diff --git a/app/routes/workspaces.py b/app/routes/workspaces.py
index 8f3d974..d921bfc 100644
--- a/app/routes/workspaces.py
+++ b/app/routes/workspaces.py
@@ -228,6 +228,9 @@ async def assign_user(
         target_uid = uuid.UUID(body.user_id)
     except ValueError:
         raise HTTPException(400, detail={"detail": "Invalid ID", "code": "invalid_id"})
+    # Cross-tenant validation: target user must belong to same tenant
+    if not await workspace_service.verify_user_same_tenant(db, tenant_id, target_uid):
+        raise HTTPException(403, detail={"detail": "Cannot assign user from different tenant", "code": "cross_tenant"})
     return await workspace_service.assign_user(db, tenant_id, wid, target_uid, body.role, assigned_by=user_id)
 
 
@@ -248,3 +251,120 @@ async def remove_user(
     removed = await workspace_service.remove_user(db, tenant_id, wid, uid)
     if not removed:
         raise HTTPException(404, detail={"detail": "User not assigned to this workspace", "code": "not_found"})
+
+
+# ─── Widget CRUD ─────────────────────────────────────────────
+
+class WidgetCreate(BaseModel):
+    widget_key: str
+    position_x: int = 0
+    position_y: int = 0
+    width: int = 1
+    height: int = 1
+    config: dict[str, Any] = {}
+
+
+class WidgetUpdate(BaseModel):
+    position_x: int | None = None
+    position_y: int | None = None
+    width: int | None = None
+    height: int | None = None
+    config: dict[str, Any] | None = None
+
+
+@router.get("/{workspace_id}/widgets")
+async def list_widgets(
+    workspace_id: str,
+    db: AsyncSession = Depends(get_db),
+    current_user: dict = Depends(require_permission("workspaces:read")),
+):
+    """List all widgets for a workspace."""
+    tenant_id = uuid.UUID(current_user["tenant_id"])
+    try:
+        wid = uuid.UUID(workspace_id)
+    except ValueError:
+        raise HTTPException(400, detail={"detail": "Invalid workspace_id", "code": "invalid_id"})
+    return {"items": await workspace_service.get_widgets(db, tenant_id, wid), "total": 0}
+
+
+@router.post("/{workspace_id}/widgets", status_code=status.HTTP_201_CREATED)
+async def create_widget(
+    workspace_id: str,
+    body: WidgetCreate,
+    db: AsyncSession = Depends(get_db),
+    current_user: dict = Depends(require_permission("workspaces:configure_modules")),
+):
+    """Create a widget in a workspace. Multiple instances of the same widget_key allowed."""
+    tenant_id = uuid.UUID(current_user["tenant_id"])
+    try:
+        wid = uuid.UUID(workspace_id)
+    except ValueError:
+        raise HTTPException(400, detail={"detail": "Invalid workspace_id", "code": "invalid_id"})
+    return await workspace_service.create_widget(
+        db, tenant_id, wid, body.widget_key,
+        body.position_x, body.position_y, body.width, body.height, body.config,
+    )
+
+
+@router.put("/{workspace_id}/widgets/{widget_id}")
+async def update_widget(
+    workspace_id: str,
+    widget_id: str,
+    body: WidgetUpdate,
+    db: AsyncSession = Depends(get_db),
+    current_user: dict = Depends(require_permission("workspaces:configure_modules")),
+):
+    """Update a widget."""
+    tenant_id = uuid.UUID(current_user["tenant_id"])
+    try:
+        wid = uuid.UUID(widget_id)
+    except ValueError:
+        raise HTTPException(400, detail={"detail": "Invalid widget_id", "code": "invalid_id"})
+    result = await workspace_service.update_widget(
+        db, tenant_id, wid,
+        body.position_x, body.position_y, body.width, body.height, body.config,
+    )
+    if result is None:
+        raise HTTPException(404, detail={"detail": "Widget not found", "code": "not_found"})
+    return result
+
+
+@router.delete("/{workspace_id}/widgets/{widget_id}", status_code=status.HTTP_204_NO_CONTENT)
+async def delete_widget(
+    workspace_id: str,
+    widget_id: str,
+    db: AsyncSession = Depends(get_db),
+    current_user: dict = Depends(require_permission("workspaces:configure_modules")),
+):
+    """Delete a widget."""
+    tenant_id = uuid.UUID(current_user["tenant_id"])
+    try:
+        wid = uuid.UUID(widget_id)
+    except ValueError:
+        raise HTTPException(400, detail={"detail": "Invalid widget_id", "code": "invalid_id"})
+    deleted = await workspace_service.delete_widget(db, tenant_id, wid)
+    if not deleted:
+        raise HTTPException(404, detail={"detail": "Widget not found", "code": "not_found"})
+
+
+# ─── Set User Default Workspace ───────────────────────────────
+
+@router.post("/{workspace_id}/set-default", status_code=status.HTTP_200_OK)
+async def set_default_workspace(
+    workspace_id: str,
+    db: AsyncSession = Depends(get_db),
+    current_user: dict = Depends(require_permission("workspaces:read")),
+):
+    """Set a workspace as the current user's default."""
+    tenant_id = uuid.UUID(current_user["tenant_id"])
+    user_id = uuid.UUID(current_user["user_id"])
+    try:
+        wid = uuid.UUID(workspace_id)
+    except ValueError:
+        raise HTTPException(400, detail={"detail": "Invalid workspace_id", "code": "invalid_id"})
+    # Verify user is assigned to this workspace
+    ctx = await workspace_service.get_workspace_context(db, tenant_id, user_id, wid)
+    if ctx is None and not current_user.get("is_system_admin"):
+        raise HTTPException(403, detail={"detail": "Not assigned to this workspace", "code": "not_assigned"})
+    await workspace_service.set_user_default_workspace(db, tenant_id, user_id, wid)
+    return {"status": "ok", "workspace_id": workspace_id}
diff --git a/app/services/workspace_service.py b/app/services/workspace_service.py
index 1478bdf..85b36c8 100644
--- a/app/services/workspace_service.py
+++ b/app/services/workspace_service.py
@@ -14,6 +14,7 @@ from sqlalchemy.ext.asyncio import AsyncSession
 from sqlalchemy.orm import selectinload
 
 from app.models.workspace import Workspace, WorkspaceModule, WorkspaceUser, WorkspaceWidget
+from app.models.user import User, UserTenant
 
 
 def _workspace_to_dict(ws: Workspace, modules: list[WorkspaceModule] | None = None, user_count: int = 0) -> dict[str, Any]:
@@ -108,6 +109,17 @@ async def create_workspace(
     is_default: bool = False,
 ) -> dict[str, Any]:
     """Create a new workspace."""
+    # If this is the default workspace, unset others FIRST (avoids unique constraint violation)
+    if is_default:
+        await db.execute(
+            update(Workspace)
+            .where(
+                Workspace.tenant_id == tenant_id,
+            )
+            .values(is_default=False)
+        )
+        await db.flush()
+
     ws = Workspace(
         tenant_id=tenant_id,
         name=name,
@@ -121,17 +133,6 @@ async def create_workspace(
     await db.flush()
     await db.refresh(ws)
     
-    # If this is the default workspace, unset others
-    if is_default:
-        await db.execute(
-            update(Workspace)
-            .where(
-                Workspace.tenant_id == tenant_id,
-                Workspace.id != ws.id,
-            )
-            .values(is_default=False)
-        )
-    
     # Auto-assign creator as manager
     wu = WorkspaceUser(
         tenant_id=tenant_id,
@@ -424,3 +425,240 @@ async def get_workspace_context(
             for w in widgets
         ],
     }
+
+# ─── Widget CRUD ─────────────────────────────────────────────
+
+async def get_widgets(
+    db: AsyncSession, tenant_id: uuid.UUID, workspace_id: uuid.UUID
+) -> list[dict[str, Any]]:
+    """List all widgets for a workspace."""
+    q = select(WorkspaceWidget).where(
+        WorkspaceWidget.workspace_id == workspace_id,
+        WorkspaceWidget.tenant_id == tenant_id,
+    ).order_by(WorkspaceWidget.position_y, WorkspaceWidget.position_x)
+    result = await db.execute(q)
+    widgets = result.scalars().all()
+    return [
+        {
+            "id": str(w.id),
+            "workspace_id": str(w.workspace_id),
+            "widget_key": w.widget_key,
+            "position_x": w.position_x,
+            "position_y": w.position_y,
+            "width": w.width,
+            "height": w.height,
+            "config": w.config or {},
+        }
+        for w in widgets
+    ]
+
+
+async def create_widget(
+    db: AsyncSession, tenant_id: uuid.UUID, workspace_id: uuid.UUID,
+    widget_key: str, position_x: int = 0, position_y: int = 0,
+    width: int = 1, height: int = 1, config: dict | None = None,
+) -> dict[str, Any]:
+    """Create a new widget in a workspace. Multiple instances of the same widget_key allowed."""
