diff --git a/server/app/domains/remote_control/service/remote_control_service.py b/server/app/domains/remote_control/service/remote_control_service.py
index 8fb54d9e..bf6590dc 100644
--- a/server/app/domains/remote_control/service/remote_control_service.py
+++ b/server/app/domains/remote_control/service/remote_control_service.py
@@ -324,25 +324,40 @@ class RemoteControlService:
             return RemoteControlService._get_owned_space(user_id, history.space_id, db)
         return None
 
+    @staticmethod
+    def _ensure_remote_control_supported_space(space: Space) -> None:
+        if space.source_type == SpaceSourceType.LEGACY:
+            raise HTTPException(
+                status_code=400,
+                detail={
+                    "code": "REMOTE_CONTROL_LEGACY_SPACE_UNSUPPORTED",
+                    "message": "Legacy Spaces do not support remote control.",
+                },
+            )
+
     @staticmethod
     def _session_space(session: RemoteControlSession, user_id: int, db: Session) -> Space:
         if session.space_id:
-            return RemoteControlService._get_owned_space(user_id, session.space_id, db)
+            space = RemoteControlService._get_owned_space(user_id, session.space_id, db)
+            RemoteControlService._ensure_remote_control_supported_space(space)
+            return space
         project_id, _, _, _ = RemoteControlService._effective_target(session)
         if project_id:
             space = RemoteControlService._space_for_project(user_id, project_id, db)
             if space:
+                RemoteControlService._ensure_remote_control_supported_space(space)
                 session.space_id = space.id
                 session.space_name_snapshot = space.name
                 db.add(session)
                 db.flush()
                 return space
-        space = SpaceService.ensure_legacy_space(user_id, db)
-        session.space_id = space.id
-        session.space_name_snapshot = space.name
-        db.add(session)
-        db.flush()
-        return space
+        raise HTTPException(
+            status_code=400,
+            detail={
+                "code": "REMOTE_CONTROL_SPACE_REQUIRED",
+                "message": "Remote control requires a non-legacy Space.",
+            },
+        )
 
     @staticmethod
     def _ensure_folder_space(space: Space) -> None:
@@ -515,9 +530,22 @@ class RemoteControlService:
         elif target_project_id:
             space = RemoteControlService._space_for_project(user_id, target_project_id, db)
             if not space:
-                space = SpaceService.ensure_legacy_space(user_id, db)
+                raise HTTPException(
+                    status_code=400,
+                    detail={
+                        "code": "REMOTE_CONTROL_SPACE_REQUIRED",
+                        "message": "Remote control requires a non-legacy Space.",
+                    },
+                )
         else:
-            space = SpaceService.ensure_legacy_space(user_id, db)
+            raise HTTPException(
+                status_code=400,
+                detail={
+                    "code": "REMOTE_CONTROL_SPACE_REQUIRED",
+                    "message": "Remote control requires a non-legacy Space.",
+                },
+            )
+        RemoteControlService._ensure_remote_control_supported_space(space)
         if target_project_id:
             project = RemoteControlService._get_owned_project(user_id, target_project_id, db)
             if project and project.space_id != space.id:
diff --git a/server/app/domains/space/service/space_service.py b/server/app/domains/space/service/space_service.py
index e6aac4a1..79ba47cd 100644
--- a/server/app/domains/space/service/space_service.py
+++ b/server/app/domains/space/service/space_service.py
@@ -29,6 +29,7 @@ from app.model.project import (
     Project,
     ProjectIn,
     ProjectOut,
+    ProjectStatus,
     ProjectUpdate,
     ProjectWorkdirMode,
 )
@@ -506,12 +507,31 @@ class SpaceService:
     @staticmethod
     def list_spaces(user_id: int | str, s: Session) -> list[SpaceOut]:
         canonical_user_id = SpaceService.canonical_user_id(user_id)
-        SpaceService.ensure_legacy_space(canonical_user_id, s)
         spaces = s.exec(
             select(Space)
             .where(Space.user_id == canonical_user_id)
             .order_by(Space.updated_at.desc())
         ).all()
+        legacy_space_ids = [
+            space.id
+            for space in spaces
+            if space.source_type == SpaceSourceType.LEGACY
+        ]
+        if legacy_space_ids:
+            legacy_space_ids_with_projects = set(
+                s.exec(
+                    select(Project.space_id)
+                    .where(Project.user_id == canonical_user_id)
+                    .where(Project.space_id.in_(legacy_space_ids))
+                    .where(Project.status != ProjectStatus.ARCHIVED)
+                ).all()
+            )
+            spaces = [
+                space
+                for space in spaces
+                if space.source_type != SpaceSourceType.LEGACY
+                or space.id in legacy_space_ids_with_projects
+            ]
         return [SpaceOut.from_model(space) for space in spaces]
 
