apps/api/src/app.module.ts

@@ -42,6 +42,7 @@ import { SpeechModule } from "./speech/speech.module";
 import { DashboardModule } from "./dashboard/dashboard.module";
 import { TerminalModule } from "./terminal/terminal.module";
 import { PersonalitiesModule } from "./personalities/personalities.module";
+import { WorkspacesModule } from "./workspaces/workspaces.module";
 import { RlsContextInterceptor } from "./common/interceptors/rls-context.interceptor";
 
 @Module({
@@ -107,6 +108,7 @@ import { RlsContextInterceptor } from "./common/interceptors/rls-context.interce
     DashboardModule,
     TerminalModule,
     PersonalitiesModule,
+    WorkspacesModule,
   ],
   controllers: [AppController, CsrfController],
   providers: [

apps/api/src/auth/auth.controller.spec.ts

@@ -361,16 +361,13 @@ describe("AuthController", () => {
   });
 
   describe("getProfile", () => {
-    it("should return complete user profile with workspace fields", () => {
+    it("should return complete user profile with identity fields", () => {
       const mockUser: AuthUser = {
         id: "user-123",
         email: "test@example.com",
         name: "Test User",
         image: "https://example.com/avatar.jpg",
         emailVerified: true,
-        workspaceId: "workspace-123",
-        currentWorkspaceId: "workspace-456",
-        workspaceRole: "admin",
       };
 
       const result = controller.getProfile(mockUser);
@@ -381,13 +378,10 @@ describe("AuthController", () => {
         name: mockUser.name,
         image: mockUser.image,
         emailVerified: mockUser.emailVerified,
-        workspaceId: mockUser.workspaceId,
-        currentWorkspaceId: mockUser.currentWorkspaceId,
-        workspaceRole: mockUser.workspaceRole,
       });
     });
 
-    it("should return user profile with optional fields undefined", () => {
+    it("should return user profile with only required fields", () => {
       const mockUser: AuthUser = {
         id: "user-123",
         email: "test@example.com",
@@ -400,12 +394,11 @@ describe("AuthController", () => {
         id: mockUser.id,
         email: mockUser.email,
         name: mockUser.name,
-        image: undefined,
-        emailVerified: undefined,
-        workspaceId: undefined,
-        currentWorkspaceId: undefined,
-        workspaceRole: undefined,
       });
+      // Workspace fields are not included — served by GET /api/workspaces
+      expect(result).not.toHaveProperty("workspaceId");
+      expect(result).not.toHaveProperty("currentWorkspaceId");
+      expect(result).not.toHaveProperty("workspaceRole");
     });
   });
 

apps/api/src/auth/auth.controller.ts

@@ -72,15 +72,10 @@ export class AuthController {
     if (user.emailVerified !== undefined) {
       profile.emailVerified = user.emailVerified;
     }
-    if (user.workspaceId !== undefined) {
+
-      profile.workspaceId = user.workspaceId;
+    // Workspace context is served by GET /api/workspaces, not the auth profile.
-    }
+    // The deprecated workspaceId/currentWorkspaceId/workspaceRole fields on
-    if (user.currentWorkspaceId !== undefined) {
+    // AuthUser are never populated by BetterAuth and are omitted here.
-      profile.currentWorkspaceId = user.currentWorkspaceId;
-    }
-    if (user.workspaceRole !== undefined) {
-      profile.workspaceRole = user.workspaceRole;
-    }
 
     return profile;
   }

apps/api/src/workspaces/dto/index.ts

@@ -0,0 +1 @@
+export { WorkspaceResponseDto } from "./workspace-response.dto";

apps/api/src/workspaces/dto/workspace-response.dto.ts

@@ -0,0 +1,12 @@
+import type { WorkspaceMemberRole } from "@prisma/client";
+
+/**
+ * Response DTO for a workspace the authenticated user belongs to.
+ */
+export class WorkspaceResponseDto {
+  id!: string;
+  name!: string;
+  ownerId!: string;
+  role!: WorkspaceMemberRole;
+  createdAt!: Date;
+}

apps/api/src/workspaces/index.ts

@@ -0,0 +1,3 @@
+export { WorkspacesModule } from "./workspaces.module";
+export { WorkspacesService } from "./workspaces.service";
+export { WorkspacesController } from "./workspaces.controller";