+    w = WorkspaceWidget(
+        tenant_id=tenant_id,
+        workspace_id=workspace_id,
+        widget_key=widget_key,
+        position_x=position_x,
+        position_y=position_y,
+        width=width,
+        height=height,
+        config=config or {},
+    )
+    db.add(w)
+    await db.flush()
+    await db.refresh(w)
+    return {
+        "id": str(w.id),
+        "workspace_id": str(w.workspace_id),
+        "widget_key": w.widget_key,
+        "position_x": w.position_x,
+        "position_y": w.position_y,
+        "width": w.width,
+        "height": w.height,
+        "config": w.config or {},
+    }
+
+
+async def update_widget(
+    db: AsyncSession, tenant_id: uuid.UUID, widget_id: uuid.UUID,
+    position_x: int | None = None, position_y: int | None = None,
+    width: int | None = None, height: int | None = None,
+    config: dict | None = None,
+) -> dict[str, Any] | None:
+    """Update a widget."""
+    q = select(WorkspaceWidget).where(
+        WorkspaceWidget.id == widget_id,
+        WorkspaceWidget.tenant_id == tenant_id,
+    )
+    result = await db.execute(q)
+    w = result.scalar_one_or_none()
+    if w is None:
+        return None
+    if position_x is not None:
+        w.position_x = position_x
+    if position_y is not None:
+        w.position_y = position_y
+    if width is not None:
+        w.width = width
+    if height is not None:
+        w.height = height
+    if config is not None:
+        w.config = config
+    await db.flush()
+    await db.refresh(w)
+    return {
+        "id": str(w.id),
+        "workspace_id": str(w.workspace_id),
+        "widget_key": w.widget_key,
+        "position_x": w.position_x,
+        "position_y": w.position_y,
+        "width": w.width,
+        "height": w.height,
+        "config": w.config or {},
+    }
+
+
+async def delete_widget(
+    db: AsyncSession, tenant_id: uuid.UUID, widget_id: uuid.UUID
+) -> bool:
+    """Delete a widget."""
+    q = select(WorkspaceWidget).where(
+        WorkspaceWidget.id == widget_id,
+        WorkspaceWidget.tenant_id == tenant_id,
+    )
+    result = await db.execute(q)
+    w = result.scalar_one_or_none()
+    if w is None:
+        return False
+    await db.delete(w)
+    await db.flush()
+    return True
+
+
+# ─── Manager Role Check ───────────────────────────────────────
+
+async def is_workspace_manager(
+    db: AsyncSession, tenant_id: uuid.UUID, workspace_id: uuid.UUID, user_id: uuid.UUID
+) -> bool:
+    """Check if a user is a manager of a workspace (or system admin)."""
+    q = select(WorkspaceUser).where(
+        WorkspaceUser.workspace_id == workspace_id,
+        WorkspaceUser.user_id == user_id,
+        WorkspaceUser.tenant_id == tenant_id,
+        WorkspaceUser.role == "manager",
+    )
+    result = await db.execute(q)
+    return result.scalar_one_or_none() is not None
+
+
+# ─── Cross-Tenant Validation ──────────────────────────────────
+
+async def verify_user_same_tenant(
+    db: AsyncSession, tenant_id: uuid.UUID, user_id: uuid.UUID
+) -> bool:
+    """Verify that a user belongs to the same tenant. Prevents cross-tenant assignment."""
+    q = select(UserTenant).where(
+        UserTenant.user_id == user_id,
+        UserTenant.tenant_id == tenant_id,
+    )
+    result = await db.execute(q)
+    return result.scalar_one_or_none() is not None
+
+
+# ─── Default Workspace Seeding ────────────────────────────────
+
+async def seed_default_workspace(
+    db: AsyncSession, tenant_id: uuid.UUID, user_id: uuid.UUID
+) -> dict[str, Any] | None:
+    """Create a default workspace for a tenant if none exists.
+    Called during tenant setup or user creation.
+    """
+    # Check if any workspace exists for this tenant
+    existing_q = select(Workspace).where(
+        Workspace.tenant_id == tenant_id,
+        Workspace.is_active == True,  # noqa: E712
+    )
+    result = await db.execute(existing_q)
+    if result.scalars().first() is not None:
+        return None  # Already has workspaces
+
+    # Create default workspace with all standard modules visible
+    ws = Workspace(
+        tenant_id=tenant_id,
+        name="Standard",
+        icon="LayoutGrid",
+        description="Standard-Workspace mit allen Modulen",
+        is_default=True,
+        is_active=True,
+        created_by=user_id,
+    )
+    db.add(ws)
+    await db.flush()
+    await db.refresh(ws)
+
+    # Auto-assign creator as manager
+    wu = WorkspaceUser(
+        tenant_id=tenant_id,
+        workspace_id=ws.id,
+        user_id=user_id,
+        role="manager",
+        is_default=True,
+        assigned_by=user_id,
+    )
+    db.add(wu)
+
+    # Add all standard modules visible by default
+    standard_modules = [
+        ("dashboard", 0), ("contacts", 10), ("calendar", 20),
+        ("mail", 30), ("tasks", 40), ("dms", 50),
+        ("kommunikation", 60), ("reports", 70), ("automation", 80),
+        ("tags", 90), ("settings", 100), ("audit", 110),
+    ]
+    for key, order in standard_modules:
+        wm = WorkspaceModule(
+            tenant_id=tenant_id,
+            workspace_id=ws.id,
+            module_key=key,
+            is_visible=True,
+            menu_order=order,
+            config={},
+        )
+        db.add(wm)
+
+    await db.flush()
+    return _workspace_to_dict(ws, user_count=1)
+
+
+# ─── Set User Default Workspace ───────────────────────────────
+
+async def set_user_default_workspace(
+    db: AsyncSession, tenant_id: uuid.UUID, user_id: uuid.UUID, workspace_id: uuid.UUID
+) -> bool:
+    """Set a workspace as the user's default. Unsets previous default."""
+    # Unset previous default
+    await db.execute(
+        update(WorkspaceUser)
+        .where(
+            WorkspaceUser.user_id == user_id,
+            WorkspaceUser.tenant_id == tenant_id,
+            WorkspaceUser.workspace_id != workspace_id,
+        )
+        .values(is_default=False)
+    )
+    # Set new default
+    await db.execute(
+        update(WorkspaceUser)
+        .where(
+            WorkspaceUser.user_id == user_id,
+            WorkspaceUser.tenant_id == tenant_id,
+            WorkspaceUser.workspace_id == workspace_id,
+        )
+        .values(is_default=True)
+    )
+    await db.flush()
+    return True
diff --git a/frontend/package-lock.json b/frontend/package-lock.json
index e8d3c33..be16d9e 100644
--- a/frontend/package-lock.json
+++ b/frontend/package-lock.json
@@ -46,6 +46,7 @@
       },
       "devDependencies": {
         "@playwright/test": "^1.48.0",
+        "@testing-library/dom": "^10.4.1",
         "@testing-library/jest-dom": "^6.5.0",
         "@testing-library/react": "^16.0.1",
         "@testing-library/user-event": "^14.5.2",
@@ -3172,6 +3173,25 @@
         "url": "https://github.com/sponsors/tannerlinsley"
       }
     },
+    "node_modules/@testing-library/dom": {
+      "version": "10.4.1",
+      "resolved": "https://registry.npmjs.org/@testing-library/dom/-/dom-10.4.1.tgz",
+      "integrity": "sha512-o4PXJQidqJl82ckFaXUeoAW+XysPLauYI43Abki5hABd853iMhitooc6znOnczgbTYmEP6U6/y1ZyKAIsvMKGg==",
+      "dev": true,
+      "dependencies": {
+        "@babel/code-frame": "^7.10.4",
+        "@babel/runtime": "^7.12.5",
+        "@types/aria-query": "^5.0.1",
+        "aria-query": "5.3.0",
+        "dom-accessibility-api": "^0.5.9",
+        "lz-string": "^1.5.0",
+        "picocolors": "1.1.1",
+        "pretty-format": "^27.0.2"
+      },
+      "engines": {
+        "node": ">=18"
+      }
+    },
     "node_modules/@testing-library/jest-dom": {
       "version": "6.9.1",
       "resolved": "https://registry.npmjs.org/@testing-library/jest-dom/-/jest-dom-6.9.1.tgz",
@@ -3724,6 +3744,12 @@
         "tslib": "^2.4.0"
       }
     },
+    "node_modules/@types/aria-query": {
+      "version": "5.0.4",
+      "resolved": "https://registry.npmjs.org/@types/aria-query/-/aria-query-5.0.4.tgz",
+      "integrity": "sha512-rfT93uj5s0PRL7EzccGMs3brplhcrghnDoV26NqKhCAS1hVo+WdNsPvE/yb6ilfr5hi2MEk6d5EWJTKdxg8jVw==",
+      "dev": true
+    },
     "node_modules/@types/babel__core": {
       "version": "7.20.5",
       "resolved": "https://registry.npmjs.org/@types/babel__core/-/babel__core-7.20.5.tgz",
@@ -4088,6 +4114,18 @@
         "node": ">=8"
       }
     },
