diff --git a/apps/api/src/jobs/worker.ts b/apps/api/src/jobs/worker.ts
index bc562c92..270a7156 100644
--- a/apps/api/src/jobs/worker.ts
+++ b/apps/api/src/jobs/worker.ts
@@ -369,7 +369,7 @@ async function processToolJob(job: Job<ToolJobData>): Promise<ToolJobResult> {
       const finalError = isCanceled
         ? "Canceled"
         : isTimeout
-          ? `Timed out after ${Math.round(timeoutMs / 1000)}s`
+          ? `Timed out after ${Math.round(timeoutMs / 1000)}s. On the first run the background-removal model may still be downloading; the image may be too large for CPU inference; or the worker may be busy or unavailable. Retry once the model has downloaded, or try a smaller image.`
           : errorMessage;
 
       // Log genuine processing faults at error level (clients only ever see
diff --git a/tests/integration/platform/worker-timeout.test.ts b/tests/integration/platform/worker-timeout.test.ts
index d4c50ee2..c89415e0 100644
--- a/tests/integration/platform/worker-timeout.test.ts
+++ b/tests/integration/platform/worker-timeout.test.ts
@@ -116,6 +116,10 @@ describe("Worker timeout classification", () => {
     // Error message must mention timeout
     const error = finalRow?.error as { message: string };
     expect(error.message).toMatch(/timed out after 1s/i);
+    // Fail-fast message must include actionable guidance (issue #494)
+    expect(error.message).toMatch(
+      /model may still be downloading|too large for CPU|worker may be busy/i,
+    );
 
     // Both attempts ran (attempts column is set at the start of each attempt)
     expect(finalRow?.attempts).toBe(2);