Return copies of cached models list and improve test robustness

Co-authored-by: friggeri <106686+friggeri@users.noreply.github.com>

Author: Copilot

python/copilot/client.py

@@ -737,7 +737,7 @@ async def list_models(self) -> list["ModelInfo"]:
         async with self._models_cache_lock:
             # Check cache (already inside lock)
             if self._models_cache is not None:
-                return self._models_cache
+                return list(self._models_cache)  # Return a copy to prevent cache mutation
 
             # Cache miss - fetch from backend while holding lock
             response = await self._client.request("models.list", {})
@@ -747,7 +747,7 @@ async def list_models(self) -> list["ModelInfo"]:
             # Update cache before releasing lock
             self._models_cache = models
 
-            return models
+            return list(models)  # Return a copy to prevent cache mutation
 
     async def list_sessions(self) -> list["SessionMetadata"]:
         """

python/e2e/test_client.py

@@ -154,15 +154,25 @@ async def test_should_cache_models_list(self):
             models1 = await client.list_models()
             assert isinstance(models1, list)
 
-            # Second call should return cached results (same object reference)
+            # Second call should return from cache (different list object but same content)
             models2 = await client.list_models()
-            assert models2 is models1, "Second call should return cached results"
+            assert models2 is not models1, "Should return a copy, not the same object"
+            assert len(models2) == len(models1), "Cached results should have same content"
+            if len(models1) > 0:
+                assert models1[0].id == models2[0].id, "Cached models should match"
 
             # After stopping, cache should be cleared
             await client.stop()
 
             # Restart and verify cache is empty
             await client.start()
+
+            # Check authentication again after restart
+            auth_status = await client.get_auth_status()
+            if not auth_status.isAuthenticated:
+                await client.stop()
+                return
+
             models3 = await client.list_models()
             assert models3 is not models1, "Cache should be cleared after disconnect"