+    "node_modules/ansi-styles": {
+      "version": "5.2.0",
+      "resolved": "https://registry.npmjs.org/ansi-styles/-/ansi-styles-5.2.0.tgz",
+      "integrity": "sha512-Cxwpt2SfTzTtXcfOlzGEee8O+c+MmUgGrNiBcXnuWxuFJHe6a5Hz7qwhwe5OgaSYI0IJvkLqWX1ASG+cJOkEiA==",
+      "dev": true,
+      "engines": {
+        "node": ">=10"
+      },
+      "funding": {
+        "url": "https://github.com/chalk/ansi-styles?sponsor=1"
+      }
+    },
     "node_modules/any-promise": {
       "version": "1.3.0",
       "resolved": "https://registry.npmjs.org/any-promise/-/any-promise-1.3.0.tgz",
@@ -5046,6 +5084,12 @@
       "integrity": "sha512-+HlytyjlPKnIG8XuRG8WvmBP8xs8P71y+SKKS6ZXWoEgLuePxtDoUEiH7WkdePWrQ5JBpE6aoVqfZfJUQkjXwA==",
       "dev": true
     },
+    "node_modules/dom-accessibility-api": {
+      "version": "0.5.16",
+      "resolved": "https://registry.npmjs.org/dom-accessibility-api/-/dom-accessibility-api-0.5.16.tgz",
+      "integrity": "sha512-X7BJ2yElsnOJ30pZF4uIIDfBEVgF4XEBxL9Bxhy6dnrm5hkzqmsWHGTiHqRiITNhMyFLyAiWndIJP7Z1NTteDg==",
+      "dev": true
+    },
     "node_modules/dompurify": {
       "version": "3.4.12",
       "resolved": "https://registry.npmjs.org/dompurify/-/dompurify-3.4.12.tgz",
@@ -7112,6 +7156,15 @@
         "react": "^16.5.1 || ^17.0.0 || ^18.0.0 || ^19.0.0"
       }
     },
+    "node_modules/lz-string": {
+      "version": "1.5.0",
+      "resolved": "https://registry.npmjs.org/lz-string/-/lz-string-1.5.0.tgz",
+      "integrity": "sha512-h5bgJWpxJNswbU7qCrV0tIKQCaS3blPDrqKWx+QxzuzL1zGUzij9XCWLrSLsJPu5t+eWA/ycetzYAO5IOMcWAQ==",
+      "dev": true,
+      "bin": {
+        "lz-string": "bin/bin.js"
+      }
+    },
     "node_modules/magic-string": {
       "version": "0.30.21",
       "resolved": "https://registry.npmjs.org/magic-string/-/magic-string-0.30.21.tgz",
@@ -8529,6 +8582,20 @@
         "url": "https://github.com/sponsors/sindresorhus"
       }
     },
+    "node_modules/pretty-format": {
+      "version": "27.5.1",
+      "resolved": "https://registry.npmjs.org/pretty-format/-/pretty-format-27.5.1.tgz",
+      "integrity": "sha512-Qb1gy5OrP5+zDf2Bvnzdl3jsTf1qXVMazbvCoKhtKqVs4/YK4ozX4gKQJJVyNe+cajNPn0KoC0MC3FUmaHWEmQ==",
+      "dev": true,
+      "dependencies": {
+        "ansi-regex": "^5.0.1",
+        "ansi-styles": "^5.0.0",
+        "react-is": "^17.0.1"
+      },
+      "engines": {
+        "node": "^10.13.0 || ^12.13.0 || ^14.15.0 || >=15.0.0"
+      }
+    },
     "node_modules/property-information": {
       "version": "7.2.0",
       "resolved": "https://registry.npmjs.org/property-information/-/property-information-7.2.0.tgz",
@@ -8764,6 +8831,12 @@
         }
       }
     },
+    "node_modules/react-is": {
+      "version": "17.0.2",
+      "resolved": "https://registry.npmjs.org/react-is/-/react-is-17.0.2.tgz",
+      "integrity": "sha512-w2GsyukL62IJnlaff/nRegPQR94C/XXamvMWmSHRJ4y7Ts/4ocGRmTHvOs8PSE6pB3dWOrD/nueuU5sduBsQ4w==",
+      "dev": true
+    },
     "node_modules/react-markdown": {
       "version": "10.1.0",
       "resolved": "https://registry.npmjs.org/react-markdown/-/react-markdown-10.1.0.tgz",
diff --git a/frontend/package.json b/frontend/package.json
index 98670a0..f2b781b 100644
--- a/frontend/package.json
+++ b/frontend/package.json
@@ -53,6 +53,7 @@
   },
   "devDependencies": {
     "@playwright/test": "^1.48.0",
+    "@testing-library/dom": "^10.4.1",
     "@testing-library/jest-dom": "^6.5.0",
     "@testing-library/react": "^16.0.1",
     "@testing-library/user-event": "^14.5.2",
diff --git a/frontend/src/api/client.ts b/frontend/src/api/client.ts
index 157ebd3..e8e59b8 100644
--- a/frontend/src/api/client.ts
+++ b/frontend/src/api/client.ts
@@ -30,6 +30,13 @@ export function getCsrfToken(): string | null {
 let onUnauthorized: (() => void) | null = null;
 let onValidationError: ((errors: Record<string, string[]>) => void) | null = null;
 
+ // Workspace context — set by workspaceStore, sent as X-Workspace-ID header
+ let activeWorkspaceId: string | null = null;
+
+ export function setActiveWorkspaceId(id: string | null) {
+   activeWorkspaceId = id;
+ }
+
 export function setUnauthorizedHandler(handler: () => void) {
   onUnauthorized = handler;
 }
@@ -45,6 +52,10 @@ apiClient.interceptors.request.use(
     if (unsafe.includes(config.method?.toLowerCase() ?? '') && csrfToken) {
       config.headers['X-CSRF-Token'] = csrfToken;
     }
+    // Attach X-Workspace-ID header for workspace context (per-tab)
+    if (activeWorkspaceId) {
+      config.headers['X-Workspace-ID'] = activeWorkspaceId;
+    }
     return config;
   },
   (error) => Promise.reject(error)
diff --git a/frontend/src/api/hooks/workspaces.ts b/frontend/src/api/hooks/workspaces.ts
index 70339cc..3bedc17 100644
--- a/frontend/src/api/hooks/workspaces.ts
+++ b/frontend/src/api/hooks/workspaces.ts
@@ -132,3 +132,87 @@ export function useRemoveWorkspaceUser() {
     },
   });
 }
+
+// ─── Widget Hooks ─────────────────────────────────────────────
+
+export interface WorkspaceWidget {
+  id: string;
+  workspace_id: string;
+  widget_key: string;
+  position_x: number;
+  position_y: number;
+  width: number;
+  height: number;
+  config: Record<string, any>;
+}
+
+export function useWorkspaceWidgets(workspaceId: string | null) {
+  return useQuery<{ items: WorkspaceWidget[]; total: number }>({
+    queryKey: ['workspace-widgets', workspaceId],
+    queryFn: () => apiGet(`/api/v1/workspaces/${workspaceId}/widgets`),
+    enabled: !!workspaceId,
+  });
+}
+
+export function useCreateWorkspaceWidget() {
+  const qc = useQueryClient();
+  return useMutation({
+    mutationFn: ({ workspaceId, ...data }: {
+      workspaceId: string;
+      widget_key: string;
+      position_x?: number;
+      position_y?: number;
+      width?: number;
+      height?: number;
+      config?: Record<string, any>;
+    }) => apiPost(`/api/v1/workspaces/${workspaceId}/widgets`, data),
+    onSuccess: () => {
+      qc.invalidateQueries({ queryKey: ['workspace-widgets'] });
+      qc.invalidateQueries({ queryKey: ['workspace-context'] });
+    },
+  });
+}
+
+export function useUpdateWorkspaceWidget() {
+  const qc = useQueryClient();
+  return useMutation({
+    mutationFn: ({ workspaceId, widgetId, ...data }: {
+      workspaceId: string;
+      widgetId: string;
+      position_x?: number;
+      position_y?: number;
+      width?: number;
+      height?: number;
+      config?: Record<string, any>;
+    }) => apiPut(`/api/v1/workspaces/${workspaceId}/widgets/${widgetId}`, data),
+    onSuccess: () => {
+      qc.invalidateQueries({ queryKey: ['workspace-widgets'] });
+      qc.invalidateQueries({ queryKey: ['workspace-context'] });
+    },
+  });
+}
+
+export function useDeleteWorkspaceWidget() {
+  const qc = useQueryClient();
+  return useMutation({
+    mutationFn: ({ workspaceId, widgetId }: { workspaceId: string; widgetId: string }) =>
+      apiDelete(`/api/v1/workspaces/${workspaceId}/widgets/${widgetId}`),
+    onSuccess: () => {
+      qc.invalidateQueries({ queryKey: ['workspace-widgets'] });
+      qc.invalidateQueries({ queryKey: ['workspace-context'] });
+    },
+  });
+}
+
+// ─── Set Default Workspace ────────────────────────────────────
+
+export function useSetDefaultWorkspace() {
+  const qc = useQueryClient();
+  return useMutation({
+    mutationFn: (workspaceId: string) =>
+      apiPost(`/api/v1/workspaces/${workspaceId}/set-default`),
+    onSuccess: () => {
+      qc.invalidateQueries({ queryKey: ['my-workspaces'] });
+    },
+  });
+}
diff --git a/frontend/src/hooks/useWorkspace.ts b/frontend/src/hooks/useWorkspace.ts
index 361d802..9907f3e 100644
--- a/frontend/src/hooks/useWorkspace.ts
+++ b/frontend/src/hooks/useWorkspace.ts
@@ -1,70 +1,76 @@
-import { useState, useEffect, useCallback } from 'react';
-import { useMyWorkspaces, useWorkspaceContext, type WorkspaceContext } from '@/api/hooks/workspaces';
+import { useEffect, useCallback } from 'react';
+import { useMyWorkspaces, useWorkspaceContext } from '@/api/hooks/workspaces';
+import { useWorkspaceStore, type WorkspaceInfo, type WorkspaceContextState } from '@/store/workspaceStore';
 import { useAuthStore } from '@/store/authStore';
 
-const STORAGE_KEY = 'leocrm-active-workspace';
-
 /**
  * Manages the active workspace for the current browser tab.
