D2: verify GET /api/jobs returns error field for failed jobs

Verification tests for outcome-contract clause
failed-job-error-exposed-for-ui-banner.

- db.test.ts: listJobs includes error for failed jobs, null for non-failed
- jobs-list-endpoint.test.ts: route-level integration with real DB,
  exercises GET handler end-to-end

D2 already merged (f03b757+); non-blocking verification only.

src/tests/db.test.ts

@@ -174,6 +174,24 @@ describe('listJobs', () => {
 	it('returns an array (possibly empty)', () => {
 		expect(Array.isArray(listJobs())).toBe(true);
 	});
+
+	it('includes error field for failed jobs — D2 error banner data contract', () => {
+		const job = createJob('src', 'Failed Job', 'auto');
+		updateJob({ id: job.id, status: 'failed', error: 'simulated transcription failure for outcome-contract probe' });
+		const jobs = listJobs();
+		const found = jobs.find((j) => j.id === job.id);
+		expect(found).toBeDefined();
+		expect(found!.error).toBe('simulated transcription failure for outcome-contract probe');
+	});
+
+	it('returns null error for non-failed jobs', () => {
+		const job = createJob('src', 'Done Job', 'auto');
+		updateJob({ id: job.id, status: 'done', error: null });
+		const jobs = listJobs();
+		const found = jobs.find((j) => j.id === job.id);
+		expect(found).toBeDefined();
+		expect(found!.error).toBeNull();
+	});
 });
 
 // ── Push subscriptions ────────────────────────────────────────────────────────

src/tests/jobs-list-endpoint.test.ts

@@ -0,0 +1,81 @@
+import { describe, it, expect, afterAll, vi } from 'vitest';
+import { join } from 'path';
+import { tmpdir } from 'os';
+import { rm } from 'fs/promises';
+
+/**
+ * Integration test for GET /api/jobs — verifies the error field is
+ * exposed for failed jobs and null for non-failed jobs, exercising
+ * the full db→API path with a real SQLite database.
+ *
+ * Covers outcome-contract clause failed-job-error-exposed-for-ui-banner.
+ * D2 already merged (f03b757+); this is non-blocking verification.
+ */
+
+const TEST_DATA_DIR = join(tmpdir(), 'whisper-pwa-jobs-list-int-' + process.pid);
+vi.stubEnv('DATA_DIR', TEST_DATA_DIR);
+
+const { createJob, getJob, updateJob, listJobs } = await import('$lib/server/db.js');
+const { GET } = await import('$lib/../routes/api/jobs/+server.js');
+
+afterAll(async () => {
+	await rm(TEST_DATA_DIR, { recursive: true, force: true });
+});
+
+describe('GET /api/jobs — error field exposure', () => {
+	it('includes error field for a failed job', async () => {
+		const job = createJob('probe-upload.webm', 'UI error probe', 'auto');
+		updateJob({
+			id: job.id,
+			status: 'failed',
+			error: 'simulated transcription failure for outcome-contract probe'
+		});
+
+		const res = await GET();
+		expect(res.status).toBe(200);
+		const body = await res.json();
+		expect(Array.isArray(body)).toBe(true);
+
+		const found = body.find((j: any) => j.id === job.id);
+		expect(found).toBeDefined();
+		expect(found.status).toBe('failed');
+		expect(found.error).toBe('simulated transcription failure for outcome-contract probe');
+	});
+
+	it('returns null error for a non-failed job', async () => {
+		const job = createJob('probe-done.webm', 'Done probe', 'auto');
+		updateJob({ id: job.id, status: 'done', error: null });
+
+		const res = await GET();
+		expect(res.status).toBe(200);
+		const body = await res.json();
+
+		const found = body.find((j: any) => j.id === job.id);
+		expect(found).toBeDefined();
+		expect(found.error).toBeNull();
+	});
+
+	it('preserves other job fields when error is present', async () => {
+		const job = createJob('my-recording.webm', 'My Recording', 'aggressive');
+		updateJob({
+			id: job.id,
+			status: 'failed',
+			error: 'transcription failed',
+			progress: 50,
+			whisperJobId: 'whisper-123'
+		});
+
+		const res = await GET();
+		const body = await res.json();
+		const found = body.find((j: any) => j.id === job.id);
+
+		expect(found).toBeDefined();
+		expect(found.status).toBe('failed');
+		expect(found.error).toBe('transcription failed');
+		expect(found.title).toBe('My Recording');
+		expect(found.source).toBe('my-recording.webm');
+		expect(found.audioMode).toBe('aggressive');
+		expect(found.progress).toBe(50);
+		expect(found.whisperJobId).toBe('whisper-123');
+	});
+});