D3: wire health preflight into pipeline before whisper submission

Add health preflight check in runJob() after ensureWhisperRunning()
and before submitJob(). Uses existing getHealth() from whisper.ts
with retryWithBackoff() for transient failures.

- Healthy whisper (status 'ok') -> job proceeds to submission
- Unreachable whisper -> job fails early with 'whisper health check failed: ...'
- Non-ok status (e.g. 'starting') -> job fails early with actual status
- getHealth() 5000ms timeout preserved, no new HTTP client

Tests: health-preflight.test.ts covers error message contracts
and pipeline integration (YouTube + upload source)

src/lib/server/pipeline.ts

@@ -1,8 +1,9 @@
 import { createJob, updateJob, setJobStatus, getJob, resetJob } from './db.js';
 import { downloadYouTube, saveUploadedFile, cleanupJobTmp, getUploadPath, cleanupUploadDir } from './downloader.js';
 import { prepareAudio, cleanup as cleanupFiles } from './audio.js';
-import { submitJob, streamJob } from './whisper.js';
+import { submitJob, streamJob, getHealth } from './whisper.js';
 import { ensureWhisperRunning } from './docker.js';
+import { retryWithBackoff } from './retry.js';
 import type { AudioMode, Segment } from '$lib/types.js';
 
 const WEBHOOK_BASE_URL = process.env.WEBHOOK_BASE_URL ?? 'http://localhost:3000';
@@ -151,6 +152,31 @@ async function runJob(
 		// ── 3. Ensure whisper is running ──────────────────────────────────────
 		await ensureWhisperRunning();
 
+		// ── 3b. Health preflight: verify whisper reachability and status ──────
+		await retryWithBackoff(
+			async () => {
+				try {
+					const health = await getHealth();
+					if (health.status !== 'ok') {
+						throw new Error(`whisper health check failed: status is "${health.status}"`);
+					}
+				} catch (err) {
+					if (err instanceof Error && err.message.startsWith('whisper health check failed')) {
+						throw err;
+					}
+					throw new Error(`whisper health check failed: ${err instanceof Error ? err.message : String(err)}`);
+				}
+			},
+			{
+				maxAttempts: 3,
+				baseDelayMs: 1000,
+				onAttempt: (err, attempt, delayMs) => {
+					console.warn(`[pipeline] whisper health check attempt ${attempt} failed:`, err);
+					emitProgress(jobId, { type: 'warning', message: `health check attempt ${attempt} failed, retrying in ${delayMs}ms` });
+				}
+			}
+		);
+
 		// ── 4. Submit to whisper with webhook ────────────────────────────────
 		setJobStatus(jobId, 'transcribing', 10);
 		emitProgress(jobId, { type: 'status', status: 'transcribing', progress: 10 });