     @staticmethod
diff --git a/server/tests/test_space_legacy_behavior.py b/server/tests/test_space_legacy_behavior.py
new file mode 100644
index 00000000..f0b2522f
--- /dev/null
+++ b/server/tests/test_space_legacy_behavior.py
@@ -0,0 +1,112 @@
+# ========= Copyright 2025-2026 @ Eigent.ai All Rights Reserved. =========
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+# ========= Copyright 2025-2026 @ Eigent.ai All Rights Reserved. =========
+
+from types import SimpleNamespace
+
+import pytest
+from fastapi import HTTPException
+
+from app.domains.remote_control.service.remote_control_service import RemoteControlService
+from app.domains.space.service.space_service import SpaceService
+from app.model.space.space import SpaceSourceType
+
+
+class _ExecResult:
+    def __init__(self, rows):
+        self._rows = rows
+
+    def all(self):
+        return self._rows
+
+
+class _ListSpacesSession:
+    def __init__(self, rows=None, project_space_ids=None):
+        self._rows = rows or []
+        self._project_space_ids = project_space_ids or []
+        self._exec_count = 0
+
+    def exec(self, _statement):
+        self._exec_count += 1
+        if self._exec_count > 1:
+            return _ExecResult(self._project_space_ids)
+        return _ExecResult(self._rows)
+
+
+def _space(
+    space_id: str,
+    source_type: str,
+    *,
+    user_id: str = "user_new",
+    name: str = "Untitled Space",
+):
+    return SimpleNamespace(
+        id=space_id,
+        user_id=user_id,
+        name=name,
+        description=None,
+        source_type=source_type,
+        root_path=None,
+        root_fingerprint=None,
+        status="active",
+        schema_version=1,
+        metadata_json={"legacy": True} if source_type == SpaceSourceType.LEGACY else None,
+        created_at=None,
+        updated_at=None,
+    )
+
+
+def test_list_spaces_does_not_create_legacy_for_empty_user(monkeypatch):
+    def fail_ensure(*_args, **_kwargs):
+        raise AssertionError("list_spaces must not create Legacy Space")
+
+    monkeypatch.setattr(SpaceService, "ensure_legacy_space", fail_ensure)
+
+    assert SpaceService.list_spaces("user_new", _ListSpacesSession()) == []
+
+
+def test_list_spaces_hides_empty_legacy_space():
+    spaces = [
+        _space("legacy_user_new", SpaceSourceType.LEGACY, name="Legacy Space"),
+        _space("space_new", SpaceSourceType.BLANK),
+    ]
+
+    result = SpaceService.list_spaces("user_new", _ListSpacesSession(spaces))
+
+    assert [space.id for space in result] == ["space_new"]
+
+
+def test_list_spaces_keeps_legacy_space_with_active_projects():
+    legacy_space = _space(
+        "legacy_user_old",
+        SpaceSourceType.LEGACY,
+        user_id="user_old",
+        name="Legacy Space",
+    )
+
+    result = SpaceService.list_spaces(
+        "user_old",
+        _ListSpacesSession([legacy_space], project_space_ids=["legacy_user_old"]),
+    )
+
+    assert [space.id for space in result] == ["legacy_user_old"]
+
+
+def test_remote_control_rejects_legacy_space():
+    with pytest.raises(HTTPException) as exc:
+        RemoteControlService._ensure_remote_control_supported_space(
+            SimpleNamespace(source_type=SpaceSourceType.LEGACY)
+        )
+
+    assert exc.value.status_code == 400
+    assert exc.value.detail["code"] == "REMOTE_CONTROL_LEGACY_SPACE_UNSUPPORTED"
diff --git a/src/components/Dispatch/index.tsx b/src/components/Dispatch/index.tsx
index 731d0b92..a1880d69 100644
--- a/src/components/Dispatch/index.tsx
+++ b/src/components/Dispatch/index.tsx
@@ -26,6 +26,7 @@ import {
   revokeRemoteControlSession,
   waitForRemoteControlBridgeConnected,
 } from '@/lib/remoteControl';
+import { canUseRemoteControlInSpace } from '@/lib/spaceLabel';
 import { cn } from '@/lib/utils';
 import { getConnectionConfig } from '@/store/connectionStore';
 import { useProjectRuntimeStore } from '@/store/projectRuntimeStore';
@@ -176,6 +177,7 @@ interface ChannelRowProps {
   icon?: React.ReactNode;
   imgSrc?: string;
   disabled?: boolean;
+  disabledLabel?: string;
   comingSoon?: boolean;
   hasActiveSessions?: boolean;
   loading?: boolean;
@@ -187,12 +189,14 @@ function ChannelRow({
   icon,
   imgSrc,
   disabled,
+  disabledLabel,
   comingSoon,
   hasActiveSessions,
   loading,
   onStart,
 }: ChannelRowProps) {
   const { t } = useTranslation();
+  const isDisabled = Boolean(disabled);
 