apps/api/src/workspaces/workspaces.controller.spec.ts

@@ -0,0 +1,75 @@
+import { describe, it, expect, beforeEach, vi } from "vitest";
+import { Test, TestingModule } from "@nestjs/testing";
+import { WorkspacesController } from "./workspaces.controller";
+import { WorkspacesService } from "./workspaces.service";
+import { AuthGuard } from "../auth/guards/auth.guard";
+import { WorkspaceMemberRole } from "@prisma/client";
+import type { AuthUser } from "@mosaic/shared";
+
+describe("WorkspacesController", () => {
+  let controller: WorkspacesController;
+  let service: WorkspacesService;
+
+  const mockWorkspacesService = {
+    getUserWorkspaces: vi.fn(),
+  };
+
+  const mockUser: AuthUser = {
+    id: "user-1",
+    email: "test@example.com",
+    name: "Test User",
+  };
+
+  beforeEach(async () => {
+    const module: TestingModule = await Test.createTestingModule({
+      controllers: [WorkspacesController],
+      providers: [
+        {
+          provide: WorkspacesService,
+          useValue: mockWorkspacesService,
+        },
+      ],
+    })
+      .overrideGuard(AuthGuard)
+      .useValue({ canActivate: () => true })
+      .compile();
+
+    controller = module.get<WorkspacesController>(WorkspacesController);
+    service = module.get<WorkspacesService>(WorkspacesService);
+
+    vi.clearAllMocks();
+  });
+
+  describe("GET /api/workspaces", () => {
+    it("should call service with authenticated user id", async () => {
+      mockWorkspacesService.getUserWorkspaces.mockResolvedValueOnce([]);
+
+      await controller.getUserWorkspaces(mockUser);
+
+      expect(service.getUserWorkspaces).toHaveBeenCalledWith("user-1");
+    });
+
+    it("should return workspace list from service", async () => {
+      const mockWorkspaces = [
+        {
+          id: "ws-1",
+          name: "My Workspace",
+          ownerId: "user-1",
+          role: WorkspaceMemberRole.OWNER,
+          createdAt: new Date("2026-01-01"),
+        },
+      ];
+      mockWorkspacesService.getUserWorkspaces.mockResolvedValueOnce(mockWorkspaces);
+
+      const result = await controller.getUserWorkspaces(mockUser);
+
+      expect(result).toEqual(mockWorkspaces);
+    });
+
+    it("should propagate service errors", async () => {
+      mockWorkspacesService.getUserWorkspaces.mockRejectedValueOnce(new Error("Database error"));
+
+      await expect(controller.getUserWorkspaces(mockUser)).rejects.toThrow("Database error");
+    });
+  });
+});

apps/api/src/workspaces/workspaces.controller.ts

@@ -0,0 +1,28 @@
+import { Controller, Get, UseGuards } from "@nestjs/common";
+import { WorkspacesService } from "./workspaces.service";
+import { AuthGuard } from "../auth/guards/auth.guard";
+import { CurrentUser } from "../auth/decorators/current-user.decorator";
+import type { AuthUser } from "@mosaic/shared";
+import type { WorkspaceResponseDto } from "./dto";
+
+/**
+ * User-scoped workspace operations.
+ *
+ * Intentionally does NOT use WorkspaceGuard — these routes operate across all
+ * workspaces the user belongs to, not within a single workspace context.
+ */
+@Controller("workspaces")
+@UseGuards(AuthGuard)
+export class WorkspacesController {
+  constructor(private readonly workspacesService: WorkspacesService) {}
+
+  /**
+   * GET /api/workspaces
+   * Returns workspaces the authenticated user is a member of.
+   * Auto-provisions a default workspace if the user has none.
+   */
+  @Get()
+  async getUserWorkspaces(@CurrentUser() user: AuthUser): Promise<WorkspaceResponseDto[]> {
+    return this.workspacesService.getUserWorkspaces(user.id);
+  }
+}

apps/api/src/workspaces/workspaces.module.ts

@@ -0,0 +1,13 @@
+import { Module } from "@nestjs/common";
+import { WorkspacesController } from "./workspaces.controller";
+import { WorkspacesService } from "./workspaces.service";
+import { PrismaModule } from "../prisma/prisma.module";
+import { AuthModule } from "../auth/auth.module";
+
+@Module({
+  imports: [PrismaModule, AuthModule],
+  controllers: [WorkspacesController],
+  providers: [WorkspacesService],
+  exports: [WorkspacesService],
+})
+export class WorkspacesModule {}