  *
- * Uses sessionStorage (per-tab, not shared across tabs) to store the active workspace ID.
- * Sends X-Workspace-ID header on workspace-aware requests.
+ * Uses the central workspaceStore (Zustand) for state management.
+ * sessionStorage provides per-tab persistence.
+ * X-Workspace-ID header is sent automatically by the API client interceptor.
  *
  * Workspaces are UI/navigation context only — they never affect permissions.
  */
 export function useWorkspace() {
-  const [activeWorkspaceId, setActiveWorkspaceId] = useState<string | null>(() => {
-    return sessionStorage.getItem(STORAGE_KEY);
-  });
+  const activeWorkspaceId = useWorkspaceStore(s => s.activeWorkspaceId);
+  const context = useWorkspaceStore(s => s.context);
+  const myWorkspacesFromStore = useWorkspaceStore(s => s.myWorkspaces);
+  const setActiveWorkspace = useWorkspaceStore(s => s.setActiveWorkspace);
+  const setContext = useWorkspaceStore(s => s.setContext);
+  const setMyWorkspaces = useWorkspaceStore(s => s.setMyWorkspaces);
+  const isModuleVisibleFromStore = useWorkspaceStore(s => s.isModuleVisible);
 
-  const { data: myWorkspaces } = useMyWorkspaces();
-  const { data: context } = useWorkspaceContext(activeWorkspaceId);
+  const user = useAuthStore.getState().user;
+  const isSystemAdmin = user?.is_system_admin;
+
+  // Fetch my workspaces and sync to store
+  const { data: myWorkspacesData } = useMyWorkspaces();
+  const { data: contextData } = useWorkspaceContext(activeWorkspaceId);
+
+  // Sync fetched workspaces to store
+  useEffect(() => {
+    if (myWorkspacesData?.items) {
+      setMyWorkspaces(myWorkspacesData.items as WorkspaceInfo[]);
+    }
+  }, [myWorkspacesData, setMyWorkspaces]);
+
+  // Sync fetched context to store
+  useEffect(() => {
+    if (contextData !== undefined) {
+      setContext(contextData as WorkspaceContextState | null);
+    }
+  }, [contextData, setContext]);
 
   // Auto-select default workspace if none selected
   useEffect(() => {
-    if (!activeWorkspaceId && myWorkspaces?.items?.length) {
-      const defaultWs = myWorkspaces.items.find(w => w.is_user_default) || myWorkspaces.items[0];
+    if (!activeWorkspaceId && myWorkspacesData?.items?.length) {
+      const defaultWs = myWorkspacesData.items.find(w => w.is_user_default) || myWorkspacesData.items[0];
       if (defaultWs) {
-        setActiveWorkspaceId(defaultWs.id);
-        sessionStorage.setItem(STORAGE_KEY, defaultWs.id);
+        setActiveWorkspace(defaultWs.id);
       }
     }
-  }, [activeWorkspaceId, myWorkspaces]);
+  }, [activeWorkspaceId, myWorkspacesData, setActiveWorkspace]);
 
   // Switch workspace (per-tab)
   const switchWorkspace = useCallback((workspaceId: string | null) => {
-    if (workspaceId) {
-      sessionStorage.setItem(STORAGE_KEY, workspaceId);
-    } else {
-      sessionStorage.removeItem(STORAGE_KEY);
-    }
-    setActiveWorkspaceId(workspaceId);
-  }, []);
-
-  // Get visible module keys from workspace context
-  const visibleModuleKeys: Set<string> = new Set(
-    context?.modules?.map(m => m.module_key) || []
-  );
+    setActiveWorkspace(workspaceId);
+  }, [setActiveWorkspace]);
 
   // Check if a module is visible in the current workspace
   const isModuleVisible = useCallback((moduleKey: string): boolean => {
-    // System admins see all modules regardless of workspace
-    const user = useAuthStore.getState().user;
-    if (user?.is_system_admin) return true;
-    // While permissions are loading (is_system_admin undefined), show everything
-    if (user && user.is_system_admin === undefined) return true;
-    // If no workspace context, show all (backward compatible)
-    if (!context?.workspace_id || !context?.modules?.length) return true;
-    return visibleModuleKeys.has(moduleKey);
-  }, [context, visibleModuleKeys]);
+    return isModuleVisibleFromStore(moduleKey, isSystemAdmin);
+  }, [isModuleVisibleFromStore, isSystemAdmin]);
+
+  const visibleModuleKeys = useWorkspaceStore(s => s.visibleModuleKeys());
 
   return {
     activeWorkspaceId,
     activeWorkspace: context,
-    myWorkspaces: myWorkspaces?.items || [],
+    myWorkspaces: myWorkspacesFromStore,
     switchWorkspace,
     isModuleVisible,
     visibleModuleKeys,
-    hasWorkspaces: (myWorkspaces?.items?.length || 0) > 0,
+    hasWorkspaces: myWorkspacesFromStore.length > 0,
   };
 }
diff --git a/frontend/src/pages/Settings.tsx b/frontend/src/pages/Settings.tsx
index 13fefc4..e82857a 100644
--- a/frontend/src/pages/Settings.tsx
+++ b/frontend/src/pages/Settings.tsx
@@ -23,6 +23,7 @@ export function SettingsPage() {
     { to: '/settings/notifications', label: t('settings.notifications'), icon: '\ud83d\udd14' },
     { to: '/settings/custom-fields', label: 'Custom Fields', icon: '\ud83d\udccb' },
     { to: '/settings/webhooks', label: 'Webhooks', icon: '\ud83d\udd14' },
+    { to: '/settings/workspaces', label: 'Workspaces', icon: '\ud83d\udd58\ufe0f' },
     { to: '/settings/backup', label: 'Backup & Restore', icon: '\ud83d\udcbe' },
   ];
 
diff --git a/frontend/src/pages/SettingsWorkspaces.tsx b/frontend/src/pages/SettingsWorkspaces.tsx
new file mode 100644
index 0000000..78a1b92
--- /dev/null
+++ b/frontend/src/pages/SettingsWorkspaces.tsx
@@ -0,0 +1,9 @@
+import { WorkspaceManager } from '@/components/settings/WorkspaceManager';
+
+export function WorkspaceManagerPage() {
+  return (
+    <div data-testid="settings-workspaces">
+      <WorkspaceManager />
+    </div>
+  );
+}
diff --git a/frontend/src/routes/index.tsx b/frontend/src/routes/index.tsx
index fbd5fd6..83f6bcc 100644
--- a/frontend/src/routes/index.tsx
+++ b/frontend/src/routes/index.tsx
@@ -64,6 +64,7 @@ const CustomFieldsPage = React.lazy(() => import('@/pages/CustomFields').then(m
 const ActivityTimelinePage = React.lazy(() => import('@/pages/ActivityTimeline').then(m => ({ default: m.ActivityTimelinePage })));
 const SettingsWebhooksPage = React.lazy(() => import('@/pages/SettingsWebhooks').then(m => ({ default: m.SettingsWebhooksPage })));
 const SettingsBackupPage = React.lazy(() => import('@/pages/SettingsBackup').then(m => ({ default: m.SettingsBackupPage })));
+const WorkspaceManagerPage = React.lazy(() => import('@/pages/SettingsWorkspaces').then(m => ({ default: m.WorkspaceManagerPage })));
 const SettingsRechtePage = React.lazy(() => import('@/pages/SettingsRechte').then(m => ({ default: m.SettingsRechtePage })));
 const NoAccessPage = React.lazy(() => import('@/pages/NoAccessPage').then(m => ({ default: m.NoAccessPage })));
 const StartPage = React.lazy(() => import('@/pages/StartPage').then(m => ({ default: m.StartPage })));
@@ -193,6 +194,7 @@ const router = createBrowserRouter([
           { path: 'menu', element: withSuspense(<SettingsMenuOrderPage />) },
           { path: 'custom-fields', element: withSuspense(<CustomFieldsPage />) },
           { path: 'webhooks', element: withSuspense(<SettingsWebhooksPage />) },
+          { path: 'workspaces', element: withSuspense(<WorkspaceManagerPage />) },
           { path: 'backup', element: withSuspense(<SettingsBackupPage />) },
           { path: 'rechte', element: <PermissionRoute permission="settings:read">{withSuspense(<SettingsRechtePage />)}</PermissionRoute> },
           { path: '*', element: <PluginRouteRenderer /> },
diff --git a/frontend/src/store/__tests__/workspaceStore.test.ts b/frontend/src/store/__tests__/workspaceStore.test.ts
new file mode 100644
index 0000000..02fc3d9
--- /dev/null
+++ b/frontend/src/store/__tests__/workspaceStore.test.ts
@@ -0,0 +1,135 @@
+import { describe, it, expect, beforeEach, vi } from 'vitest';
+import { useWorkspaceStore } from '@/store/workspaceStore';
+
+// Mock sessionStorage
+const mockSessionStorage = {
+  store: {} as Record<string, string>,
+  getItem: vi.fn((key: string) => mockSessionStorage.store[key] ?? null),
+  setItem: vi.fn((key: string, value: string) => { mockSessionStorage.store[key] = value; }),
+  removeItem: vi.fn((key: string) => { delete mockSessionStorage.store[key]; }),
+  clear: vi.fn(() => { mockSessionStorage.store = {}; }),
+};
+
+Object.defineProperty(window, 'sessionStorage', {
+  value: mockSessionStorage,
+  writable: true,
+});
+
+// Mock the API client import
+vi.mock('@/api/client', () => ({
+  setActiveWorkspaceId: vi.fn(),
+}));
+
+describe('workspaceStore', () => {
+  beforeEach(() => {
+    mockSessionStorage.clear();
+    useWorkspaceStore.getState().reset();
+  });
+