   return (
     <div
@@ -200,9 +204,9 @@ function ChannelRow({
         'group/row flex h-[44px] w-full cursor-default select-none items-center gap-3 rounded-xl',
         'border border-transparent bg-ds-bg-neutral-default-default px-3',
         'transition-colors duration-150',
-        !disabled && 'hover:border-ds-border-neutral-subtle-default',
+        !isDisabled && 'hover:border-ds-border-neutral-subtle-default',
         hasActiveSessions && 'border-ds-border-neutral-subtle-default',
-        disabled && 'cursor-not-allowed opacity-50'
+        isDisabled && 'cursor-not-allowed opacity-50'
       )}
     >
       <div className="flex shrink-0 items-center">
@@ -228,13 +232,19 @@ function ChannelRow({
           </span>
         )}
 
-        {!disabled && !comingSoon && hasActiveSessions && (
+        {isDisabled && !comingSoon && disabledLabel && (
+          <span className="shrink-0 rounded-full bg-ds-bg-neutral-muted-default px-2 py-0.5 text-label-xs text-ds-text-neutral-muted-default">
+            {disabledLabel}
+          </span>
+        )}
+
+        {!isDisabled && !comingSoon && hasActiveSessions && (
           <span className="shrink-0 rounded-full bg-ds-bg-success-subtle-default px-2 py-0.5 text-label-xs text-ds-text-success-strong-default">
             {t('layout.dispatch-connected', { defaultValue: 'Connected' })}
           </span>
         )}
 
-        {!disabled && !comingSoon && !hasActiveSessions && (
+        {!isDisabled && !comingSoon && !hasActiveSessions && (
           <Button
             type="button"
             variant="secondary"
@@ -332,6 +342,8 @@ export function WorkspaceDispatch() {
     s.activeSpaceId ? s.spaces[s.activeSpaceId] : null
   );
   const activeProjectId = useProjectRuntimeStore((s) => s.activeProjectId);
+  const remoteControlUnsupportedForSpace =
+    activeSpace !== null && !canUseRemoteControlInSpace(activeSpace);
 
   const activeSessions = useTriggerStore((s) => s.activeRemoteControlSessions);
   const logs = useTriggerStore((s) => s.remoteControlLogs);
@@ -416,6 +428,10 @@ export function WorkspaceDispatch() {
       toast.error('Open a Space before starting remote control.');
       return;
     }
+    if (!activeSpace || !canUseRemoteControlInSpace(activeSpace)) {
+      toast.error('Legacy Spaces do not support remote control.');
+      return;
+    }
 
     setRemoteControlLoading(true);
     try {
@@ -478,6 +494,7 @@ export function WorkspaceDispatch() {
     }
   }, [
     activeProjectId,
+    activeSpace,
     activeSpace?.name,
     activeSpaceId,
     addRemoteControlSession,
@@ -599,6 +616,10 @@ export function WorkspaceDispatch() {
           />
         }
         hasActiveSessions={hasActiveRemoteControl}
+        disabled={remoteControlUnsupportedForSpace && !hasActiveRemoteControl}
+        disabledLabel={t('layout.dispatch-unavailable', {
+          defaultValue: 'Unavailable',
+        })}
         loading={remoteControlLoading}
         onStart={() => void handleCreateRemoteControl()}
       />
diff --git a/src/lib/spaceLabel.ts b/src/lib/spaceLabel.ts
index e55f47bb..7e78ce72 100644
--- a/src/lib/spaceLabel.ts
+++ b/src/lib/spaceLabel.ts
@@ -65,6 +65,14 @@ export function canCreateProjectInSpace(
   return !isLegacySpace(space);
 }
 
