fix(fallback): merge fallback_providers with legacy fallback_model configurations

tests/cli/test_cli_init.py

@@ -102,6 +102,20 @@ class TestVerboseAndToolProgress:
         assert cli.tool_progress_mode in {"off", "new", "all", "verbose"}
 
 
+class TestFallbackChainInit:
+    def test_merges_new_and_legacy_fallback_config(self):
+        cli = _make_cli(config_overrides={
+            "fallback_providers": [
+                {"provider": "openrouter", "model": "anthropic/claude-sonnet-4.6"},
+            ],
+            "fallback_model": {"provider": "nous", "model": "Hermes-4"},
+        })
+        assert cli._fallback_model == [
+            {"provider": "openrouter", "model": "anthropic/claude-sonnet-4.6"},
+            {"provider": "nous", "model": "Hermes-4"},
+        ]
+
+
 class TestBusyInputMode:
     def test_default_busy_input_mode_is_interrupt(self):
         cli = _make_cli()