apps/api/src/workspaces/workspaces.service.spec.ts

@@ -0,0 +1,229 @@
+import { describe, it, expect, beforeEach, vi } from "vitest";
+import { Test, TestingModule } from "@nestjs/testing";
+import { WorkspacesService } from "./workspaces.service";
+import { PrismaService } from "../prisma/prisma.service";
+import { WorkspaceMemberRole } from "@prisma/client";
+
+describe("WorkspacesService", () => {
+  let service: WorkspacesService;
+
+  const mockUserId = "550e8400-e29b-41d4-a716-446655440001";
+  const mockWorkspaceId = "550e8400-e29b-41d4-a716-446655440002";
+
+  const mockWorkspace = {
+    id: mockWorkspaceId,
+    name: "Test Workspace",
+    ownerId: mockUserId,
+    settings: {},
+    matrixRoomId: null,
+    createdAt: new Date("2026-01-01"),
+    updatedAt: new Date("2026-01-01"),
+  };
+
+  const mockMembership = {
+    workspaceId: mockWorkspaceId,
+    userId: mockUserId,
+    role: WorkspaceMemberRole.OWNER,
+    joinedAt: new Date("2026-01-01"),
+    workspace: {
+      id: mockWorkspaceId,
+      name: "Test Workspace",
+      ownerId: mockUserId,
+      createdAt: new Date("2026-01-01"),
+    },
+  };
+
+  const mockPrismaService = {
+    workspaceMember: {
+      findMany: vi.fn(),
+      create: vi.fn(),
+    },
+    workspace: {
+      create: vi.fn(),
+    },
+    $transaction: vi.fn(),
+  };
+
+  beforeEach(async () => {
+    const module: TestingModule = await Test.createTestingModule({
+      providers: [
+        WorkspacesService,
+        {
+          provide: PrismaService,
+          useValue: mockPrismaService,
+        },
+      ],
+    }).compile();
+
+    service = module.get<WorkspacesService>(WorkspacesService);
+
+    vi.clearAllMocks();
+  });
+
+  describe("getUserWorkspaces", () => {
+    it("should return all workspaces user is a member of", async () => {
+      mockPrismaService.workspaceMember.findMany.mockResolvedValueOnce([mockMembership]);
+
+      const result = await service.getUserWorkspaces(mockUserId);
+
+      expect(result).toEqual([
+        {
+          id: mockWorkspaceId,
+          name: "Test Workspace",
+          ownerId: mockUserId,
+          role: WorkspaceMemberRole.OWNER,
+          createdAt: mockMembership.workspace.createdAt,
+        },
+      ]);
+      expect(mockPrismaService.workspaceMember.findMany).toHaveBeenCalledWith({
+        where: { userId: mockUserId },
+        include: {
+          workspace: {
+            select: { id: true, name: true, ownerId: true, createdAt: true },
+          },
+        },
+        orderBy: { joinedAt: "asc" },
+      });
+    });
+
+    it("should return multiple workspaces ordered by joinedAt", async () => {
+      const secondWorkspace = {
+        ...mockMembership,
+        workspaceId: "ws-2",
+        role: WorkspaceMemberRole.MEMBER,
+        joinedAt: new Date("2026-02-01"),
+        workspace: {
+          id: "ws-2",
+          name: "Second Workspace",
+          ownerId: "other-user",
+          createdAt: new Date("2026-02-01"),
+        },
+      };
+
+      mockPrismaService.workspaceMember.findMany.mockResolvedValueOnce([
+        mockMembership,
+        secondWorkspace,
+      ]);
+
+      const result = await service.getUserWorkspaces(mockUserId);
+
+      expect(result).toHaveLength(2);
+      expect(result[0].id).toBe(mockWorkspaceId);
+      expect(result[1].id).toBe("ws-2");
+      expect(result[1].role).toBe(WorkspaceMemberRole.MEMBER);
+    });
+
+    it("should auto-provision a default workspace when user has no memberships", async () => {
+      mockPrismaService.workspaceMember.findMany.mockResolvedValueOnce([]);
+      mockPrismaService.$transaction.mockImplementationOnce(
+        async (fn: (tx: typeof mockPrismaService) => Promise<unknown>) => {
+          const txMock = {
+            workspaceMember: {
