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()

tests/gateway/test_auth_fallback.py

@@ -71,3 +71,46 @@ class TestResolveRuntimeAgentKwargsAuthFallback:
             from gateway.run import _resolve_runtime_agent_kwargs
             with pytest.raises(RuntimeError):
                 _resolve_runtime_agent_kwargs()
+
+    def test_legacy_fallback_is_appended_after_fallback_providers(self, tmp_path, monkeypatch):
+        """When both keys exist, the legacy entry still participates in resolution."""
+        config_path = tmp_path / "config.yaml"
+        config_path.write_text(
+            "fallback_providers:\n"
+            "  - provider: openrouter\n"
+            "    model: anthropic/claude-sonnet-4.6\n"
+            "fallback_model:\n"
+            "  provider: nous\n"
+            "  model: Hermes-4\n"
+        )
+
+        monkeypatch.setattr("gateway.run._hermes_home", tmp_path)
+
+        calls = []
+
+        def _mock_resolve(**kwargs):
+            requested = kwargs.get("requested")
+            calls.append(requested)
+            if requested == "openrouter":
+                raise RuntimeError("openrouter unavailable")
+            return {
+                "api_key": "nous-key",
+                "base_url": "https://portal.nousresearch.com/v1",
+                "provider": "nous",
+                "api_mode": "chat_completions",
+                "command": None,
+                "args": None,
+                "credential_pool": None,
+            }
+
+        with patch(
+            "hermes_cli.runtime_provider.resolve_runtime_provider",
+            side_effect=_mock_resolve,
+        ):
+            from gateway.run import _try_resolve_fallback_provider
+
+            result = _try_resolve_fallback_provider()
+
+        assert calls == ["openrouter", "nous"]
+        assert result["provider"] == "nous"
+        assert result["model"] == "Hermes-4"

tests/hermes_cli/test_fallback_cmd.py

@@ -55,6 +55,31 @@ class TestReadChain:
             {"provider": "nous", "model": "Hermes-4-Llama-3.1-405B"},
         ]
 
+    def test_merges_new_and_legacy_formats(self):
+        from hermes_cli.fallback_cmd import _read_chain
+        cfg = {
+            "fallback_providers": [
+                {"provider": "openrouter", "model": "anthropic/claude-sonnet-4.6"},
+            ],
+            "fallback_model": {"provider": "nous", "model": "Hermes-4"},
+        }
+        assert _read_chain(cfg) == [
+            {"provider": "openrouter", "model": "anthropic/claude-sonnet-4.6"},
+            {"provider": "nous", "model": "Hermes-4"},
+        ]
+
+    def test_legacy_duplicate_is_deduplicated_after_merge(self):
+        from hermes_cli.fallback_cmd import _read_chain
+        cfg = {
+            "fallback_providers": [
+                {"provider": "openrouter", "model": "anthropic/claude-sonnet-4.6"},
+            ],
+            "fallback_model": {"provider": "OpenRouter", "model": "anthropic/claude-sonnet-4.6"},
+        }
+        assert _read_chain(cfg) == [
+            {"provider": "openrouter", "model": "anthropic/claude-sonnet-4.6"},
+        ]
+
     def test_migrates_legacy_single_dict(self):
         from hermes_cli.fallback_cmd import _read_chain
         cfg = {"fallback_model": {"provider": "openrouter", "model": "gpt-5.4"}}