diff --git a/apps/server/src/integrations/ai/ai-http.spec.ts b/apps/server/src/integrations/ai/ai-http.spec.ts
index 044c18f9..4fbfab04 100644
--- a/apps/server/src/integrations/ai/ai-http.spec.ts
+++ b/apps/server/src/integrations/ai/ai-http.spec.ts
@@ -1,5 +1,10 @@
+import * as http from 'node:http';
 import { RetryAgent } from 'undici';
 
+// A short header timeout makes the #140 "header stall" deterministic and fast.
+// Must be set BEFORE importing ai-http (the undici agents read it at module load).
+process.env.AI_HTTP_HEADERS_TIMEOUT_MS = '800';
+
 import { aiFetch } from './ai-http';
 
 /**
@@ -45,3 +50,63 @@ describe('ai-http', () => {
     }
   });
 });
+
+/**
+ * #140 regression: a provider that accepts the request but stalls without ever
+ * sending response headers must FAIL FAST (at headersTimeout — set to 800ms
+ * above, not undici's 300s default) and be RETRIED on a fresh connection.
+ * headersTimeout only bounds time-to-headers, so a healthy fast response is
+ * unaffected. Uses a real loopback server; makes no external network calls.
+ */
+describe('aiFetch header-stall resilience (#140)', () => {
+  function makeServer(
+    handler: http.RequestListener,
+  ): Promise<{ url: string; close: () => Promise<void> }> {
+    return new Promise((resolve) => {
+      const server = http.createServer(handler);
+      server.listen(0, '127.0.0.1', () => {
+        const port = (server.address() as { port: number }).port;
+        resolve({
+          url: `http://127.0.0.1:${port}/health`,
+          close: () => new Promise<void>((r) => server.close(() => r())),
+        });
+      });
+    });
+  }
+
+  it('retries a header stall on a fresh connection and recovers', async () => {
+    let attempts = 0;
+    const { url, close } = await makeServer((_req, res) => {
+      attempts++;
+      // First attempt: never send headers -> UND_ERR_HEADERS_TIMEOUT -> retry.
+      if (attempts === 1) return;
+      res.writeHead(200, { 'content-type': 'application/json' });
+      res.end(JSON.stringify({ ok: true, servedOnAttempt: attempts }));
+    });
+    try {
+      const res = await aiFetch(url, { method: 'GET' });
+      expect(res.status).toBe(200);
+      const body = (await res.json()) as { servedOnAttempt: number };
+      expect(attempts).toBeGreaterThanOrEqual(2); // the stalled attempt was retried
+      expect(body.servedOnAttempt).toBeGreaterThanOrEqual(2);
+    } finally {
+      await close();
+    }
+  }, 15000);
+
+  it('passes a healthy fast response straight through (one attempt)', async () => {
+    let attempts = 0;
+    const { url, close } = await makeServer((_req, res) => {
+      attempts++;
+      res.writeHead(200, { 'content-type': 'application/json' });
+      res.end(JSON.stringify({ ok: true }));
+    });
+    try {
+      const res = await aiFetch(url, { method: 'GET' });
+      expect(res.status).toBe(200);
+      expect(attempts).toBe(1);
+    } finally {
+      await close();
+    }
+  }, 15000);
+});