fix: address all 3 PR review comments

1. Default metric aggregation groupBy to '_all' instead of 'name' for
   single-bucket results in DashboardRenderer.
2. Reset fetchedValue/error in ObjectMetricWidget when dataSource becomes
   unavailable, preventing stale server data from masking fallback values.
3. Add test with failing dataSource to verify error state routing in
   DashboardRenderer object-metric path.

Agent-Logs-Url: https://github.com/objectstack-ai/objectui/sessions/7a05b366-541b-4772-8f1f-91bcb9a25ff7

Co-authored-by: xuyushun441-sys <255036401+xuyushun441-sys@users.noreply.github.com>

Author: Copilot

packages/plugin-dashboard/src/DashboardRenderer.tsx

@@ -135,12 +135,14 @@ export const DashboardRenderer = forwardRef<HTMLDivElement, DashboardRendererPro
                     ? {
                         field: widget.valueField || widgetData.aggregate.field,
                         function: widget.aggregate || widgetData.aggregate.function,
-                        groupBy: widget.categoryField || widgetData.aggregate.groupBy,
+                        // Prefer explicit categoryField or aggregate.groupBy; otherwise, default to a single bucket.
+                        groupBy: widget.categoryField ?? widgetData.aggregate.groupBy ?? '_all',
                     }
                     : widget.aggregate ? {
                         field: widget.valueField || 'value',
                         function: widget.aggregate,
-                        groupBy: widget.categoryField || 'name',
+                        // Default to a single group unless the user explicitly configures a categoryField.
+                        groupBy: widget.categoryField || '_all',
                     } : undefined;
 
                 return {

packages/plugin-dashboard/src/ObjectMetricWidget.tsx

@@ -127,6 +127,11 @@ export const ObjectMetricWidget: React.FC<ObjectMetricWidgetProps> = ({
 
     if (dataSource && objectName) {
       fetchMetric(dataSource, mounted);
+    } else {
+      // Reset state when dataSource becomes unavailable so we fall back
+      // to the static fallbackValue instead of showing stale server data.
+      setFetchedValue(null);
+      setError(null);
     }
 
     return () => { mounted.current = false; };

packages/plugin-dashboard/src/__tests__/DashboardRenderer.widgetData.test.tsx

@@ -6,8 +6,9 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import { describe, it, expect } from 'vitest';
-import { render } from '@testing-library/react';
+import { describe, it, expect, vi } from 'vitest';
+import { render, waitFor } from '@testing-library/react';
+import { SchemaRendererProvider } from '@object-ui/react';
 import { DashboardRenderer } from '../DashboardRenderer';
 
 /**
@@ -1365,4 +1366,46 @@ describe('DashboardRenderer widget data extraction', () => {
     expect(container.textContent).toContain('Revenue Sum');
     expect(container.textContent).toContain('$0');
   });
+
+  it('should show error state when object-metric dataSource fails', async () => {
+    const dataSource = {
+      aggregate: vi.fn().mockRejectedValue(new Error('Cube name is required')),
+      find: vi.fn(),
+    };
+
+    const schema = {
+      type: 'dashboard' as const,
+      name: 'test',
+      title: 'Test',
+      widgets: [
+        {
+          type: 'metric',
+          object: 'opportunity',
+          aggregate: 'sum',
+          valueField: 'amount',
+          layout: { x: 0, y: 0, w: 1, h: 1 },
+          options: {
+            label: 'Revenue',
+            value: '$999',
+          },
+        },
+      ],
+    } as any;
+
+    const { container } = render(
+      <SchemaRendererProvider dataSource={dataSource}>
+        <DashboardRenderer schema={schema} />
+      </SchemaRendererProvider>,
+    );
+
+    // Should display the error from the failing aggregate, not the fallback value
+    await waitFor(() => {
+      const errorEl = container.querySelector('[data-testid="metric-error"]');
+      expect(errorEl).toBeTruthy();
+    });
+
+    expect(container.textContent).toContain('Revenue');
+    expect(container.textContent).toContain('Cube name is required');
+    expect(container.textContent).not.toContain('$999');
+  });
 });