+              findFirst: vi.fn().mockResolvedValueOnce(null),
+              create: vi.fn().mockResolvedValueOnce({}),
+            },
+            workspace: {
+              create: vi.fn().mockResolvedValueOnce(mockWorkspace),
+            },
+          };
+          return fn(txMock as unknown as typeof mockPrismaService);
+        }
+      );
+
+      const result = await service.getUserWorkspaces(mockUserId);
+
+      expect(result).toHaveLength(1);
+      expect(result[0].name).toBe("Test Workspace");
+      expect(result[0].role).toBe(WorkspaceMemberRole.OWNER);
+      expect(mockPrismaService.$transaction).toHaveBeenCalledTimes(1);
+    });
+
+    it("should return existing workspace if one was created between initial check and transaction", async () => {
+      // Simulates a race condition: initial findMany returns [], but inside the
+      // transaction another request already created a workspace.
+      mockPrismaService.workspaceMember.findMany.mockResolvedValueOnce([]);
+      mockPrismaService.$transaction.mockImplementationOnce(
+        async (fn: (tx: typeof mockPrismaService) => Promise<unknown>) => {
+          const txMock = {
+            workspaceMember: {
+              findFirst: vi.fn().mockResolvedValueOnce(mockMembership),
+            },
+            workspace: {
+              create: vi.fn(),
+            },
+          };
+          return fn(txMock as unknown as typeof mockPrismaService);
+        }
+      );
+
+      const result = await service.getUserWorkspaces(mockUserId);
+
+      expect(result).toHaveLength(1);
+      expect(result[0].id).toBe(mockWorkspaceId);
+      expect(result[0].name).toBe("Test Workspace");
+    });
+
+    it("should create workspace with correct data during auto-provisioning", async () => {
+      mockPrismaService.workspaceMember.findMany.mockResolvedValueOnce([]);
+
+      let capturedWorkspaceData: unknown;
+      let capturedMemberData: unknown;
+
+      mockPrismaService.$transaction.mockImplementationOnce(
+        async (fn: (tx: typeof mockPrismaService) => Promise<unknown>) => {
+          const txMock = {
+            workspaceMember: {
+              findFirst: vi.fn().mockResolvedValueOnce(null),
+              create: vi.fn().mockImplementation((args: unknown) => {
+                capturedMemberData = args;
+                return {};
+              }),
+            },
+            workspace: {
+              create: vi.fn().mockImplementation((args: unknown) => {
+                capturedWorkspaceData = args;
+                return mockWorkspace;
+              }),
+            },
+          };
+          return fn(txMock as unknown as typeof mockPrismaService);
+        }
+      );
+
+      await service.getUserWorkspaces(mockUserId);
+
+      expect(capturedWorkspaceData).toEqual({
+        data: {
+          name: "My Workspace",
+          ownerId: mockUserId,
+          settings: {},
+        },
+      });
+      expect(capturedMemberData).toEqual({
+        data: {
+          workspaceId: mockWorkspaceId,
+          userId: mockUserId,
+          role: WorkspaceMemberRole.OWNER,
+        },
+      });
+    });
+
+    it("should not auto-provision when user already has workspaces", async () => {
+      mockPrismaService.workspaceMember.findMany.mockResolvedValueOnce([mockMembership]);
+
+      await service.getUserWorkspaces(mockUserId);
+
+      expect(mockPrismaService.$transaction).not.toHaveBeenCalled();
+    });
+
+    it("should propagate database errors", async () => {
+      mockPrismaService.workspaceMember.findMany.mockRejectedValueOnce(
+        new Error("Database connection failed")
+      );
+
+      await expect(service.getUserWorkspaces(mockUserId)).rejects.toThrow(
+        "Database connection failed"
+      );
+    });
+  });
+});

