diff --git a/agent/auxiliary_client.py b/agent/auxiliary_client.py
index 04afe4c78..19c2b8bd9 100644
--- a/agent/auxiliary_client.py
+++ b/agent/auxiliary_client.py
@@ -536,6 +536,7 @@ def resolve_provider_client(
     provider: str,
     model: str = None,
     async_mode: bool = False,
+    raw_codex: bool = False,
 ) -> Tuple[Optional[Any], Optional[str]]:
     """Central router: given a provider name and optional model, return a
     configured client with the correct auth, base URL, and API format.
@@ -553,6 +554,10 @@ def resolve_provider_client(
         model: Model slug override.  If None, uses the provider's default
                auxiliary model.
         async_mode: If True, return an async-compatible client.
+        raw_codex: If True, return a raw OpenAI client for Codex providers
+            instead of wrapping in CodexAuxiliaryClient.  Use this when
+            the caller needs direct access to responses.stream() (e.g.,
+            the main agent loop).
 
     Returns:
         (client, resolved_model) or (None, None) if auth is unavailable.
@@ -597,6 +602,18 @@ def resolve_provider_client(
 
     # ── OpenAI Codex (OAuth → Responses API) ─────────────────────────
     if provider == "openai-codex":
+        if raw_codex:
+            # Return the raw OpenAI client for callers that need direct
+            # access to responses.stream() (e.g., the main agent loop).
+            codex_token = _read_codex_access_token()
+            if not codex_token:
+                logger.warning("resolve_provider_client: openai-codex requested "
+                               "but no Codex OAuth token found (run: hermes model)")
+                return None, None
+            final_model = model or _CODEX_AUX_MODEL
+            raw_client = OpenAI(api_key=codex_token, base_url=_CODEX_AUX_BASE_URL)
+            return (raw_client, final_model)
+        # Standard path: wrap in CodexAuxiliaryClient adapter
         client, default = _try_codex()
         if client is None:
             logger.warning("resolve_provider_client: openai-codex requested "
diff --git a/run_agent.py b/run_agent.py
index 8849d25c3..107b803c6 100644
--- a/run_agent.py
+++ b/run_agent.py
@@ -418,36 +418,50 @@ class AIAgent:
                 ]:
                     logging.getLogger(quiet_logger).setLevel(logging.ERROR)
         
-        # Initialize OpenAI client - defaults to OpenRouter
-        client_kwargs = {}
-        
-        # Default to OpenRouter if no base_url provided
-        if base_url:
-            client_kwargs["base_url"] = base_url
+        # Initialize OpenAI client via centralized provider router.
+        # The router handles auth resolution, base URL, headers, and
+        # Codex wrapping for all known providers.
+        # raw_codex=True because the main agent needs direct responses.stream()
+        # access for Codex Responses API streaming.
+        if api_key and base_url:
+            # Explicit credentials from CLI/gateway — construct directly.
+            # The runtime provider resolver already handled auth for us.
+            client_kwargs = {"api_key": api_key, "base_url": base_url}
+            effective_base = base_url
+            if "openrouter" in effective_base.lower():
+                client_kwargs["default_headers"] = {
+                    "HTTP-Referer": "https://github.com/NousResearch/hermes-agent",
+                    "X-OpenRouter-Title": "Hermes Agent",
+                    "X-OpenRouter-Categories": "productivity,cli-agent",
+                }
+            elif "api.kimi.com" in effective_base.lower():
+                client_kwargs["default_headers"] = {
+                    "User-Agent": "KimiCLI/1.0",
+                }
         else:
-            client_kwargs["base_url"] = OPENROUTER_BASE_URL
-        
-        # Handle API key - OpenRouter is the primary provider
-        if api_key:
-            client_kwargs["api_key"] = api_key
-        else:
-            # Primary: OPENROUTER_API_KEY, fallback to direct provider keys
-            client_kwargs["api_key"] = os.getenv("OPENROUTER_API_KEY", "")
-        
-        # OpenRouter app attribution — shows hermes-agent in rankings/analytics
-        effective_base = client_kwargs.get("base_url", "")
-        if "openrouter" in effective_base.lower():
-            client_kwargs["default_headers"] = {
-                "HTTP-Referer": "https://github.com/NousResearch/hermes-agent",
-                "X-OpenRouter-Title": "Hermes Agent",
-                "X-OpenRouter-Categories": "productivity,cli-agent",
-            }
-        elif "api.kimi.com" in effective_base.lower():
-            # Kimi Code API requires a recognized coding-agent User-Agent
-            # (see https://github.com/MoonshotAI/kimi-cli)
-            client_kwargs["default_headers"] = {
-                "User-Agent": "KimiCLI/1.0",
-            }
+            # No explicit creds — use the centralized provider router
+            from agent.auxiliary_client import resolve_provider_client
+            _routed_client, _ = resolve_provider_client(
+                self.provider or "auto", model=self.model, raw_codex=True)
+            if _routed_client is not None:
+                client_kwargs = {
+                    "api_key": _routed_client.api_key,
+                    "base_url": str(_routed_client.base_url),
+                }
+                # Preserve any default_headers the router set
+                if hasattr(_routed_client, '_default_headers') and _routed_client._default_headers:
+                    client_kwargs["default_headers"] = dict(_routed_client._default_headers)
+            else:
+                # Final fallback: try raw OpenRouter key
+                client_kwargs = {
+                    "api_key": os.getenv("OPENROUTER_API_KEY", ""),
+                    "base_url": OPENROUTER_BASE_URL,
+                    "default_headers": {
+                        "HTTP-Referer": "https://github.com/NousResearch/hermes-agent",
+                        "X-OpenRouter-Title": "Hermes Agent",
+                        "X-OpenRouter-Categories": "productivity,cli-agent",
+                    },
+                }
         