+  it('initializes with no active workspace', () => {
+    expect(useWorkspaceStore.getState().activeWorkspaceId).toBeNull();
+    expect(useWorkspaceStore.getState().context).toBeNull();
+    expect(useWorkspaceStore.getState().myWorkspaces).toEqual([]);
+  });
+
+  it('setActiveWorkspace stores ID in sessionStorage', () => {
+    const wsId = 'test-workspace-id';
+    useWorkspaceStore.getState().setActiveWorkspace(wsId);
+    expect(useWorkspaceStore.getState().activeWorkspaceId).toBe(wsId);
+    expect(mockSessionStorage.setItem).toHaveBeenCalledWith('leocrm-active-workspace', wsId);
+  });
+
+  it('setActiveWorkspace(null) removes from sessionStorage', () => {
+    useWorkspaceStore.getState().setActiveWorkspace('test-id');
+    useWorkspaceStore.getState().setActiveWorkspace(null);
+    expect(useWorkspaceStore.getState().activeWorkspaceId).toBeNull();
+    expect(mockSessionStorage.removeItem).toHaveBeenCalledWith('leocrm-active-workspace');
+  });
+
+  it('setActiveWorkspace clears context on switch', () => {
+    useWorkspaceStore.getState().setContext({
+      workspace_id: 'old-id',
+      modules: [{ module_key: 'contacts', menu_order: 0, config: {} }],
+      widgets: [],
+    });
+    useWorkspaceStore.getState().setActiveWorkspace('new-id');
+    expect(useWorkspaceStore.getState().context).toBeNull();
+  });
+
+  it('isModuleVisible returns true when no workspace context (backward compatible)', () => {
+    expect(useWorkspaceStore.getState().isModuleVisible('contacts')).toBe(true);
+  });
+
+  it('isModuleVisible returns true for system admin', () => {
+    useWorkspaceStore.getState().setContext({
+      workspace_id: 'ws-1',
+      modules: [{ module_key: 'contacts', menu_order: 0, config: {} }],
+      widgets: [],
+    });
+    expect(useWorkspaceStore.getState().isModuleVisible('mail', true)).toBe(true);
+  });
+
+  it('isModuleVisible returns false for module not in workspace', () => {
+    useWorkspaceStore.getState().setContext({
+      workspace_id: 'ws-1',
+      modules: [{ module_key: 'contacts', menu_order: 0, config: {} }],
+      widgets: [],
+    });
+    expect(useWorkspaceStore.getState().isModuleVisible('mail')).toBe(false);
+  });
+
+  it('isModuleVisible returns true for module in workspace', () => {
+    useWorkspaceStore.getState().setContext({
+      workspace_id: 'ws-1',
+      modules: [
+        { module_key: 'contacts', menu_order: 0, config: {} },
+        { module_key: 'calendar', menu_order: 1, config: {} },
+      ],
+      widgets: [],
+    });
+    expect(useWorkspaceStore.getState().isModuleVisible('contacts')).toBe(true);
+    expect(useWorkspaceStore.getState().isModuleVisible('calendar')).toBe(true);
+  });
+
+  it('visibleModuleKeys returns set of visible module keys', () => {
+    useWorkspaceStore.getState().setContext({
+      workspace_id: 'ws-1',
+      modules: [
+        { module_key: 'contacts', menu_order: 0, config: {} },
+        { module_key: 'calendar', menu_order: 1, config: {} },
+      ],
+      widgets: [],
+    });
+    const keys = useWorkspaceStore.getState().visibleModuleKeys();
+    expect(keys.has('contacts')).toBe(true);
+    expect(keys.has('calendar')).toBe(true);
+    expect(keys.has('mail')).toBe(false);
+  });
+
+  it('hasWorkspaces returns false when empty', () => {
+    expect(useWorkspaceStore.getState().hasWorkspaces()).toBe(false);
+  });
+
+  it('hasWorkspaces returns true when workspaces exist', () => {
+    useWorkspaceStore.getState().setMyWorkspaces([
+      { id: 'ws-1', name: 'WS1', icon: 'LayoutGrid', description: null, is_default: false, is_active: true },
+    ]);
+    expect(useWorkspaceStore.getState().hasWorkspaces()).toBe(true);
+  });
+
+  it('reset clears all state', () => {
+    useWorkspaceStore.getState().setActiveWorkspace('test-id');
+    useWorkspaceStore.getState().setMyWorkspaces([
+      { id: 'ws-1', name: 'WS1', icon: 'LayoutGrid', description: null, is_default: false, is_active: true },
+    ]);
+    useWorkspaceStore.getState().setContext({
+      workspace_id: 'ws-1',
+      modules: [],
+      widgets: [],
+    });
+    useWorkspaceStore.getState().reset();
+    expect(useWorkspaceStore.getState().activeWorkspaceId).toBeNull();
+    expect(useWorkspaceStore.getState().context).toBeNull();
+    expect(useWorkspaceStore.getState().myWorkspaces).toEqual([]);
+  });
+});
diff --git a/frontend/src/store/workspaceStore.ts b/frontend/src/store/workspaceStore.ts
new file mode 100644
index 0000000..f52a169
--- /dev/null
+++ b/frontend/src/store/workspaceStore.ts
@@ -0,0 +1,119 @@
+import { create } from 'zustand';
+import { persist, createJSONStorage } from 'zustand/middleware';
+import { setActiveWorkspaceId as setApiClientWorkspaceId } from '@/api/client';
+
+export interface WorkspaceModuleConfig {
+  module_key: string;
+  is_visible: boolean;
+  menu_order: number;
+  config: Record<string, any>;
+}
+
+export interface WorkspaceWidgetConfig {
+  id: string;
+  widget_key: string;
+  position_x: number;
+  position_y: number;
+  width: number;
+  height: number;
+  config: Record<string, any>;
+}
+
+export interface WorkspaceInfo {
+  id: string;
+  name: string;
+  icon: string;
+  description: string | null;
+  is_default: boolean;
+  is_active: boolean;
+  role?: 'member' | 'manager' | 'admin';
+  is_user_default?: boolean;
+  modules?: WorkspaceModuleConfig[];
+}
+
+export interface WorkspaceContextState {
+  workspace_id: string | null;
+  name?: string;
+  icon?: string;
+  role?: string;
+  modules: { module_key: string; menu_order: number; config: Record<string, any> }[];
+  widgets: WorkspaceWidgetConfig[];
+  error?: string;
+}
+
+interface WorkspaceStoreState {
+  // Active workspace ID (per-tab via sessionStorage)
+  activeWorkspaceId: string | null;
+  // Cached context
+  context: WorkspaceContextState | null;
+  // Available workspaces for the user
+  myWorkspaces: WorkspaceInfo[];
+  // Loading states
+  isLoading: boolean;
+  // Actions
+  setActiveWorkspace: (id: string | null) => void;
+  setContext: (ctx: WorkspaceContextState | null) => void;
+  setMyWorkspaces: (workspaces: WorkspaceInfo[]) => void;
+  setLoading: (loading: boolean) => void;
+  // Helpers
+  isModuleVisible: (moduleKey: string, isSystemAdmin?: boolean) => boolean;
+  visibleModuleKeys: () => Set<string>;
+  hasWorkspaces: () => boolean;
+  // Reset
+  reset: () => void;
+}
+
+const SESSION_STORAGE_KEY = 'leocrm-active-workspace';
+
+export const useWorkspaceStore = create<WorkspaceStoreState>()(
+  persist(
+    (set, get) => ({
+      activeWorkspaceId: sessionStorage.getItem(SESSION_STORAGE_KEY),
+      context: null,
+      myWorkspaces: [],
+      isLoading: false,
+
+      setActiveWorkspace: (id) => {
+        if (id) {
+          sessionStorage.setItem(SESSION_STORAGE_KEY, id);
+        } else {
+          sessionStorage.removeItem(SESSION_STORAGE_KEY);
+        }
+        setApiClientWorkspaceId(id);
+        set({ activeWorkspaceId: id, context: null });
+      },
+
+      setContext: (ctx) => set({ context: ctx }),
+
+      setMyWorkspaces: (workspaces) => set({ myWorkspaces: workspaces }),
+
+      setLoading: (loading) => set({ isLoading: loading }),
+
+      isModuleVisible: (moduleKey: string, isSystemAdmin?: boolean) => {
+        // System admins see all modules regardless of workspace
+        if (isSystemAdmin) return true;
+        // If no workspace context, show all (backward compatible)
+        const ctx = get().context;
+        if (!ctx?.workspace_id || !ctx?.modules?.length) return true;
+        return get().visibleModuleKeys().has(moduleKey);
+      },
+
+      visibleModuleKeys: () => {
+        const ctx = get().context;
+        return new Set(ctx?.modules?.map(m => m.module_key) || []);
+      },
+
+      hasWorkspaces: () => get().myWorkspaces.length > 0,
+
+      reset: () => {
+        sessionStorage.removeItem(SESSION_STORAGE_KEY);
+        set({ activeWorkspaceId: null, context: null, myWorkspaces: [], isLoading: false });
+      },
+    }),
+    {
+      name: 'leocrm-workspace-store',
+      storage: createJSONStorage(() => sessionStorage),
+      partialize: (state) => ({ activeWorkspaceId: state.activeWorkspaceId }),
+    }
+  )
+);
diff --git a/tests/test_workspaces.py b/tests/test_workspaces.py
new file mode 100644
index 0000000..67af132
--- /dev/null
+++ b/tests/test_workspaces.py
@@ -0,0 +1,632 @@
+"""Tests for Phase 6 — Workspaces.