apps/api/src/workspaces/workspaces.service.ts

@@ -0,0 +1,97 @@
+import { Injectable, Logger } from "@nestjs/common";
+import { WorkspaceMemberRole } from "@prisma/client";
+import { PrismaService } from "../prisma/prisma.service";
+import type { WorkspaceResponseDto } from "./dto";
+
+@Injectable()
+export class WorkspacesService {
+  private readonly logger = new Logger(WorkspacesService.name);
+
+  constructor(private readonly prisma: PrismaService) {}
+
+  /**
+   * Get all workspaces the user is a member of.
+   *
+   * Auto-provisioning: if the user has no workspace memberships (e.g. fresh
+   * signup via BetterAuth), a default workspace is created atomically and
+   * returned.  This is the only call site for workspace bootstrapping.
+   */
+  async getUserWorkspaces(userId: string): Promise<WorkspaceResponseDto[]> {
+    const memberships = await this.prisma.workspaceMember.findMany({
+      where: { userId },
+      include: {
+        workspace: {
+          select: { id: true, name: true, ownerId: true, createdAt: true },
+        },
+      },
+      orderBy: { joinedAt: "asc" },
+    });
+
+    if (memberships.length > 0) {
+      return memberships.map((m) => ({
+        id: m.workspace.id,
+        name: m.workspace.name,
+        ownerId: m.workspace.ownerId,
+        role: m.role,
+        createdAt: m.workspace.createdAt,
+      }));
+    }
+
+    // Auto-provision a default workspace for new users.
+    // Re-query inside the transaction to guard against concurrent requests
+    // both seeing zero memberships and creating duplicate workspaces.
+    this.logger.log(`Auto-provisioning default workspace for user ${userId}`);
+
+    const workspace = await this.prisma.$transaction(async (tx) => {
+      const existing = await tx.workspaceMember.findFirst({
+        where: { userId },
+        include: {
+          workspace: {
+            select: { id: true, name: true, ownerId: true, createdAt: true },
+          },
+        },
+      });
+      if (existing) {
+        return { ...existing.workspace, alreadyExisted: true as const };
+      }
+
+      const created = await tx.workspace.create({
+        data: {
+          name: "My Workspace",
+          ownerId: userId,
+          settings: {},
+        },
+      });
+      await tx.workspaceMember.create({
+        data: {
+          workspaceId: created.id,
+          userId,
+          role: WorkspaceMemberRole.OWNER,
+        },
+      });
+      return { ...created, alreadyExisted: false as const };
+    });
+
+    if (workspace.alreadyExisted) {
+      return [
+        {
+          id: workspace.id,
+          name: workspace.name,
+          ownerId: workspace.ownerId,
+          role: WorkspaceMemberRole.OWNER,
+          createdAt: workspace.createdAt,
+        },
+      ];
+    }
+
+    return [
+      {
+        id: workspace.id,
+        name: workspace.name,
+        ownerId: workspace.ownerId,
+        role: WorkspaceMemberRole.OWNER,
+        createdAt: workspace.createdAt,
+      },
+    ];
+  }
+}

apps/web/src/app/(authenticated)/profile/page.tsx

@@ -265,23 +265,8 @@ export default function ProfilePage(): ReactElement {
               </p>
             )}
 
-            {user?.workspaceRole && (
+            {/* Workspace role badge — placeholder until workspace context API
-              <span
+                provides role data via GET /api/workspaces */}
-                style={{
-                  display: "inline-block",
-                  marginTop: 8,
-                  padding: "3px 10px",
-                  borderRadius: "var(--r)",
-                  background: "rgba(47, 128, 255, 0.1)",
-                  color: "var(--ms-blue-400)",
-                  fontSize: "0.75rem",
-                  fontWeight: 600,
-                  textTransform: "capitalize",
-                }}
-              >
-                {user.workspaceRole}
-              </span>
-            )}
           </div>
         </div>
       </div>

apps/web/src/components/chat/Chat.tsx

@@ -5,6 +5,7 @@ import { useAuth } from "@/lib/auth/auth-context";
 import { useChat } from "@/hooks/useChat";
 import { useOrchestratorCommands } from "@/hooks/useOrchestratorCommands";
 import { useWebSocket } from "@/hooks/useWebSocket";
+import { useWorkspaceId } from "@/lib/hooks";
 import { MessageList } from "./MessageList";
 import { ChatInput, type ModelId, DEFAULT_TEMPERATURE, DEFAULT_MAX_TOKENS } from "./ChatInput";
 import { ChatEmptyState } from "./ChatEmptyState";
@@ -89,10 +90,10 @@ export const Chat = forwardRef<ChatRef, ChatProps>(function Chat(
     ...(initialProjectId !== undefined && { projectId: initialProjectId }),
   });
 
-  // Use the actual workspace ID for the WebSocket room subscription.
+  // Read workspace ID from localStorage (set by auth-context after session check).
   // Cookie-based auth (withCredentials) handles authentication, so no explicit
   // token is needed here — pass an empty string as the token placeholder.
-  const workspaceId = user?.currentWorkspaceId ?? user?.workspaceId ?? "";
+  const workspaceId = useWorkspaceId() ?? "";
   const { isConnected: isWsConnected } = useWebSocket(workspaceId, "", {});
 
   const { isCommand, executeCommand } = useOrchestratorCommands();

apps/web/src/components/layout/AppSidebar.tsx

@@ -464,7 +464,7 @@ function UserCard({ collapsed }: UserCardProps): React.JSX.Element {
 