         self._client_kwargs = client_kwargs  # stored for rebuilding after interrupt
         try:
@@ -2236,75 +2250,6 @@ class AIAgent:
 
     # ── Provider fallback ──────────────────────────────────────────────────
 
-    # API-key providers: provider → (base_url, [env_var_names])
-    _FALLBACK_API_KEY_PROVIDERS = {
-        "openrouter": (OPENROUTER_BASE_URL, ["OPENROUTER_API_KEY"]),
-        "zai": ("https://api.z.ai/api/paas/v4", ["ZAI_API_KEY", "Z_AI_API_KEY"]),
-        "kimi-coding": ("https://api.moonshot.ai/v1", ["KIMI_API_KEY"]),
-        "minimax": ("https://api.minimax.io/v1", ["MINIMAX_API_KEY"]),
-        "minimax-cn": ("https://api.minimaxi.com/v1", ["MINIMAX_CN_API_KEY"]),
-    }
-
-    # OAuth providers: provider → (resolver_import_path, api_mode)
-    # Each resolver returns {"api_key": ..., "base_url": ...}.
-    _FALLBACK_OAUTH_PROVIDERS = {
-        "openai-codex": ("resolve_codex_runtime_credentials", "codex_responses"),
-        "nous": ("resolve_nous_runtime_credentials", "chat_completions"),
-    }
-
-    def _resolve_fallback_credentials(
-        self, fb_provider: str, fb_config: dict
-    ) -> Optional[tuple]:
-        """Resolve credentials for a fallback provider.
-
-        Returns (api_key, base_url, api_mode) on success, or None on failure.
-        Handles three cases:
-          1. OAuth providers (openai-codex, nous) — call credential resolver
-          2. API-key providers (openrouter, zai, etc.) — read env var
-          3. Custom endpoints — use base_url + api_key_env from config
-        """
-        # ── 1. OAuth providers ────────────────────────────────────────
-        if fb_provider in self._FALLBACK_OAUTH_PROVIDERS:
-            resolver_name, api_mode = self._FALLBACK_OAUTH_PROVIDERS[fb_provider]
-            try:
-                import hermes_cli.auth as _auth
-                resolver = getattr(_auth, resolver_name)
-                creds = resolver()
-                return creds["api_key"], creds["base_url"], api_mode
-            except Exception as e:
-                logging.warning(
-                    "Fallback to %s failed (credential resolution): %s",
-                    fb_provider, e,
-                )
-                return None
-
-        # ── 2. API-key providers ──────────────────────────────────────
-        fb_key = (fb_config.get("api_key") or "").strip()
-        if not fb_key:
-            key_env = (fb_config.get("api_key_env") or "").strip()
-            if key_env:
-                fb_key = os.getenv(key_env, "")
-            elif fb_provider in self._FALLBACK_API_KEY_PROVIDERS:
-                for env_var in self._FALLBACK_API_KEY_PROVIDERS[fb_provider][1]:
-                    fb_key = os.getenv(env_var, "")
-                    if fb_key:
-                        break
-        if not fb_key:
-            logging.warning(
-                "Fallback model configured but no API key found for provider '%s'",
-                fb_provider,
-            )
-            return None
-
-        # ── 3. Resolve base URL ───────────────────────────────────────
-        fb_base_url = (fb_config.get("base_url") or "").strip()
-        if not fb_base_url and fb_provider in self._FALLBACK_API_KEY_PROVIDERS:
-            fb_base_url = self._FALLBACK_API_KEY_PROVIDERS[fb_provider][0]
-        if not fb_base_url:
-            fb_base_url = OPENROUTER_BASE_URL
-
-        return fb_key, fb_base_url, "chat_completions"
-
     def _try_activate_fallback(self) -> bool:
         """Switch to the configured fallback model/provider.
 