+
+Covers:
+- Workspace CRUD (create, list, get, update, delete)
+- Module configuration (set modules, visibility)
+- Widget CRUD (create, list, update, delete, multiple same key)
+- User assignment (assign, remove, cross-tenant block)
+- Manager role check
+- Default workspace seeding
+- Set user default workspace
+- Workspace context (modules + widgets)
+- Empty workspace shows no modules
+- Cross-tenant isolation
+"""
+
+from __future__ import annotations
+
+import uuid
+
+import pytest
+from sqlalchemy import text
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.models.tenant import Tenant
+from app.models.user import User, UserTenant
+from app.models.workspace import Workspace, WorkspaceModule, WorkspaceUser, WorkspaceWidget
+from app.services import workspace_service
+
+
+# ─── Helpers ──────────────────────────────────────────────────
+
+
+async def _seed_tenant_and_user(db: AsyncSession) -> dict:
+    """Seed a tenant and a user, return IDs."""
+    tenant = Tenant(name="Test Tenant", slug="test-tenant")
+    db.add(tenant)
+    await db.flush()
+
+    user = User(
+        email="test@example.com",
+        name="Test User",
+        password_hash="dummy",
+        is_active=True,
+        preferences={},
+    )
+    db.add(user)
+    await db.flush()
+
+    ut = UserTenant(
+        user_id=user.id,
+        tenant_id=tenant.id,
+        is_default=True,
+        role="admin",
+    )
+    db.add(ut)
+    await db.flush()
+    return {"tenant": tenant, "user": user}
+
+
+async def _seed_second_tenant_and_user(db: AsyncSession) -> dict:
+    """Seed a second tenant and user for cross-tenant tests."""
+    tenant = Tenant(name="Other Tenant", slug="other-tenant")
+    db.add(tenant)
+    await db.flush()
+
+    user = User(
+        email="other@example.com",
+        name="Other User",
+        password_hash="dummy",
+        is_active=True,
+        preferences={},
+    )
+    db.add(user)
+    await db.flush()
+
+    ut = UserTenant(
+        user_id=user.id,
+        tenant_id=tenant.id,
+        is_default=True,
+        role="admin",
+    )
+    db.add(ut)
+    await db.flush()
+    return {"tenant": tenant, "user": user}
+
+
+# ─── Workspace CRUD ───────────────────────────────────────────
+
+
+@pytest.mark.asyncio
+async def test_create_workspace(db_session: AsyncSession):
+    """Creating a workspace returns correct data and auto-assigns creator as manager."""
+    seed = await _seed_tenant_and_user(db_session)
+    result = await workspace_service.create_workspace(
+        db_session, seed["tenant"].id, seed["user"].id,
+        name="Einkauf", icon="ShoppingCart", description="Einkauf-Workspace",
+    )
+    assert result["name"] == "Einkauf"
+    assert result["icon"] == "ShoppingCart"
+    assert result["is_active"] is True
+    assert result["user_count"] == 1  # Creator auto-assigned
+
+
+@pytest.mark.asyncio
+async def test_list_workspaces(db_session: AsyncSession):
+    """list_workspaces returns all active workspaces for a tenant."""
+    seed = await _seed_tenant_and_user(db_session)
+    await workspace_service.create_workspace(
+        db_session, seed["tenant"].id, seed["user"].id, name="WS1",
+    )
+    await workspace_service.create_workspace(
+        db_session, seed["tenant"].id, seed["user"].id, name="WS2",
+    )
+    result = await workspace_service.list_workspaces(db_session, seed["tenant"].id)
+    assert result["total"] == 2
+    names = [w["name"] for w in result["items"]]
+    assert "WS1" in names
+    assert "WS2" in names
+
+
+@pytest.mark.asyncio
+async def test_get_workspace(db_session: AsyncSession):
+    """get_workspace returns a single workspace with modules and user count."""
+    seed = await _seed_tenant_and_user(db_session)
+    created = await workspace_service.create_workspace(
+        db_session, seed["tenant"].id, seed["user"].id, name="TestWS",
+    )
+    ws_id = uuid.UUID(created["id"])
+    result = await workspace_service.get_workspace(db_session, seed["tenant"].id, ws_id)
+    assert result is not None
+    assert result["name"] == "TestWS"
+    assert result["user_count"] == 1
+
+
+@pytest.mark.asyncio
+async def test_update_workspace(db_session: AsyncSession):
+    """update_workspace changes name and description."""
+    seed = await _seed_tenant_and_user(db_session)
+    created = await workspace_service.create_workspace(
+        db_session, seed["tenant"].id, seed["user"].id, name="Original",
+    )
+    ws_id = uuid.UUID(created["id"])
+    result = await workspace_service.update_workspace(
+        db_session, seed["tenant"].id, ws_id,
+        name="Updated", description="New desc",
+    )
+    assert result is not None
+    assert result["name"] == "Updated"
+    assert result["description"] == "New desc"
+
+
+@pytest.mark.asyncio
+async def test_delete_workspace_soft_delete(db_session: AsyncSession):
+    """delete_workspace sets is_active=False (soft delete)."""
+    seed = await _seed_tenant_and_user(db_session)
+    created = await workspace_service.create_workspace(
+        db_session, seed["tenant"].id, seed["user"].id, name="ToDelete",
+    )
+    ws_id = uuid.UUID(created["id"])
+    deleted = await workspace_service.delete_workspace(db_session, seed["tenant"].id, ws_id)
+    assert deleted is True
+    # Should not appear in list (only active workspaces)
+    result = await workspace_service.list_workspaces(db_session, seed["tenant"].id)
+    assert result["total"] == 0
+
+
+@pytest.mark.asyncio
+async def test_default_workspace_uniqueness(db_session: AsyncSession):
+    """Setting a new default workspace unsets the previous default."""
+    seed = await _seed_tenant_and_user(db_session)
+    ws1 = await workspace_service.create_workspace(
+        db_session, seed["tenant"].id, seed["user"].id, name="WS1", is_default=True,
+    )
+    ws2 = await workspace_service.create_workspace(
+        db_session, seed["tenant"].id, seed["user"].id, name="WS2", is_default=True,
+    )
+    # ws1 should no longer be default
+    result1 = await workspace_service.get_workspace(db_session, seed["tenant"].id, uuid.UUID(ws1["id"]))
+    result2 = await workspace_service.get_workspace(db_session, seed["tenant"].id, uuid.UUID(ws2["id"]))
+    assert result1["is_default"] is False
+    assert result2["is_default"] is True
+
+
+# ─── Module Configuration ─────────────────────────────────────
+
+
+@pytest.mark.asyncio
+async def test_set_workspace_modules(db_session: AsyncSession):
+    """set_workspace_modules replaces all modules."""