+/** Remote control requires a regular Space target; legacy migration buckets are unsupported. */
+export function canUseRemoteControlInSpace(
+  space: Space | null | undefined
+): boolean {
+  if (!space) return false;
+  return !isLegacySpace(space);
+}
+
 /** Folder-backed and scratch Spaces with a local workspace root behave locally. */
 export function isLocalWorkspaceSpace(
   space: Space | null | undefined
diff --git a/src/store/authStore.ts b/src/store/authStore.ts
index 48a88bd3..5431d704 100644
--- a/src/store/authStore.ts
+++ b/src/store/authStore.ts
@@ -131,11 +131,13 @@ const getRandomDefaultModel = (): CloudModelType => {
 };
 
 const hydrateSpacesForUser = (userId: number | string | null | undefined) => {
+  if (!useSpaceStore?.getState) return;
   if (userId === null || userId === undefined || userId === '') {
+    useSpaceStore.getState().resetForUser(null);
     useSpaceStore.getState().ensureLegacySpace();
     return;
   }
-  useSpaceStore.getState().ensureLegacySpace(userId);
+  useSpaceStore.getState().resetForUser(userId);
   void useSpaceStore.getState().hydrateFromServer(userId);
 };
 
@@ -173,6 +175,11 @@ const authStore = create<AuthState>()(
 
       // auth related methods
       setAuth: ({ token, username, email, user_id }) => {
+        const previousUserId = get().user_id;
+        if (previousUserId != null && previousUserId !== user_id) {
+          void clearAllCachedProjects(previousUserId);
+        }
+        useSpaceStore.getState().resetForUser(user_id);
         set({ token, username, email, user_id });
         hydrateSpacesForUser(user_id);
       },
@@ -193,6 +200,7 @@ const authStore = create<AuthState>()(
           initState: 'carousel',
           localProxyValue: null,
         });
+        useSpaceStore.getState().resetForUser(null);
       },
 
       // set related methods
@@ -433,12 +441,9 @@ export const useAuthStore = authStore;
 export const getAuthStore = () => authStore.getState();
 
 queueMicrotask(() => {
-  const { token, user_id } = authStore.getState();
-  if (token) {
-    hydrateSpacesForUser(user_id);
-  } else {
-    useSpaceStore.getState().ensureLegacySpace(user_id);
-  }
+  if (!useSpaceStore?.getState) return;
+  const { user_id } = authStore.getState();
+  hydrateSpacesForUser(user_id);
 });
 
