test: add regression test for non-string serverLogs (#8460) (#11268)

## Summary

Add a regression test for #8460 (handle non-string `serverLogs` in error
report). The fix added `typeof error.serverLogs === 'string' ? ... :
JSON.stringify(...)` in `errorReportUtil.ts` so object-shaped logs no
longer render as `[object Object]`. There was no existing unit test for
`generateErrorReport`, so this regression could silently return.

## Changes

- **What**: New unit test file `src/utils/errorReportUtil.test.ts`
covering `generateErrorReport`'s `serverLogs` rendering.
- String case: verifies plain-string logs still appear verbatim and
`[object Object]` is absent.
- Object case (regression for #8460): verifies object logs are
JSON-stringified instead of coerced to `[object Object]`.
- Verified RED→GREEN locally.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-11268-test-add-regression-test-for-non-string-serverLogs-8460-3436d73d36508195a32fc559ab7ce5bb)
by [Unito](https://www.unito.io)

src/utils/errorReportUtil.test.ts

@@ -0,0 +1,52 @@
+import { describe, expect, it } from 'vitest'
+
+import type { ISerialisedGraph } from '@/lib/litegraph/src/litegraph'
+import type { SystemStats } from '@/schemas/apiSchema'
+
+import type { ErrorReportData } from './errorReportUtil'
+import { generateErrorReport } from './errorReportUtil'
+
+const baseSystemStats: SystemStats = {
+  system: {
+    os: 'linux',
+    comfyui_version: '1.0.0',
+    python_version: '3.11',
+    pytorch_version: '2.0',
+    embedded_python: false,
+    argv: ['main.py'],
+    ram_total: 0,
+    ram_free: 0
+  },
+  devices: []
+}
+
+const baseWorkflow = { nodes: [], links: [] } as unknown as ISerialisedGraph
+
+function buildError(serverLogs: unknown): ErrorReportData {
+  return {
+    exceptionType: 'RuntimeError',
+    exceptionMessage: 'boom',
+    systemStats: baseSystemStats,
+    serverLogs: serverLogs as string,
+    workflow: baseWorkflow
+  }
+}
+
+describe('generateErrorReport', () => {
+  it('embeds string serverLogs verbatim', () => {
+    const report = generateErrorReport(buildError('line one\nline two'))
+
+    expect(report).toContain('line one\nline two')
+    expect(report).not.toContain('[object Object]')
+  })
+
+  it('stringifies object serverLogs instead of rendering [object Object]', () => {
+    const report = generateErrorReport(
+      buildError({ entries: [{ msg: 'hello' }] })
+    )
+
+    expect(report).not.toContain('[object Object]')
+    expect(report).toContain('"entries"')
+    expect(report).toContain('"msg": "hello"')
+  })
+})