+    seed = await _seed_tenant_and_user(db_session)
+    created = await workspace_service.create_workspace(
+        db_session, seed["tenant"].id, seed["user"].id, name="TestWS",
+    )
+    ws_id = uuid.UUID(created["id"])
+    modules = [
+        {"module_key": "contacts", "is_visible": True, "menu_order": 10, "config": {}},
+        {"module_key": "calendar", "is_visible": True, "menu_order": 20, "config": {}},
+        {"module_key": "mail", "is_visible": False, "menu_order": 30, "config": {}},
+    ]
+    result = await workspace_service.set_workspace_modules(db_session, seed["tenant"].id, ws_id, modules)
+    assert len(result) == 3
+    keys = [m["module_key"] for m in result]
+    assert "contacts" in keys
+    assert "calendar" in keys
+    assert "mail" in keys
+
+
+@pytest.mark.asyncio
+async def test_empty_workspace_shows_no_modules(db_session: AsyncSession):
+    """A workspace with no modules configured shows no modules in context."""
+    seed = await _seed_tenant_and_user(db_session)
+    created = await workspace_service.create_workspace(
+        db_session, seed["tenant"].id, seed["user"].id, name="EmptyWS",
+    )
+    ws_id = uuid.UUID(created["id"])
+    ctx = await workspace_service.get_workspace_context(
+        db_session, seed["tenant"].id, seed["user"].id, ws_id,
+    )
+    assert ctx is not None
+    assert ctx["modules"] == []
+
+
+@pytest.mark.asyncio
+async def test_hidden_module_not_in_context(db_session: AsyncSession):
+    """A module with is_visible=False does not appear in workspace context."""
+    seed = await _seed_tenant_and_user(db_session)
+    created = await workspace_service.create_workspace(
+        db_session, seed["tenant"].id, seed["user"].id, name="TestWS",
+    )
+    ws_id = uuid.UUID(created["id"])
+    modules = [
+        {"module_key": "contacts", "is_visible": True, "menu_order": 10, "config": {}},
+        {"module_key": "mail", "is_visible": False, "menu_order": 20, "config": {}},
+    ]
+    await workspace_service.set_workspace_modules(db_session, seed["tenant"].id, ws_id, modules)
+    ctx = await workspace_service.get_workspace_context(
+        db_session, seed["tenant"].id, seed["user"].id, ws_id,
+    )
+    assert ctx is not None
+    module_keys = [m["module_key"] for m in ctx["modules"]]
+    assert "contacts" in module_keys
+    assert "mail" not in module_keys  # Hidden module not in context
+
+
+# ─── Widget CRUD ──────────────────────────────────────────────
+
+
+@pytest.mark.asyncio
+async def test_create_widget(db_session: AsyncSession):
+    """Creating a widget returns correct data."""
+    seed = await _seed_tenant_and_user(db_session)
+    created = await workspace_service.create_workspace(
+        db_session, seed["tenant"].id, seed["user"].id, name="TestWS",
+    )
+    ws_id = uuid.UUID(created["id"])
+    result = await workspace_service.create_widget(
+        db_session, seed["tenant"].id, ws_id,
+        widget_key="recent_contacts", position_x=0, position_y=0, width=2, height=1,
+    )
+    assert result["widget_key"] == "recent_contacts"
+    assert result["width"] == 2
+    assert result["height"] == 1
+
+
+@pytest.mark.asyncio
+async def test_list_widgets(db_session: AsyncSession):
+    """list_widgets returns all widgets for a workspace."""
+    seed = await _seed_tenant_and_user(db_session)
+    created = await workspace_service.create_workspace(
+        db_session, seed["tenant"].id, seed["user"].id, name="TestWS",
+    )
+    ws_id = uuid.UUID(created["id"])
+    await workspace_service.create_widget(
+        db_session, seed["tenant"].id, ws_id, widget_key="widget_a", position_y=0,
+    )
+    await workspace_service.create_widget(
+        db_session, seed["tenant"].id, ws_id, widget_key="widget_b", position_y=1,
+    )
+    result = await workspace_service.get_widgets(db_session, seed["tenant"].id, ws_id)
+    assert len(result) == 2
+
+
+@pytest.mark.asyncio
+async def test_multiple_same_widget_key(db_session: AsyncSession):
+    """Multiple instances of the same widget_key can exist (no unique constraint)."""
+    seed = await _seed_tenant_and_user(db_session)
+    created = await workspace_service.create_workspace(
+        db_session, seed["tenant"].id, seed["user"].id, name="TestWS",
+    )
+    ws_id = uuid.UUID(created["id"])
+    w1 = await workspace_service.create_widget(
+        db_session, seed["tenant"].id, ws_id, widget_key="calendar_upcoming", position_x=0, position_y=0,
+    )
+    w2 = await workspace_service.create_widget(
+        db_session, seed["tenant"].id, ws_id, widget_key="calendar_upcoming", position_x=1, position_y=0,
+    )
+    assert w1["id"] != w2["id"]  # Different IDs
+    assert w1["widget_key"] == w2["widget_key"]  # Same key
+    result = await workspace_service.get_widgets(db_session, seed["tenant"].id, ws_id)
+    assert len(result) == 2  # Both exist
+
+
+@pytest.mark.asyncio
+async def test_update_widget(db_session: AsyncSession):
+    """update_widget changes position and size."""
+    seed = await _seed_tenant_and_user(db_session)
+    created = await workspace_service.create_workspace(
+        db_session, seed["tenant"].id, seed["user"].id, name="TestWS",
+    )
+    ws_id = uuid.UUID(created["id"])
+    widget = await workspace_service.create_widget(
+        db_session, seed["tenant"].id, ws_id, widget_key="test_widget",
+    )
+    widget_id = uuid.UUID(widget["id"])
+    result = await workspace_service.update_widget(
+        db_session, seed["tenant"].id, widget_id,
+        position_x=2, position_y=3, width=4, height=2,
+    )
+    assert result is not None
+    assert result["position_x"] == 2
+    assert result["position_y"] == 3
+    assert result["width"] == 4
+    assert result["height"] == 2
+
+
+@pytest.mark.asyncio
+async def test_delete_widget(db_session: AsyncSession):
+    """delete_widget removes the widget."""
+    seed = await _seed_tenant_and_user(db_session)
+    created = await workspace_service.create_workspace(
+        db_session, seed["tenant"].id, seed["user"].id, name="TestWS",
+    )
+    ws_id = uuid.UUID(created["id"])
+    widget = await workspace_service.create_widget(
+        db_session, seed["tenant"].id, ws_id, widget_key="test_widget",
+    )
+    widget_id = uuid.UUID(widget["id"])
+    deleted = await workspace_service.delete_widget(db_session, seed["tenant"].id, widget_id)
+    assert deleted is True
+    result = await workspace_service.get_widgets(db_session, seed["tenant"].id, ws_id)
+    assert len(result) == 0
+
+
+# ─── User Assignment ──────────────────────────────────────────
+
+
+@pytest.mark.asyncio
+async def test_assign_user_to_workspace(db_session: AsyncSession):
+    """assign_user adds a user to a workspace."""
+    seed = await _seed_tenant_and_user(db_session)
+    created = await workspace_service.create_workspace(
+        db_session, seed["tenant"].id, seed["user"].id, name="TestWS",
+    )
+    ws_id = uuid.UUID(created["id"])
+    # Create a second user in the same tenant
+    user2 = User(
+        email="user2@example.com", name="User 2", password_hash="dummy",
+        is_active=True, preferences={},
+    )
+    db_session.add(user2)
+    await db_session.flush()
+    ut2 = UserTenant(user_id=user2.id, tenant_id=seed["tenant"].id, is_default=True, role="viewer")
+    db_session.add(ut2)
+    await db_session.flush()
+
+    result = await workspace_service.assign_user(
+        db_session, seed["tenant"].id, ws_id, user2.id, role="member",
+    )
+    assert result["role"] == "member"
+    assert result["user_id"] == str(user2.id)
+
+
+@pytest.mark.asyncio
+async def test_remove_user_from_workspace(db_session: AsyncSession):
+    """remove_user removes a user from a workspace."""
+    seed = await _seed_tenant_and_user(db_session)
+    created = await workspace_service.create_workspace(
+        db_session, seed["tenant"].id, seed["user"].id, name="TestWS",
+    )
+    ws_id = uuid.UUID(created["id"])
+    # Create a second user
+    user2 = User(
+        email="user2@example.com", name="User 2", password_hash="dummy",
+        is_active=True, preferences={},
+    )
+    db_session.add(user2)
+    await db_session.flush()
+    ut2 = UserTenant(user_id=user2.id, tenant_id=seed["tenant"].id, is_default=True, role="viewer")
+    db_session.add(ut2)
+    await db_session.flush()
+
+    await workspace_service.assign_user(
+        db_session, seed["tenant"].id, ws_id, user2.id, role="member",
+    )
+    removed = await workspace_service.remove_user(
+        db_session, seed["tenant"].id, ws_id, user2.id,
+    )
+    assert removed is True
+
+
+@pytest.mark.asyncio
+async def test_cross_tenant_user_assignment_blocked(db_session: AsyncSession):
+    """verify_user_same_tenant returns False for a user from a different tenant."""