 // constant definition
diff --git a/src/store/spaceStore.test.ts b/src/store/spaceStore.test.ts
new file mode 100644
index 00000000..decbd18f
--- /dev/null
+++ b/src/store/spaceStore.test.ts
@@ -0,0 +1,196 @@
+// ========= Copyright 2025-2026 @ Eigent.ai All Rights Reserved. =========
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+// ========= Copyright 2025-2026 @ Eigent.ai All Rights Reserved. =========
+
+import { beforeEach, describe, expect, it, vi } from 'vitest';
+import {
+  SPACE_SCHEMA_VERSION,
+  type Space,
+  type SpaceSourceType,
+  useSpaceStore,
+} from './spaceStore';
+
+const authStoreMock = vi.hoisted(() => ({
+  state: {
+    user_id: 2,
+    email: 'new@example.com',
+  },
+}));
+
+vi.mock('@/store/authStore', () => ({
+  getAuthStore: () => authStoreMock.state,
+}));
+
+vi.mock('@/api/http', () => ({
+  proxyFetchGet: vi.fn().mockResolvedValue({ projects: [] }),
+}));
+
+vi.mock('@/service/spaceApi', () => ({
+  proxyCreateSpace: vi.fn(),
+  proxyEnsureLegacySpace: vi.fn(),
+  proxyFetchSpaceProjects: vi.fn(),
+  proxyFetchSpaces: vi.fn(),
+}));
+
+vi.mock('@/service/workspaceApi', () => ({
+  reconcileWorkspaceBindings: vi.fn().mockResolvedValue(undefined),
+}));
+
+const makeSpace = (
+  id: string,
+  name: string,
+  sourceType: SpaceSourceType,
+  userId = '2',
+  metadata?: Space['metadata']
+): Space => ({
+  id,
+  name,
+  userId,
+  sourceType,
+  rootPath: null,
+  rootFingerprint: null,
+  status: 'active',
+  schemaVersion: SPACE_SCHEMA_VERSION,
+  createdAt: 1,
+  updatedAt: 1,
+  metadata,
+});
+
+describe('spaceStore user scoping', () => {
+  beforeEach(async () => {
+    vi.clearAllMocks();
+    const spaceApi = await import('@/service/spaceApi');
+    vi.mocked(spaceApi.proxyFetchSpaces).mockResolvedValue([]);
+    vi.mocked(spaceApi.proxyFetchSpaceProjects).mockResolvedValue([]);
+    vi.mocked(spaceApi.proxyCreateSpace).mockResolvedValue(
+      makeSpace('space_created', 'Untitled Space', 'blank')
+    );
+    vi.mocked(spaceApi.proxyEnsureLegacySpace).mockResolvedValue(
+      makeSpace('legacy_2', 'Legacy Space', 'legacy', '2', { legacy: true })
+    );
+    authStoreMock.state = {
+      email: 'new@example.com',
+      user_id: 2,
+    };
+    useSpaceStore.setState({
+      activeSpaceId: 'space_old_blank',
+      spaces: {
+        space_old_blank: {
+          id: 'space_old_blank',
+          name: 'Untitled Space',
+          userId: '1',
+          sourceType: 'blank',
+          status: 'active',
+          schemaVersion: SPACE_SCHEMA_VERSION,
+          createdAt: 1,
+          updatedAt: 3,
+        },
+        legacy_1: {
+          id: 'legacy_1',
+          name: 'Legacy Space',
+          userId: '1',
+          sourceType: 'legacy',
+          status: 'active',
+          schemaVersion: SPACE_SCHEMA_VERSION,
+          createdAt: 1,
+          updatedAt: 2,
+          metadata: { legacy: true },
+        },
+        space_new_blank: {
+          id: 'space_new_blank',
+          name: 'Untitled Space',
+          userId: '2',
+          sourceType: 'blank',
+          status: 'active',
+          schemaVersion: SPACE_SCHEMA_VERSION,
+          createdAt: 1,
+          updatedAt: 4,
+        },
+      },
+      lastVisitedProjectBySpace: {
+        space_old_blank: 'project_old',
+        space_new_blank: 'project_new',
+      },
+      projectsBySpaceId: {
+        space_old_blank: {
+          project_old: {
+            id: 'project_old',
+            userId: '1',
+            spaceId: 'space_old_blank',
+            name: 'Old project',
+            status: 'active',
+            createdAt: 1,
+            updatedAt: 1,
+          },
+        },
+        space_new_blank: {
+          project_new: {
+            id: 'project_new',
+            userId: '2',
+            spaceId: 'space_new_blank',
+            name: 'New project',
+            status: 'active',
+            createdAt: 1,
+            updatedAt: 1,
+          },
+        },
+      },
+      projectIdIndex: {
+        project_old: 'space_old_blank',
+        project_new: 'space_new_blank',
+      },
+      projectsSyncedAt: {
+        space_old_blank: 100,
+        legacy_1: 100,
+        space_new_blank: 200,
+      },
+    });
+  });
+
+  it('removes spaces and project metadata from the previous signed-in user', () => {
+    useSpaceStore.getState().resetForUser(2);
+
+    const state = useSpaceStore.getState();
+    expect(Object.keys(state.spaces)).toEqual(['space_new_blank']);
+    expect(state.activeSpaceId).toBe('space_new_blank');
+    expect(Object.keys(state.projectsBySpaceId)).toEqual(['space_new_blank']);
+    expect(state.projectIdIndex).toEqual({ project_new: 'space_new_blank' });
+    expect(state.lastVisitedProjectBySpace).toEqual({
+      space_new_blank: 'project_new',
+    });
+    expect(state.projectsSyncedAt).toEqual({ space_new_blank: 200 });
+  });
+
+  it('hydrates new accounts with one blank space and hides empty legacy rows', async () => {
+    const spaceApi = await import('@/service/spaceApi');
+    vi.mocked(spaceApi.proxyFetchSpaces).mockResolvedValue([
+      makeSpace('legacy_2', 'Legacy Space', 'legacy', '2', { legacy: true }),
+    ]);
+    vi.mocked(spaceApi.proxyCreateSpace).mockResolvedValue(
+      makeSpace('space_new_blank', 'Untitled Space', 'blank')
+    );
+
+    await useSpaceStore.getState().hydrateFromServer(2);
+
+    const state = useSpaceStore.getState();
+    expect(spaceApi.proxyFetchSpaceProjects).toHaveBeenCalledWith('legacy_2');
+    expect(spaceApi.proxyCreateSpace).toHaveBeenCalledWith(
+      expect.objectContaining({
+        name: 'Untitled Space',
+        source_type: 'blank',
+      })
+    );
+    expect(Object.keys(state.spaces)).toEqual(['space_new_blank']);
+    expect(state.activeSpaceId).toBe('space_new_blank');
+  });
+});
diff --git a/src/store/spaceStore.ts b/src/store/spaceStore.ts
index 83143a05..09a98a19 100644
--- a/src/store/spaceStore.ts
+++ b/src/store/spaceStore.ts
@@ -19,6 +19,7 @@ import {
   type SessionNavLeadPresentation,
 } from '@/lib/sessionNavLead';
 import {
+  isLegacySpace,
   isLocalWorkspaceSpace,
   isPlaceholderProjectName,
   isPlaceholderSpaceNameStatic,
@@ -39,6 +40,8 @@ export const DEFAULT_LOCAL_USER_ID = 'local';
 const PROJECT_SYNC_TTL_MS = 5 * 60 * 1000;
 const PROJECT_PLACEHOLDER_RESYNC_MS = 10 * 1000;
 const PROJECT_DISPLAY_NAME_MAX = 80;
+const INITIAL_BLANK_SPACE_NAME = 'Untitled Space';
+const INITIAL_BLANK_SPACE_CREATED_FROM = 'initial_hydrate';
 