   const displayName = user?.name ?? "User";
   const initials = getInitials(displayName);
-  const role = user?.workspaceRole ?? "Member";
+  const role = "Member";
 
   return (
     <footer

apps/web/src/lib/api/index.ts

@@ -15,3 +15,4 @@ export * from "./personalities";
 export * from "./telemetry";
 export * from "./dashboard";
 export * from "./projects";
+export * from "./workspaces";

apps/web/src/lib/api/workspaces.ts

@@ -0,0 +1,26 @@
+/**
+ * Workspaces API Client
+ * User-scoped workspace discovery — does NOT require X-Workspace-Id header.
+ */
+
+import { apiGet } from "./client";
+
+/**
+ * A workspace entry from the user's membership list.
+ * Matches WorkspaceResponseDto from the API.
+ */
+export interface UserWorkspace {
+  id: string;
+  name: string;
+  ownerId: string;
+  role: string;
+  createdAt: string;
+}
+
+/**
+ * Fetch all workspaces the authenticated user is a member of.
+ * The API auto-provisions a default workspace if the user has none.
+ */
+export async function fetchUserWorkspaces(): Promise<UserWorkspace[]> {
+  return apiGet<UserWorkspace[]>("/api/workspaces");
+}

apps/web/src/lib/auth/auth-context.test.tsx

@@ -10,7 +10,13 @@ vi.mock("../api/client", () => ({
   apiPost: vi.fn(),
 }));
 
+// Mock the workspaces API client
+vi.mock("../api/workspaces", () => ({
+  fetchUserWorkspaces: vi.fn(),
+}));
+
 const { apiGet, apiPost } = await import("../api/client");
+const { fetchUserWorkspaces } = await import("../api/workspaces");
 
 /** Helper: returns a date far in the future (1 hour from now) for session mocks */
 function futureExpiry(): string {
@@ -739,19 +745,26 @@ describe("AuthContext", (): void => {
       vi.restoreAllMocks();
     });
 
-    it("should persist currentWorkspaceId to localStorage after session check", async (): Promise<void> => {
+    it("should call fetchUserWorkspaces after successful session check", async (): Promise<void> => {
       const mockUser: AuthUser = {
         id: "user-1",
         email: "test@example.com",
         name: "Test User",
-        currentWorkspaceId: "ws-current-123",
-        workspaceId: "ws-default-456",
       };
 
       vi.mocked(apiGet).mockResolvedValueOnce({
         user: mockUser,
         session: { id: "session-1", token: "token123", expiresAt: futureExpiry() },
       });
+      vi.mocked(fetchUserWorkspaces).mockResolvedValueOnce([
+        {
+          id: "ws-1",
+          name: "My Workspace",
+          ownerId: "user-1",
+          role: "OWNER",
+          createdAt: "2026-01-01",
+        },
+      ]);
 
       render(
         <AuthProvider>
@@ -763,25 +776,36 @@ describe("AuthContext", (): void => {
         expect(screen.getByTestId("auth-status")).toHaveTextContent("Authenticated");
       });
 
-      // currentWorkspaceId takes priority over workspaceId
+      expect(fetchUserWorkspaces).toHaveBeenCalledTimes(1);
-      expect(localStorageMock.setItem).toHaveBeenCalledWith(
-        "mosaic-workspace-id",
-        "ws-current-123"
-      );
     });
 
-    it("should fall back to workspaceId when currentWorkspaceId is absent", async (): Promise<void> => {
+    it("should persist the first workspace ID to localStorage", async (): Promise<void> => {
       const mockUser: AuthUser = {
         id: "user-1",
         email: "test@example.com",
         name: "Test User",
-        workspaceId: "ws-default-456",
       };
 
       vi.mocked(apiGet).mockResolvedValueOnce({
         user: mockUser,
         session: { id: "session-1", token: "token123", expiresAt: futureExpiry() },
       });
+      vi.mocked(fetchUserWorkspaces).mockResolvedValueOnce([
+        {
+          id: "ws-abc-123",
+          name: "My Workspace",
+          ownerId: "user-1",
+          role: "OWNER",
+          createdAt: "2026-01-01",
+        },
+        {
+          id: "ws-def-456",
+          name: "Second Workspace",
+          ownerId: "other",
+          role: "MEMBER",
+          createdAt: "2026-02-01",
+        },
+      ]);
 
       render(
         <AuthProvider>
@@ -793,24 +817,21 @@ describe("AuthContext", (): void => {
         expect(screen.getByTestId("auth-status")).toHaveTextContent("Authenticated");
       });
 
