fix: abort model retries immediately on user cancellation

src/models/router.test.ts

@@ -476,6 +476,38 @@ describe('setClient and labels', () => {
     expect(router.isTierStrict('default')).toBe(true);
   });
 
+  it('requestAbort interrupts retry loop before fallback chain', async () => {
+    const primary = {
+      chat: vi.fn().mockRejectedValue(new Error('temporary failure')),
+    } as unknown as ModelClient;
+    const fallback = {
+      chat: vi.fn().mockResolvedValue({
+        content: 'fallback',
+        stopReason: 'end_turn',
+        usage: { inputTokens: 1, outputTokens: 1 },
+      }),
+    } as unknown as ModelClient;
+
+    const router = new ModelRouter({
+      default: primary,
+      fallbackChain: [fallback],
+      retryConfig: {
+        maxRetries: 3,
+        initialDelayMs: 80,
+        backoffMultiplier: 1,
+        maxDelayMs: 80,
+        nonRetryablePatterns: [],
+      },
+    });
+
+    const run = router.chat({ messages: [{ role: 'user', content: 'hi' }] });
+    setTimeout(() => router.requestAbort(), 10);
+
+    await expect(run).rejects.toMatchObject({ name: 'AbortError' });
+    expect(primary.chat).toHaveBeenCalledTimes(1);
+    expect(fallback.chat).not.toHaveBeenCalled();
+  });
+
   it('setOnTierChange does not replace existing listeners', () => {
     const router = new ModelRouter({
       default: { chat: vi.fn() } as unknown as ModelClient,