fix(hdx-eval): reject invalid MCP evidence content (#3532)

Fixes #3526.

`queryTileWithEvidence` now reports a failed query when an MCP transport
succeeds but the returned content is not valid JSON. Malformed text no longer
counts as evidence with `success: true`. Empty or whitespace-only content keeps
the existing successful no-data behavior.

Added regression coverage for malformed content, empty content, valid rows, and
valid content without a result.

Validation:

- `yarn workspace @hyperdx/hdx-eval lint`
- `yarn workspace @hyperdx/hdx-eval tsc --noEmit`
- `yarn workspace @hyperdx/hdx-eval jest --runInBand src/__tests__/api.test.ts --coverage=false` (4 passed)
- Full hdx-eval tests: 413 passed; 2 unrelated Windows path assertions failed in
  `src/__tests__/runPath.test.ts` because the fixture expects `\tmp\...` while
  Windows returns `C:\tmp\...`.

Author: jiangyuer018

packages/hdx-eval/src/__tests__/api.test.ts

@@ -0,0 +1,105 @@
+import { HyperdxApiClient } from '@/hyperdx/api';
+
+const originalFetch = global.fetch;
+
+function mockMcpContent(text: string): void {
+  global.fetch = jest.fn().mockResolvedValue({
+    ok: true,
+    status: 200,
+    text: async () =>
+      JSON.stringify({
+        jsonrpc: '2.0',
+        result: {
+          content: [{ type: 'text', text }],
+        },
+      }),
+  }) as unknown as typeof fetch;
+}
+
+afterEach(() => {
+  global.fetch = originalFetch;
+});
+
+describe('HyperdxApiClient', () => {
+  it('reports invalid MCP content as a failed tile query', async () => {
+    mockMcpContent('not valid JSON');
+
+    const result = await new HyperdxApiClient(
+      'http://localhost',
+    ).queryTileWithEvidence({
+      accessKey: 'test-key',
+      dashboardId: 'dashboard-id',
+      tileId: 'tile-id',
+      startTime: '2026-01-01T00:00:00.000Z',
+      endTime: '2026-01-01T01:00:00.000Z',
+    });
+
+    expect(result.success).toBe(false);
+    expect(result.hasData).toBe(false);
+    expect(result.error).toMatch(/^Invalid MCP content:/);
+  });
+
+  it('treats empty MCP content as a successful query with no data', async () => {
+    mockMcpContent(' \n');
+
+    const result = await new HyperdxApiClient(
+      'http://localhost',
+    ).queryTileWithEvidence({
+      accessKey: 'test-key',
+      dashboardId: 'dashboard-id',
+      tileId: 'tile-id',
+      startTime: '2026-01-01T00:00:00.000Z',
+      endTime: '2026-01-01T01:00:00.000Z',
+    });
+
+    expect(result).toEqual({ success: true, hasData: false });
+  });
+
+  it('extracts rows and groups from valid MCP content', async () => {
+    mockMcpContent(
+      JSON.stringify({
+        result: [
+          { ServiceName: 'api', value: 1 },
+          { ServiceName: 'worker', value: 2 },
+        ],
+      }),
+    );
+
+    const result = await new HyperdxApiClient(
+      'http://localhost',
+    ).queryTileWithEvidence({
+      accessKey: 'test-key',
+      dashboardId: 'dashboard-id',
+      tileId: 'tile-id',
+      startTime: '2026-01-01T00:00:00.000Z',
+      endTime: '2026-01-01T01:00:00.000Z',
+    });
+
+    expect(result).toEqual({
+      success: true,
+      hasData: true,
+      rowCount: 2,
+      groupCount: 2,
+      sampleRows: [
+        { ServiceName: 'api', value: 1 },
+        { ServiceName: 'worker', value: 2 },
+      ],
+    });
+  });
+
+  it('treats valid MCP content without a result as no data', async () => {
+    mockMcpContent('{}');
+
+    const result = await new HyperdxApiClient(
+      'http://localhost',
+    ).queryTileWithEvidence({
+      accessKey: 'test-key',
+      dashboardId: 'dashboard-id',
+      tileId: 'tile-id',
+      startTime: '2026-01-01T00:00:00.000Z',
+      endTime: '2026-01-01T01:00:00.000Z',
+    });
+
+    expect(result).toEqual({ success: true, hasData: false });
+  });
+});

packages/hdx-eval/src/hyperdx/api.ts

@@ -325,6 +325,10 @@ export class HyperdxApiClient {
       };
     }
 
+    if (!content.text.trim()) {
+      return { success: true, hasData: false };
+    }
+
     try {
       const inner = JSON.parse(content.text);
       const result = inner.result;
@@ -368,8 +372,14 @@ export class HyperdxApiClient {
         groupCount,
         sampleRows: rows.slice(0, 5),
       };
-    } catch {
-      return { success: true, hasData: content.text.length > 0 };
+    } catch (error) {
+      return {
+        success: false,
+        hasData: false,
+        error: `Invalid MCP content: ${
+          error instanceof Error ? error.message : String(error)
+        }`.slice(0, 300),
+      };
     }
   }
 }