-      expect(localStorageMock.setItem).toHaveBeenCalledWith(
+      expect(localStorageMock.setItem).toHaveBeenCalledWith("mosaic-workspace-id", "ws-abc-123");
-        "mosaic-workspace-id",
-        "ws-default-456"
-      );
     });
 
-    it("should not write to localStorage when no workspace ID is present on user", async (): Promise<void> => {
+    it("should not write localStorage when fetchUserWorkspaces returns empty array", async (): Promise<void> => {
       const mockUser: AuthUser = {
         id: "user-1",
         email: "test@example.com",
         name: "Test User",
-        // no workspaceId or currentWorkspaceId
       };
 
       vi.mocked(apiGet).mockResolvedValueOnce({
         user: mockUser,
         session: { id: "session-1", token: "token123", expiresAt: futureExpiry() },
       });
+      vi.mocked(fetchUserWorkspaces).mockResolvedValueOnce([]);
 
       render(
         <AuthProvider>
@@ -828,18 +849,53 @@ describe("AuthContext", (): void => {
       );
     });
 
-    it("should remove workspace ID from localStorage on sign-out", async (): Promise<void> => {
+    it("should handle fetchUserWorkspaces failure gracefully — auth still succeeds", async (): Promise<void> => {
       const mockUser: AuthUser = {
         id: "user-1",
         email: "test@example.com",
         name: "Test User",
-        currentWorkspaceId: "ws-current-123",
       };
 
       vi.mocked(apiGet).mockResolvedValueOnce({
         user: mockUser,
         session: { id: "session-1", token: "token123", expiresAt: futureExpiry() },
       });
+      vi.mocked(fetchUserWorkspaces).mockRejectedValueOnce(new Error("Network error"));
+
+      render(
+        <AuthProvider>
+          <TestComponent />
+        </AuthProvider>
+      );
+
+      await waitFor(() => {
+        expect(screen.getByTestId("auth-status")).toHaveTextContent("Authenticated");
+      });
+
+      // Auth succeeded despite workspace fetch failure
+      expect(screen.getByTestId("auth-error")).toHaveTextContent("none");
+    });
+
+    it("should remove workspace ID from localStorage on sign-out", async (): Promise<void> => {
+      const mockUser: AuthUser = {
+        id: "user-1",
+        email: "test@example.com",
+        name: "Test User",
+      };
+
+      vi.mocked(apiGet).mockResolvedValueOnce({
+        user: mockUser,
+        session: { id: "session-1", token: "token123", expiresAt: futureExpiry() },
+      });
+      vi.mocked(fetchUserWorkspaces).mockResolvedValueOnce([
+        {
+          id: "ws-1",
+          name: "My Workspace",
+          ownerId: "user-1",
+          role: "OWNER",
+          createdAt: "2026-01-01",
+        },
+      ]);
       vi.mocked(apiPost).mockResolvedValueOnce({ success: true });
 
       render(

apps/web/src/lib/auth/auth-context.tsx

@@ -11,6 +11,7 @@ import {
 } from "react";
 import type { AuthUser, AuthSession } from "@mosaic/shared";
 import { apiGet, apiPost } from "../api/client";
+import { fetchUserWorkspaces } from "../api/workspaces";
 import { IS_MOCK_AUTH_MODE } from "../config";
 import { parseAuthError } from "./auth-errors";
 
@@ -134,10 +135,18 @@ function RealAuthProvider({ children }: { children: ReactNode }): React.JSX.Elem
       setUser(session.user);
       setAuthError(null);
 
-      // Persist workspace ID to localStorage so useWorkspaceId and apiRequest
+      // Fetch the user's workspace memberships and persist the default.
-      // can pick it up without re-fetching the session.
+      // Workspace context is an application concern, not an auth concern —
-      // Prefer currentWorkspaceId (the user's active workspace) over workspaceId.
+      // BetterAuth does not return workspace fields on the session user.
-      persistWorkspaceId(session.user.currentWorkspaceId ?? session.user.workspaceId);
+      try {
+        const workspaces = await fetchUserWorkspaces();
+        const defaultWorkspace = workspaces[0];
+        if (defaultWorkspace) {
+          persistWorkspaceId(defaultWorkspace.id);
+        }
+      } catch (wsError) {
+        logAuthError("Failed to fetch workspaces after session check", wsError);
+      }
 