 export type SpaceSourceType = 'blank' | 'folder' | 'legacy';
 export type SpaceStatus = 'active' | 'disconnected' | 'archived';
@@ -102,6 +105,7 @@ interface SpaceStore {
   projectsBySpaceId: Record<string, Record<string, SpaceProjectMeta>>;
   projectIdIndex: Record<string, string>;
   projectsSyncedAt: Record<string, number>;
+  resetForUser: (userId?: string | number | null) => void;
   ensureLegacySpace: (userId?: string | number | null) => string;
   hydrateFromServer: (userId?: string | number | null) => Promise<void>;
   syncProjectsFromServer: (spaceId: string) => Promise<void>;
@@ -160,6 +164,12 @@ const canonicalUserId = (userId?: string | number | null) =>
     ? DEFAULT_LOCAL_USER_ID
     : String(userId);
 
+const spaceBelongsToUser = (space: Space, userId?: string | number | null) => {
+  const ownerId = canonicalUserId(userId);
+  if (!space.userId) return ownerId === DEFAULT_LOCAL_USER_ID;
+  return String(space.userId) === ownerId;
+};
+
 export const legacySpaceIdForUser = (userId?: string | number | null) =>
   `legacy_${canonicalUserId(userId)}`;
 
@@ -233,6 +243,7 @@ const hasVisibleProjectsForSpace = (
 ) => getVisibleProjectMetasForSpace(projectsBySpaceId, spaceId).length > 0;
 
 const DISPOSABLE_BLANK_SPACE_CREATED_FROM = new Set([
+  INITIAL_BLANK_SPACE_CREATED_FROM,
   'home_hub_toolbar',
   'top_bar',
   'project_sidebar_space_selector',
@@ -328,6 +339,40 @@ const pruneAutoCreatedProjectMetas = (
   };
 };
 
+const activeSpacesByRecentUpdate = (spaces: Record<string, Space>) =>
+  Object.values(spaces)
+    .filter((space) => space.status === 'active')
+    .sort((a, b) => b.updatedAt - a.updatedAt);
+
+const pickHydratedActiveSpaceId = (
+  spaces: Record<string, Space>,
+  currentActiveSpaceId: string | null | undefined,
+  localLegacyId: string,
+  preferredSpaceId?: string | null
+) => {
+  if (preferredSpaceId && spaces[preferredSpaceId]?.status === 'active') {
+    return preferredSpaceId;
+  }
+
+  const currentActiveSpace = currentActiveSpaceId
+    ? spaces[currentActiveSpaceId]
+    : null;
+  if (
+    currentActiveSpace &&
+    currentActiveSpace.status === 'active' &&
+    currentActiveSpace.id !== localLegacyId
+  ) {
+    return currentActiveSpace.id;
+  }
+
+  const activeSpaces = activeSpacesByRecentUpdate(spaces);
+  return (
+    activeSpaces.find((space) => !isLegacySpace(space))?.id ??
+    activeSpaces[0]?.id ??
+    null
+  );
+};
+
 const truncateProjectDisplayName = (name: string) =>
   name.length > PROJECT_DISPLAY_NAME_MAX
     ? `${name.slice(0, PROJECT_DISPLAY_NAME_MAX - 3)}...`
@@ -429,6 +474,15 @@ const unbindBrainWorkspaceMirror = async (spaceId: string) => {
   await unbindWorkspaceFromBrain(spaceId, email, userId);
 };
 