+    seed_a = await _seed_tenant_and_user(db_session)
+    seed_b = await _seed_second_tenant_and_user(db_session)
+
+    # User B should not be assignable to tenant A's workspace
+    result = await workspace_service.verify_user_same_tenant(
+        db_session, seed_a["tenant"].id, seed_b["user"].id,
+    )
+    assert result is False
+
+    # User A should be verified for tenant A
+    result = await workspace_service.verify_user_same_tenant(
+        db_session, seed_a["tenant"].id, seed_a["user"].id,
+    )
+    assert result is True
+
+
+# ─── Manager Role Check ───────────────────────────────────────
+
+
+@pytest.mark.asyncio
+async def test_is_workspace_manager(db_session: AsyncSession):
+    """Creator is auto-assigned as manager; a regular member is not a manager."""
+    seed = await _seed_tenant_and_user(db_session)
+    created = await workspace_service.create_workspace(
+        db_session, seed["tenant"].id, seed["user"].id, name="TestWS",
+    )
+    ws_id = uuid.UUID(created["id"])
+
+    # Creator should be manager
+    is_mgr = await workspace_service.is_workspace_manager(
+        db_session, seed["tenant"].id, ws_id, seed["user"].id,
+    )
+    assert is_mgr is True
+
+    # Create a member (not manager)
+    user2 = User(
+        email="member@example.com", name="Member", password_hash="dummy",
+        is_active=True, preferences={},
+    )
+    db_session.add(user2)
+    await db_session.flush()
+    ut2 = UserTenant(user_id=user2.id, tenant_id=seed["tenant"].id, is_default=True, role="viewer")
+    db_session.add(ut2)
+    await db_session.flush()
+
+    await workspace_service.assign_user(
+        db_session, seed["tenant"].id, ws_id, user2.id, role="member",
+    )
+
+    is_mgr2 = await workspace_service.is_workspace_manager(
+        db_session, seed["tenant"].id, ws_id, user2.id,
+    )
+    assert is_mgr2 is False
+
+
+# ─── Default Workspace Seeding ────────────────────────────────
+
+
+@pytest.mark.asyncio
+async def test_seed_default_workspace(db_session: AsyncSession):
+    """seed_default_workspace creates a default workspace with all standard modules."""
+    seed = await _seed_tenant_and_user(db_session)
+    result = await workspace_service.seed_default_workspace(
+        db_session, seed["tenant"].id, seed["user"].id,
+    )
+    assert result is not None
+    assert result["name"] == "Standard"
+    assert result["is_default"] is True
+    assert result["user_count"] == 1
+
+
+@pytest.mark.asyncio
+async def test_seed_default_workspace_idempotent(db_session: AsyncSession):
+    """seed_default_workspace returns None if workspaces already exist."""
+    seed = await _seed_tenant_and_user(db_session)
+    # First call creates the default workspace
+    await workspace_service.seed_default_workspace(
+        db_session, seed["tenant"].id, seed["user"].id,
+    )
+    # Second call should return None (already has workspaces)
+    result = await workspace_service.seed_default_workspace(
+        db_session, seed["tenant"].id, seed["user"].id,
+    )
+    assert result is None
+
+
+# ─── Set User Default Workspace ───────────────────────────────
+
+
+@pytest.mark.asyncio
+async def test_set_user_default_workspace(db_session: AsyncSession):
+    """set_user_default_workspace sets a workspace as default and unsets others."""
+    seed = await _seed_tenant_and_user(db_session)
+    ws1 = await workspace_service.create_workspace(
+        db_session, seed["tenant"].id, seed["user"].id, name="WS1",
+    )
+    ws2 = await workspace_service.create_workspace(
+        db_session, seed["tenant"].id, seed["user"].id, name="WS2",
+    )
+    ws1_id = uuid.UUID(ws1["id"])
+    ws2_id = uuid.UUID(ws2["id"])
+
+    # Assign user to both
+    # (creator is already auto-assigned to both as manager)
+
+    # Set WS2 as default
+    await workspace_service.set_user_default_workspace(
+        db_session, seed["tenant"].id, seed["user"].id, ws2_id,
+    )
+
+    # Verify via get_my_workspaces
+    my = await workspace_service.get_my_workspaces(
+        db_session, seed["tenant"].id, seed["user"].id,
+    )
+    for item in my["items"]:
+        if item["id"] == ws2["id"]:
+            assert item["is_user_default"] is True
+        elif item["id"] == ws1["id"]:
+            assert item["is_user_default"] is False
+
+
+# ─── Workspace Context ────────────────────────────────────────
+
+
+@pytest.mark.asyncio
+async def test_workspace_context_includes_modules_and_widgets(db_session: AsyncSession):
+    """get_workspace_context returns both modules and widgets."""
+    seed = await _seed_tenant_and_user(db_session)
+    created = await workspace_service.create_workspace(
+        db_session, seed["tenant"].id, seed["user"].id, name="TestWS",
+    )
+    ws_id = uuid.UUID(created["id"])
+
+    # Set modules
+    await workspace_service.set_workspace_modules(
+        db_session, seed["tenant"].id, ws_id,
+        [{"module_key": "contacts", "is_visible": True, "menu_order": 10, "config": {}}],
+    )
+
+    # Create widget
+    await workspace_service.create_widget(
+        db_session, seed["tenant"].id, ws_id, widget_key="recent_contacts",
+    )
+
+    ctx = await workspace_service.get_workspace_context(
+        db_session, seed["tenant"].id, seed["user"].id, ws_id,
+    )
+    assert ctx is not None
+    assert len(ctx["modules"]) == 1
+    assert ctx["modules"][0]["module_key"] == "contacts"
+    assert len(ctx["widgets"]) == 1
+    assert ctx["widgets"][0]["widget_key"] == "recent_contacts"
+
+
+@pytest.mark.asyncio
+async def test_workspace_context_unassigned_user(db_session: AsyncSession):
+    """get_workspace_context returns None for an unassigned user."""
+    seed = await _seed_tenant_and_user(db_session)
+    created = await workspace_service.create_workspace(
+        db_session, seed["tenant"].id, seed["user"].id, name="TestWS",
+    )
+    ws_id = uuid.UUID(created["id"])
+
+    # Create a second user NOT assigned to the workspace
+    user2 = User(
+        email="unassigned@example.com", name="Unassigned", password_hash="dummy",
+        is_active=True, preferences={},
+    )
+    db_session.add(user2)
+    await db_session.flush()
+    ut2 = UserTenant(user_id=user2.id, tenant_id=seed["tenant"].id, is_default=True, role="viewer")
+    db_session.add(ut2)
+    await db_session.flush()
+
+    ctx = await workspace_service.get_workspace_context(
+        db_session, seed["tenant"].id, user2.id, ws_id,
+    )
+    assert ctx is None  # User not assigned
+
+
+# ─── Cross-Tenant Isolation ───────────────────────────────────
+
+
+@pytest.mark.asyncio
+async def test_cross_tenant_workspace_isolation(db_session: AsyncSession):
+    """A workspace from tenant A cannot be accessed by tenant B."""
+    seed_a = await _seed_tenant_and_user(db_session)
+    seed_b = await _seed_second_tenant_and_user(db_session)
+
+    created = await workspace_service.create_workspace(
+        db_session, seed_a["tenant"].id, seed_a["user"].id, name="TenantA_WS",
+    )
+    ws_id = uuid.UUID(created["id"])
+
+    # Tenant B should not see tenant A's workspace
+    result = await workspace_service.get_workspace(
+        db_session, seed_b["tenant"].id, ws_id,
+    )
+    assert result is None  # Not found in tenant B
+
+
+@pytest.mark.asyncio
+async def test_get_my_workspaces_only_assigned(db_session: AsyncSession):
+    """get_my_workspaces returns only workspaces the user is assigned to."""
+    seed = await _seed_tenant_and_user(db_session)
+    ws1 = await workspace_service.create_workspace(
+        db_session, seed["tenant"].id, seed["user"].id, name="AssignedWS",
+    )
+    ws2 = await workspace_service.create_workspace(
+        db_session, seed["tenant"].id, seed["user"].id, name="AlsoAssignedWS",
+    )
+
+    # Create a third workspace without assigning the user
+    ws3 = Workspace(
+        tenant_id=seed["tenant"].id,
+        name="UnassignedWS",
+        is_active=True,
+        created_by=seed["user"].id,
+    )
+    db_session.add(ws3)
+    await db_session.flush()
+
+    my = await workspace_service.get_my_workspaces(
+        db_session, seed["tenant"].id, seed["user"].id,
+    )
+    names = [w["name"] for w in my["items"]]
+    assert "AssignedWS" in names
+    assert "AlsoAssignedWS" in names
+    assert "UnassignedWS" not in names  # User not assigned