@@ -2312,6 +2257,10 @@ class AIAgent:
         OpenAI client, model slug, and provider in-place so the retry loop
         can continue with the new backend.  One-shot: returns False if
         already activated or not configured.
+
+        Uses the centralized provider router (resolve_provider_client) for
+        auth resolution and client construction — no duplicated provider→key
+        mappings.
         """
         if self._fallback_activated or not self._fallback_model:
             return False
@@ -2322,25 +2271,31 @@ class AIAgent:
         if not fb_provider or not fb_model:
             return False
 
-        resolved = self._resolve_fallback_credentials(fb_provider, fb)
-        if resolved is None:
-            return False
-        fb_key, fb_base_url, fb_api_mode = resolved
-
-        # Build new client
+        # Use centralized router for client construction.
+        # raw_codex=True because the main agent needs direct responses.stream()
+        # access for Codex providers.
         try:
-            client_kwargs = {"api_key": fb_key, "base_url": fb_base_url}
-            if "openrouter" in fb_base_url.lower():
-                client_kwargs["default_headers"] = {
-                    "HTTP-Referer": "https://github.com/NousResearch/hermes-agent",
-                    "X-OpenRouter-Title": "Hermes Agent",
-                    "X-OpenRouter-Categories": "productivity,cli-agent",
-                }
-            elif "api.kimi.com" in fb_base_url.lower():
-                client_kwargs["default_headers"] = {"User-Agent": "KimiCLI/1.0"}
+            from agent.auxiliary_client import resolve_provider_client
+            fb_client, _ = resolve_provider_client(
+                fb_provider, model=fb_model, raw_codex=True)
+            if fb_client is None:
+                logging.warning(
+                    "Fallback to %s failed: provider not configured",
+                    fb_provider)
+                return False
 
-            self.client = OpenAI(**client_kwargs)
-            self._client_kwargs = client_kwargs
+            # Determine api_mode from provider
+            fb_api_mode = "chat_completions"
+            if fb_provider == "openai-codex":
+                fb_api_mode = "codex_responses"
+            fb_base_url = str(fb_client.base_url)
+
+            # Swap client and config in-place
+            self.client = fb_client
+            self._client_kwargs = {
+                "api_key": fb_client.api_key,
+                "base_url": fb_base_url,
+            }
             old_model = self.model
             self.model = fb_model
             self.provider = fb_provider
diff --git a/tests/test_fallback_model.py b/tests/test_fallback_model.py
index dcc150c37..9e34bf749 100644
--- a/tests/test_fallback_model.py
+++ b/tests/test_fallback_model.py
@@ -35,7 +35,7 @@ def _make_agent(fallback_model=None):
         patch("run_agent.OpenAI"),
     ):
         agent = AIAgent(
-            api_key="test-key-primary",
+            api_key="test-key",
             quiet_mode=True,
             skip_context_files=True,
             skip_memory=True,
@@ -45,6 +45,14 @@ def _make_agent(fallback_model=None):
         return agent
 
 
+def _mock_resolve(base_url="https://openrouter.ai/api/v1", api_key="test-key"):
+    """Helper to create a mock client for resolve_provider_client."""
+    mock_client = MagicMock()
+    mock_client.api_key = api_key
+    mock_client.base_url = base_url
+    return mock_client
+
+
 # =============================================================================
 # _try_activate_fallback()
 # =============================================================================
@@ -71,9 +79,13 @@ class TestTryActivateFallback:
         agent = _make_agent(
             fallback_model={"provider": "openrouter", "model": "anthropic/claude-sonnet-4"},
         )
-        with (
-            patch.dict("os.environ", {"OPENROUTER_API_KEY": "sk-or-fallback-key"}),
-            patch("run_agent.OpenAI") as mock_openai,
+        mock_client = _mock_resolve(
+            api_key="sk-or-fallback-key",
+            base_url="https://openrouter.ai/api/v1",
+        )
+        with patch(
+            "agent.auxiliary_client.resolve_provider_client",
+            return_value=(mock_client, "anthropic/claude-sonnet-4"),
         ):
             result = agent._try_activate_fallback()
             assert result is True
@@ -81,36 +93,37 @@ class TestTryActivateFallback:
             assert agent.model == "anthropic/claude-sonnet-4"
             assert agent.provider == "openrouter"
             assert agent.api_mode == "chat_completions"
-            mock_openai.assert_called_once()
-            call_kwargs = mock_openai.call_args[1]
-            assert call_kwargs["api_key"] == "sk-or-fallback-key"
-            assert "openrouter" in call_kwargs["base_url"].lower()
-            # OpenRouter should get attribution headers
-            assert "default_headers" in call_kwargs
+            assert agent.client is mock_client
 
     def test_activates_zai_fallback(self):
         agent = _make_agent(
             fallback_model={"provider": "zai", "model": "glm-5"},
         )
-        with (
-            patch.dict("os.environ", {"ZAI_API_KEY": "sk-zai-key"}),
-            patch("run_agent.OpenAI") as mock_openai,
+        mock_client = _mock_resolve(
+            api_key="sk-zai-key",
+            base_url="https://open.z.ai/api/v1",
+        )
+        with patch(
+            "agent.auxiliary_client.resolve_provider_client",
+            return_value=(mock_client, "glm-5"),
         ):
             result = agent._try_activate_fallback()
             assert result is True
             assert agent.model == "glm-5"
             assert agent.provider == "zai"
-            call_kwargs = mock_openai.call_args[1]
-            assert call_kwargs["api_key"] == "sk-zai-key"
-            assert "z.ai" in call_kwargs["base_url"].lower()
+            assert agent.client is mock_client
 
     def test_activates_kimi_fallback(self):
         agent = _make_agent(
             fallback_model={"provider": "kimi-coding", "model": "kimi-k2.5"},
         )
-        with (
-            patch.dict("os.environ", {"KIMI_API_KEY": "sk-kimi-key"}),
-            patch("run_agent.OpenAI"),
+        mock_client = _mock_resolve(
+            api_key="sk-kimi-key",
+            base_url="https://api.moonshot.ai/v1",
+        )
+        with patch(
+            "agent.auxiliary_client.resolve_provider_client",
+            return_value=(mock_client, "kimi-k2.5"),
         ):
             assert agent._try_activate_fallback() is True
             assert agent.model == "kimi-k2.5"
@@ -120,23 +133,30 @@ class TestTryActivateFallback:
         agent = _make_agent(
             fallback_model={"provider": "minimax", "model": "MiniMax-M2.5"},
         )
-        with (
-            patch.dict("os.environ", {"MINIMAX_API_KEY": "sk-mm-key"}),
-            patch("run_agent.OpenAI") as mock_openai,
+        mock_client = _mock_resolve(
+            api_key="sk-mm-key",
+            base_url="https://api.minimax.io/v1",
+        )
+        with patch(
+            "agent.auxiliary_client.resolve_provider_client",
+            return_value=(mock_client, "MiniMax-M2.5"),
         ):
             assert agent._try_activate_fallback() is True
             assert agent.model == "MiniMax-M2.5"
             assert agent.provider == "minimax"
-            call_kwargs = mock_openai.call_args[1]
-            assert "minimax.io" in call_kwargs["base_url"]
+            assert agent.client is mock_client
 
     def test_only_fires_once(self):
         agent = _make_agent(
             fallback_model={"provider": "openrouter", "model": "anthropic/claude-sonnet-4"},
         )
-        with (
-            patch.dict("os.environ", {"OPENROUTER_API_KEY": "sk-or-key"}),
-            patch("run_agent.OpenAI"),
+        mock_client = _mock_resolve(
+            api_key="sk-or-key",
+            base_url="https://openrouter.ai/api/v1",
+        )
+        with patch(
+            "agent.auxiliary_client.resolve_provider_client",
+            return_value=(mock_client, "anthropic/claude-sonnet-4"),
         ):
             assert agent._try_activate_fallback() is True
             # Second attempt should return False
@@ -147,9 +167,10 @@ class TestTryActivateFallback:
         agent = _make_agent(
             fallback_model={"provider": "minimax", "model": "MiniMax-M2.5"},
         )
-        # Ensure MINIMAX_API_KEY is not in the environment
-        env = {k: v for k, v in os.environ.items() if k != "MINIMAX_API_KEY"}
-        with patch.dict("os.environ", env, clear=True):
+        with patch(
+            "agent.auxiliary_client.resolve_provider_client",
+            return_value=(None, None),
+        ):
             assert agent._try_activate_fallback() is False
             assert agent._fallback_activated is False
 