+const isHydrationStillCurrentForUser = async (ownerId: string) => {
+  try {
+    const { getAuthStore } = await import('@/store/authStore');
+    return canonicalUserId(getAuthStore().user_id) === ownerId;
+  } catch {
+    return true;
+  }
+};
+
 export const useSpaceStore = create<SpaceStore>()(
   persist(
     (set, get) => ({
@@ -439,22 +493,138 @@ export const useSpaceStore = create<SpaceStore>()(
       projectIdIndex: {},
       projectsSyncedAt: {},
 
+      resetForUser: (userId) =>
+        set((state) => {
+          const nextSpaces: Record<string, Space> = {};
+          for (const [spaceId, space] of Object.entries(state.spaces)) {
+            if (spaceBelongsToUser(space, userId)) {
+              nextSpaces[spaceId] = space;
+            }
+          }
+
+          const nextProjectsBySpaceId: Record<
+            string,
+            Record<string, SpaceProjectMeta>
+          > = {};
+          const nextProjectIdIndex: Record<string, string> = {};
+          for (const spaceId of Object.keys(nextSpaces)) {
+            const projects = state.projectsBySpaceId[spaceId];
+            if (!projects) continue;
+            nextProjectsBySpaceId[spaceId] = projects;
+            for (const projectId of Object.keys(projects)) {
+              nextProjectIdIndex[projectId] = spaceId;
+            }
+          }
+
+          const nextLastVisitedProjectBySpace: Record<string, string> = {};
+          for (const [spaceId, projectId] of Object.entries(
+            state.lastVisitedProjectBySpace
+          )) {
+            if (nextProjectsBySpaceId[spaceId]?.[projectId]) {
+              nextLastVisitedProjectBySpace[spaceId] = projectId;
+            }
+          }
+
+          const nextProjectsSyncedAt: Record<string, number> = {};
+          for (const spaceId of Object.keys(nextSpaces)) {
+            const syncedAt = state.projectsSyncedAt[spaceId];
+            if (syncedAt !== undefined) {
+              nextProjectsSyncedAt[spaceId] = syncedAt;
+            }
+          }
+
+          const localLegacyId = legacySpaceIdForUser(DEFAULT_LOCAL_USER_ID);
+          return {
+            spaces: nextSpaces,
+            activeSpaceId: pickHydratedActiveSpaceId(
+              nextSpaces,
+              state.activeSpaceId,
+              localLegacyId
+            ),
+            lastVisitedProjectBySpace: nextLastVisitedProjectBySpace,
+            projectsBySpaceId: nextProjectsBySpaceId,
+            projectIdIndex: nextProjectIdIndex,
+            projectsSyncedAt: nextProjectsSyncedAt,
+          };
+        }),
+
       hydrateFromServer: async (userId) => {
         try {
-          const [{ proxyEnsureLegacySpace, proxyFetchSpaces }, projectModule] =
-            await Promise.all([
-              import('@/service/spaceApi'),
-              import('./projectRuntimeStore'),
-            ]);
-          const [legacySpace, serverSpaces] = await Promise.all([
-            proxyEnsureLegacySpace(),
-            proxyFetchSpaces(),
+          const [
+            { proxyCreateSpace, proxyFetchSpaceProjects, proxyFetchSpaces },
+            projectModule,
+          ] = await Promise.all([
+            import('@/service/spaceApi'),
+            import('./projectRuntimeStore'),
           ]);
-          const spaces = serverSpaces.some(
-            (space) => space.id === legacySpace.id
-          )
-            ? serverSpaces
-            : [legacySpace, ...serverSpaces];
+          const ownerId = canonicalUserId(userId);
+          const serverSpaces = await proxyFetchSpaces();
+          if (!(await isHydrationStillCurrentForUser(ownerId))) {
+            return;
+          }
+          const ownedSpaces = serverSpaces.filter(
+            (space) => !space.userId || String(space.userId) === ownerId
+          );
+          const activeOwnedSpaces = ownedSpaces.filter(
+            (space) => space.status === 'active'
+          );
+          const hasActiveNonLegacySpace = activeOwnedSpaces.some(
+            (space) => !isLegacySpace(space)
+          );
+          const activeLegacySpaces = activeOwnedSpaces.filter(isLegacySpace);
+          const legacySpaceIdsWithProjects = new Set<string>();
+          let initialBlankSpace: Space | null = null;
+
+          for (const legacySpace of activeLegacySpaces) {
+            try {
+              const legacyProjects = await proxyFetchSpaceProjects(
+                legacySpace.id
+              );
+              if (
+                legacyProjects.some((project) => project.status !== 'archived')
+              ) {
+                legacySpaceIdsWithProjects.add(legacySpace.id);
+              }
+            } catch (error) {
+              console.warn(
+                `[spaceStore] Failed to inspect legacy Space ${legacySpace.id}; preserving it as the active fallback:`,
+                error
+              );
+              legacySpaceIdsWithProjects.add(legacySpace.id);
+            }
+          }
+
+          if (!hasActiveNonLegacySpace) {
+            if (legacySpaceIdsWithProjects.size === 0) {
+              try {
+                initialBlankSpace = await proxyCreateSpace({
+                  name: INITIAL_BLANK_SPACE_NAME,
+                  source_type: 'blank',
+                  metadata: {
+                    createdFrom: INITIAL_BLANK_SPACE_CREATED_FROM,
+                    autoCreatedPlaceholder: true,
+                  },
+                });
+              } catch (error) {
+                console.warn(
+                  '[spaceStore] Failed to create initial blank Space:',
+                  error
+                );
+              }
+            }
+          }
+
+          if (!(await isHydrationStillCurrentForUser(ownerId))) {
+            return;
+          }
+
+          const visibleOwnedSpaces = ownedSpaces.filter(
+            (space) =>
+              !isLegacySpace(space) || legacySpaceIdsWithProjects.has(space.id)
+          );
+          const spaces = initialBlankSpace
+            ? [initialBlankSpace, ...visibleOwnedSpaces]
+            : visibleOwnedSpaces;
           void Promise.all([
             import('@/service/workspaceApi'),
             import('@/store/authStore'),
@@ -464,7 +634,10 @@ export const useSpaceStore = create<SpaceStore>()(
               const userId = authModule.getAuthStore().user_id;
               if (!email) return;
               const bindingSpaceIds = spaces
-                .filter((space) => space.status !== 'archived')
+                .filter(
+                  (space) =>
+                    space.status !== 'archived' && !isLegacySpace(space)
+                )
                 .map((space) => space.id);
               return workspaceModule
                 .reconcileWorkspaceBindings(email, bindingSpaceIds, userId)
@@ -500,28 +673,24 @@ export const useSpaceStore = create<SpaceStore>()(
               );
             });
           const localLegacyId = legacySpaceIdForUser(DEFAULT_LOCAL_USER_ID);
-          const serverLegacyId = legacySpace.id;
-          const ownerId = canonicalUserId(userId ?? legacySpace.userId);
+          const serverLegacySpace = spaces.find(isLegacySpace);
+          const serverLegacyId =
+            serverLegacySpace?.id ?? legacySpaceIdForUser(ownerId);
+          const hasServerLegacySpace = Boolean(serverLegacySpace);
 