       // Track session expiry timestamp
       expiresAtRef.current = new Date(session.session.expiresAt);

package.json

@@ -72,7 +72,8 @@
       "qs": ">=6.15.0",
       "tough-cookie": ">=4.1.3",
       "undici": ">=6.23.0",
-      "rollup": ">=4.59.0"
+      "rollup": ">=4.59.0",
+      "serialize-javascript": ">=7.0.3"
     }
   }
 }

packages/shared/src/types/auth.types.ts

@@ -13,9 +13,14 @@ export interface AuthUser {
   name: string;
   image?: string;
   emailVerified?: boolean;
-  // Workspace context (added for workspace-scoped operations)
+  /**
+   * @deprecated Never populated by BetterAuth session. Workspace context is
+   * fetched separately via GET /api/workspaces. Will be removed in a future pass.
+   */
   workspaceId?: string;
+  /** @deprecated See workspaceId. */
   currentWorkspaceId?: string;
+  /** @deprecated See workspaceId. */
   workspaceRole?: string;
 }
 

pnpm-lock.yaml

@@ -16,6 +16,7 @@ overrides:
   tough-cookie: '>=4.1.3'
   undici: '>=6.23.0'
   rollup: '>=4.59.0'
+  serialize-javascript: '>=7.0.3'
 
 importers:
 
@@ -6389,9 +6390,6 @@ packages:
   raf-schd@4.0.3:
     resolution: {integrity: sha512-tQkJl2GRWh83ui2DiPTJz9wEiMN20syf+5oKfB03yYP7ioZcJwsIK8FjrtLwH1m7C7e+Tt2yYBlrOpdT+dyeIQ==}
 
-  randombytes@2.1.0:
-    resolution: {integrity: sha512-vYl3iOX+4CKUWuxGi9Ukhie6fsqXqS9FE2Zaic4tNFD2N2QQaXOMFbuKK4QmDHC0JO6B1Zp41J0LpT0oR68amQ==}
-
   range-parser@1.2.1:
     resolution: {integrity: sha512-Hrgsx+orqoygnmhFbKaHE6c296J+HTAQXoxEF6gNupROmmGJRoyzfG3ccAveqCBrwr/2yxQ5BVd/GTl5agOwSg==}
     engines: {node: '>= 0.6'}
@@ -6679,8 +6677,9 @@ packages:
     resolution: {integrity: sha512-1gnZf7DFcoIcajTjTwjwuDjzuz4PPcY2StKPlsGAQ1+YH20IRVrBaXSWmdjowTJ6u8Rc01PoYOGHXfP1mYcZNQ==}
     engines: {node: '>= 18'}
 
-  serialize-javascript@6.0.2:
+  serialize-javascript@7.0.3:
-    resolution: {integrity: sha512-Saa1xPByTTq2gdeFZYLLo+RFE35NHZkAbqZeWNd3BpzppeVisAqpDjcp8dyf6uIvEqJRd46jemmyA4iFIeVk8g==}
+    resolution: {integrity: sha512-h+cZ/XXarqDgCjo+YSyQU/ulDEESGGf8AMK9pPNmhNSl/FzPl6L8pMp1leca5z6NuG6tvV/auC8/43tmovowww==}
+    engines: {node: '>=20.0.0'}
 
   serve-static@1.16.3:
     resolution: {integrity: sha512-x0RTqQel6g5SY7Lg6ZreMmsOzncHFU7nhnRWkKgWuMTu5NN0DR5oruckMqRvacAN9d5w6ARnRBXl9xhDCgfMeA==}
@@ -13990,10 +13989,6 @@ snapshots:
 
   raf-schd@4.0.3: {}
 
-  randombytes@2.1.0:
-    dependencies:
-      safe-buffer: 5.2.1
-
   range-parser@1.2.1: {}
 
   raw-body@2.5.3:
@@ -14362,9 +14357,7 @@ snapshots:
     transitivePeerDependencies:
       - supports-color
 
-  serialize-javascript@6.0.2:
+  serialize-javascript@7.0.3: {}
-    dependencies:
-      randombytes: 2.1.0
 
   serve-static@1.16.3:
     dependencies:
@@ -14769,7 +14762,7 @@ snapshots:
       '@jridgewell/trace-mapping': 0.3.31
       jest-worker: 27.5.1
       schema-utils: 4.3.3
-      serialize-javascript: 6.0.2
+      serialize-javascript: 7.0.3
       terser: 5.46.0
       webpack: 5.104.1(@swc/core@1.15.11)
     optionalDependencies: