fix: use configured model for gateway auth fallback

gateway/run.py

@@ -643,7 +643,11 @@ def _try_resolve_fallback_provider() -> dict | None:
                     explicit_base_url=entry.get("base_url"),
                     explicit_api_key=entry.get("api_key"),
                 )
-                logger.info("Fallback provider resolved: %s", runtime.get("provider"))
+                logger.info(
+                    "Fallback provider resolved: %s model=%s",
+                    runtime.get("provider"),
+                    entry.get("model"),
+                )
                 return {
                     "api_key": runtime.get("api_key"),
                     "base_url": runtime.get("base_url"),
@@ -652,6 +656,7 @@ def _try_resolve_fallback_provider() -> dict | None:
                     "command": runtime.get("command"),
                     "args": list(runtime.get("args") or []),
                     "credential_pool": runtime.get("credential_pool"),
+                    "model": entry.get("model"),
                 }
             except Exception as fb_exc:
                 logger.debug("Fallback entry %s failed: %s", entry.get("provider"), fb_exc)
@@ -1661,6 +1666,14 @@ class GatewayRunner:
             )
 
         runtime_kwargs = _resolve_runtime_agent_kwargs()
+        runtime_model = runtime_kwargs.pop("model", None)
+        if runtime_model:
+            logger.info(
+                "Runtime provider supplied explicit model override: %s -> %s",
+                model,
+                runtime_model,
+            )
+            model = runtime_model
         if override and resolved_session_key:
             model, runtime_kwargs = self._apply_session_model_override(
                 resolved_session_key, model, runtime_kwargs

tests/gateway/test_session_model_override_routing.py

@@ -163,3 +163,58 @@ async def test_background_task_prefers_session_override_over_global_runtime(monk
     assert _CapturingAgent.last_init["base_url"] == "https://chatgpt.com/backend-api/codex"
     assert _CapturingAgent.last_init["api_key"] == "***"
     assert _CapturingAgent.last_init["reasoning_config"] == {"enabled": True, "effort": "high"}
+
+def test_gateway_auth_fallback_uses_fallback_model_from_config(tmp_path, monkeypatch):
+    """Regression: fallback provider must not inherit the primary model.
+
+    If primary openai-codex auth fails and fallback_providers selects
+    OpenRouter/minimax, the gateway must instantiate AIAgent with the fallback
+    model, not the primary config model (e.g. gpt-5.5). Otherwise OpenRouter
+    receives an unintended GPT request.
+    """
+    config = tmp_path / "config.yaml"
+    config.write_text(
+        """
+model:
+  default: gpt-5.5
+  provider: openai-codex
+fallback_providers:
+  - provider: openrouter
+    model: minimax/minimax-m2.7
+""".lstrip(),
+        encoding="utf-8",
+    )
+    monkeypatch.setattr(gateway_run, "_hermes_home", tmp_path)
+
+    def fake_resolve_runtime_provider(*, requested=None, explicit_base_url=None, explicit_api_key=None):
+        if requested in (None, "", "openai-codex"):
+            from hermes_cli.auth import AuthError
+            raise AuthError("No Codex credentials stored. Run `hermes auth` to authenticate.")
+        assert requested == "openrouter"
+        return {
+            "api_key": "sk-openrouter",
+            "base_url": "https://openrouter.ai/api/v1",
+            "provider": "openrouter",
+            "api_mode": "chat_completions",
+            "command": None,
+            "args": [],
+            "credential_pool": None,
+        }
+
+    import hermes_cli.runtime_provider as runtime_provider
+
+    monkeypatch.setattr(runtime_provider, "resolve_runtime_provider", fake_resolve_runtime_provider)
+
+    runner = _make_runner()
+    model, runtime_kwargs = runner._resolve_session_agent_runtime(
+        session_key="agent:main:telegram:group:-1003715515980:63",
+        user_config={
+            "model": {"default": "gpt-5.5", "provider": "openai-codex"},
+            "fallback_providers": [{"provider": "openrouter", "model": "minimax/minimax-m2.7"}],
+        },
+    )
+
+    assert model == "minimax/minimax-m2.7"
+    assert runtime_kwargs["provider"] == "openrouter"
+    assert runtime_kwargs["api_key"] == "sk-openrouter"
+