           set((state) => {
             const nextSpaces: Record<string, Space> = {};
             for (const space of spaces) {
-              if (!space.userId || String(space.userId) === ownerId) {
-                nextSpaces[space.id] = space;
-              }
+              nextSpaces[space.id] = space;
             }
-            if (!nextSpaces[serverLegacyId]) {
-              nextSpaces[serverLegacyId] = legacySpace;
-            }
-            const shouldAdoptServerLegacy =
-              !state.activeSpaceId ||
-              state.activeSpaceId === localLegacyId ||
-              !nextSpaces[state.activeSpaceId];
             return {
               spaces: nextSpaces,
-              activeSpaceId: shouldAdoptServerLegacy
-                ? serverLegacyId
-                : state.activeSpaceId,
+              activeSpaceId: pickHydratedActiveSpaceId(
+                nextSpaces,
+                state.activeSpaceId,
+                localLegacyId,
+                initialBlankSpace?.id
+              ),
             };
           });
 
@@ -543,11 +712,13 @@ export const useSpaceStore = create<SpaceStore>()(
               projectIdIndex: pruned.projectIdIndex,
             };
           });
-          rehomeLegacyRuntimeProjects(
-            projectStore,
-            localLegacyId,
-            serverLegacyId
-          );
+          if (hasServerLegacySpace) {
+            rehomeLegacyRuntimeProjects(
+              projectStore,
+              localLegacyId,
+              serverLegacyId
+            );
+          }
 
           const activeSpaceId = get().activeSpaceId;
           if (activeSpaceId && get().shouldSyncProjects(activeSpaceId)) {
@@ -561,7 +732,6 @@ export const useSpaceStore = create<SpaceStore>()(
             '[spaceStore] Failed to hydrate spaces from server:',
             error
           );
-          get().ensureLegacySpace(userId);
         }
       },