diff --git a/server/services/insightsService.test.js b/server/services/insightsService.test.js
index 1d68f32f6b..295a0e9f8c 100644
--- a/server/services/insightsService.test.js
+++ b/server/services/insightsService.test.js
@@ -1,21 +1,43 @@
-import { describe, it, expect, vi, beforeEach } from 'vitest';
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
 
 // Mock the provider-readiness check so any code path that touches it runs offline.
 vi.mock('./ollamaManager.js', () => ({
   ensureProviderReady: vi.fn().mockResolvedValue({ success: true }),
 }));
-// generateThemeAnalysis/refreshCrossDomainNarrative now call the shared
+// generateThemeAnalysis/refreshCrossDomainNarrative call the shared
 // aiProvider.callProviderAISimple transport (see aiProvider.test.js for its own
-// contract coverage) — stub only that export so the disk-only read paths below
-// can assert it's never reached, while stripCodeFences/parseLLMJSON (also
-// imported from this module) stay real.
+// contract coverage) — stub only that export, while stripCodeFences/parseLLMJSON
+// (also imported from this module) stay real.
 vi.mock('./aiProvider.js', async (importOriginal) => {
   const actual = await importOriginal();
   return { ...actual, callProviderAISimple: vi.fn() };
 });
+// `atomicWrite` is the assertion surface for the persist guard below. Keep the
+// rest of fileUtils real — `PATHS` is read at insightsService module scope, so a
+// mock that omits it breaks the import outright.
+vi.mock('../lib/fileUtils.js', async (importOriginal) => {
+  const actual = await importOriginal();
+  return { ...actual, atomicWrite: vi.fn(), ensureDir: vi.fn(), readJSONFile: vi.fn() };
+});
+vi.mock('./providers.js', () => ({
+  getActiveProvider: vi.fn(),
+  getProviderById: vi.fn(),
+}));
+vi.mock('./taste-questionnaire.js', () => ({ getTasteProfile: vi.fn() }));
+vi.mock('./genome.js', () => ({ getGenomeSummary: vi.fn().mockResolvedValue(null) }));
+vi.mock('./meatspaceHealth.js', () => ({ getBloodTests: vi.fn().mockResolvedValue([]) }));
+vi.mock('./appleHealthQuery.js', () => ({ getCorrelationData: vi.fn().mockResolvedValue(null) }));
 
 import { callProviderAISimple } from './aiProvider.js';
-import { getThemeAnalysis, getCrossDomainNarrative } from './insightsService.js';
+import { atomicWrite, readJSONFile } from '../lib/fileUtils.js';
+import { getActiveProvider } from './providers.js';
+import { getTasteProfile } from './taste-questionnaire.js';
+import {
+  getThemeAnalysis,
+  getCrossDomainNarrative,
+  generateThemeAnalysis,
+  refreshCrossDomainNarrative,
+} from './insightsService.js';
 
 // Enforces the no-cold-bootstrap trigger contract documented at the generation
 // entry points: the cached-read paths the Insights page mounts with must be
@@ -23,19 +45,90 @@ import { getThemeAnalysis, getCrossDomainNarrative } from './insightsService.js'
 // endpoints may generate. If a future edit makes a read path warm the cache via
 // the LLM, this fails.
 describe('insightsService read paths — disk-only, no provider call', () => {
+  let fetchSpy;
+
   beforeEach(() => {
     vi.clearAllMocks();
+    readJSONFile.mockResolvedValue(null);
+    // The export-level spy below only catches a read path that reaches a provider
+    // through `callProviderAISimple`. The contract is broader than one export —
+    // "no outbound provider call by ANY transport" — so pin it at the wire too,
+    // where a direct fetch, a streaming helper, or a future second transport
+    // would still have to pass.
+    fetchSpy = vi.fn();
+    vi.stubGlobal('fetch', fetchSpy);
+  });
+
+  afterEach(() => {
+    vi.unstubAllGlobals();
   });
 
   it('getThemeAnalysis performs no provider call (returns not_generated when uncached)', async () => {
     const result = await getThemeAnalysis();
     expect(callProviderAISimple).not.toHaveBeenCalled();
+    expect(fetchSpy).not.toHaveBeenCalled();
     expect(result.available === false || result.available === true).toBe(true);
   });
 
   it('getCrossDomainNarrative performs no provider call (returns not_generated when uncached)', async () => {
     const result = await getCrossDomainNarrative();
     expect(callProviderAISimple).not.toHaveBeenCalled();
+    expect(fetchSpy).not.toHaveBeenCalled();
     expect(result.available === false || result.available === true).toBe(true);
   });
 });
+
+// The bug #5617 describes, pinned at the Insights boundary rather than only at
+// the transport: both generators persist unconditionally once `result.error` is
+// unset, so a transport that misclassifies a failed call as a successful empty
+// completion overwrites a real cached theme/narrative with nothing. The shared
+// aiProvider transport classifies that as an error — these assert the callers
+// actually honour it and leave the cache alone.
+describe('insightsService generation — a provider error never overwrites the cache', () => {
+  const CACHED_THEMES = {
+    themes: [{ title: 'Cached theme', strength: 'strong', narrative: 'prior', evidence: [] }],
+    generatedAt: '2020-01-01T00:00:00.000Z',
+    model: 'model-1',
+  };
+
+  beforeEach(() => {
+    vi.clearAllMocks();
+    getActiveProvider.mockResolvedValue({
+      id: 'provider-1', name: 'Example Provider', type: 'api',
+      endpoint: 'https://api.example.com/v1', defaultModel: 'model-1',
+    });
+    getTasteProfile.mockResolvedValue({
+      sections: [{ label: 'Music', summary: 'Prefers sparse arrangements.' }],
+    });
+    readJSONFile.mockResolvedValue(CACHED_THEMES);
+    callProviderAISimple.mockResolvedValue({ error: 'Provider returned an empty completion' });
+  });
+
+  it('generateThemeAnalysis surfaces the error and does not write themes.json', async () => {
+    const result = await generateThemeAnalysis();
+
+    expect(callProviderAISimple).toHaveBeenCalledTimes(1);
+    expect(result).toEqual({ available: false, reason: 'Provider returned an empty completion' });
+    expect(atomicWrite).not.toHaveBeenCalled();
+  });
+
+  it('refreshCrossDomainNarrative surfaces the error and does not write narrative.json', async () => {
+    const result = await refreshCrossDomainNarrative();
+
+    expect(callProviderAISimple).toHaveBeenCalledTimes(1);
+    expect(result).toEqual({ available: false, reason: 'Provider returned an empty completion' });
+    expect(atomicWrite).not.toHaveBeenCalled();
+  });
+
+  it('generateThemeAnalysis writes themes.json on a usable completion', async () => {
+    callProviderAISimple.mockResolvedValue({ text: '[{"title":"New theme","strength":"strong"}]' });
+
+    const result = await generateThemeAnalysis();
+
+    expect(atomicWrite).toHaveBeenCalledTimes(1);
+    expect(atomicWrite.mock.calls[0][1]).toMatchObject({
+      themes: [{ title: 'New theme', strength: 'strong' }],
+    });
+    expect(result.themes).toHaveLength(1);
+  });
+});