } from './AutoDiscovery';
 
 function ClientRootLoading() {
@@ -130,7 +137,10 @@ const useLogoutListener = (mx?: MatrixClient) => {
     const handleLogout: HttpApiEventHandlerMap[HttpApiEvent.SessionLoggedOut] = async () => {
       mx?.stopClient();
       await mx?.clearStores();
-      window.localStorage.clear();
+      // Remove only the session credential keys — NOT settings, drafts, and
+      // other preferences (N98). The SDK's IndexedDB stores are cleared above;
+      // window.localStorage.clear() is reserved for the explicit reset path.
+      removeFallbackSession();
       window.location.reload();
     };
 
@@ -146,6 +156,11 @@ type ClientRootProps = {
 };
 export function ClientRoot({ children }: ClientRootProps) {
   const [loading, setLoading] = useState(true);
+  const [syncError, setSyncError] = useState(false);
+  // Tracks whether the initial sync has ever reached PREPARED. After that,
+  // transient sync errors are handled by <SyncStatus>'s reconnection banner,
+  // so we must NOT pop the blocking error splash for them.
+  const hasPreparedRef = useRef(false);
   const { baseUrl, userId } = getFallbackSession() ?? {};
 
   const [loadState, loadMatrix] = useAsyncCallback<MatrixClient, Error, []>(
@@ -180,7 +195,14 @@ export function ClientRoot({ children }: ClientRootProps) {
     mx,
     useCallback((state) => {
       if (state === 'PREPARED') {
+        hasPreparedRef.current = true;
+        setSyncError(false);
         setLoading(false);
+      } else if (state === 'ERROR' || state === 'STOPPED') {
+        // Only surface the blocking error splash when the INITIAL sync fails
+        // (offline at startup, homeserver unreachable, non-retryable /sync
+        // error). After the first PREPARED, <SyncStatus> owns reconnection UX.
+        if (!hasPreparedRef.current) setSyncError(true);
       }
     }, []),
   );
@@ -188,9 +210,11 @@ export function ClientRoot({ children }: ClientRootProps) {
   return (
     <AutoDiscovery userId={userId!} baseUrl={baseUrl!}>
       <SpecVersions baseUrl={baseUrl!}>
-        {mx && <SyncStatus mx={mx} />}
+        {mx && !syncError && <SyncStatus mx={mx} />}
         {loading && <ClientRootOptions mx={mx} />}
-        {(loadState.status === AsyncStatus.Error || startState.status === AsyncStatus.Error) && (
+        {(loadState.status === AsyncStatus.Error ||
+          startState.status === AsyncStatus.Error ||
+          syncError) && (
           <SplashScreen>
             <Box
               direction="Column"
@@ -223,6 +247,13 @@ export function ClientRoot({ children }: ClientRootProps) {
                   {startState.status === AsyncStatus.Error && (
                     <Text>{`Failed to start. ${startState.error.message}`}</Text>
                   )}
+                  {syncError &&
+                    loadState.status !== AsyncStatus.Error &&
+                    startState.status !== AsyncStatus.Error && (
+                      <Text>
+                        Failed to sync with your homeserver. Check your connection and try again.
+                      </Text>
+                    )}
                   {('error' in loadState ? (loadState as any).error?.message : undefined) !==
                     IDB_VERSION_CONFLICT && (
                     <Button variant="Critical" onClick={mx ? () => startMatrix(mx) : loadMatrix}>