@@ -163,22 +184,29 @@ class TestTryActivateFallback:
                 "api_key_env": "MY_CUSTOM_KEY",
             },
         )
-        with (
-            patch.dict("os.environ", {"MY_CUSTOM_KEY": "custom-secret"}),
-            patch("run_agent.OpenAI") as mock_openai,
+        mock_client = _mock_resolve(
+            api_key="custom-secret",
+            base_url="http://localhost:8080/v1",
+        )
+        with patch(
+            "agent.auxiliary_client.resolve_provider_client",
+            return_value=(mock_client, "my-model"),
         ):
             assert agent._try_activate_fallback() is True
-            call_kwargs = mock_openai.call_args[1]
-            assert call_kwargs["base_url"] == "http://localhost:8080/v1"
-            assert call_kwargs["api_key"] == "custom-secret"
+            assert agent.client is mock_client
+            assert agent.model == "my-model"
 
     def test_prompt_caching_enabled_for_claude_on_openrouter(self):
         agent = _make_agent(
             fallback_model={"provider": "openrouter", "model": "anthropic/claude-sonnet-4"},
         )
-        with (
-            patch.dict("os.environ", {"OPENROUTER_API_KEY": "sk-or-key"}),
-            patch("run_agent.OpenAI"),
+        mock_client = _mock_resolve(
+            api_key="sk-or-key",
+            base_url="https://openrouter.ai/api/v1",
+        )
+        with patch(
+            "agent.auxiliary_client.resolve_provider_client",
+            return_value=(mock_client, "anthropic/claude-sonnet-4"),
         ):
             agent._try_activate_fallback()
             assert agent._use_prompt_caching is True
@@ -187,9 +215,13 @@ class TestTryActivateFallback:
         agent = _make_agent(
             fallback_model={"provider": "openrouter", "model": "google/gemini-2.5-flash"},
         )
-        with (
-            patch.dict("os.environ", {"OPENROUTER_API_KEY": "sk-or-key"}),
-            patch("run_agent.OpenAI"),
+        mock_client = _mock_resolve(
+            api_key="sk-or-key",
+            base_url="https://openrouter.ai/api/v1",
+        )
+        with patch(
+            "agent.auxiliary_client.resolve_provider_client",
+            return_value=(mock_client, "google/gemini-2.5-flash"),
         ):
             agent._try_activate_fallback()
             assert agent._use_prompt_caching is False
@@ -198,9 +230,13 @@ class TestTryActivateFallback:
         agent = _make_agent(
             fallback_model={"provider": "zai", "model": "glm-5"},
         )
-        with (
-            patch.dict("os.environ", {"ZAI_API_KEY": "sk-zai-key"}),
-            patch("run_agent.OpenAI"),
+        mock_client = _mock_resolve(
+            api_key="sk-zai-key",
+            base_url="https://open.z.ai/api/v1",
+        )
+        with patch(
+            "agent.auxiliary_client.resolve_provider_client",
+            return_value=(mock_client, "glm-5"),
         ):
             agent._try_activate_fallback()
             assert agent._use_prompt_caching is False
@@ -210,35 +246,36 @@ class TestTryActivateFallback:
         agent = _make_agent(
             fallback_model={"provider": "zai", "model": "glm-5"},
         )
-        with (
-            patch.dict("os.environ", {"Z_AI_API_KEY": "sk-alt-key"}),
-            patch("run_agent.OpenAI") as mock_openai,
+        mock_client = _mock_resolve(
+            api_key="sk-alt-key",
+            base_url="https://open.z.ai/api/v1",
+        )
+        with patch(
+            "agent.auxiliary_client.resolve_provider_client",
+            return_value=(mock_client, "glm-5"),
         ):
             assert agent._try_activate_fallback() is True
-            call_kwargs = mock_openai.call_args[1]
-            assert call_kwargs["api_key"] == "sk-alt-key"
+            assert agent.client is mock_client
 
     def test_activates_codex_fallback(self):
         """OpenAI Codex fallback should use OAuth credentials and codex_responses mode."""
         agent = _make_agent(
             fallback_model={"provider": "openai-codex", "model": "gpt-5.3-codex"},
         )
-        mock_creds = {
-            "api_key": "codex-oauth-token",
-            "base_url": "https://chatgpt.com/backend-api/codex",
-        }
-        with (
-            patch("hermes_cli.auth.resolve_codex_runtime_credentials", return_value=mock_creds),
-            patch("run_agent.OpenAI") as mock_openai,
+        mock_client = _mock_resolve(
+            api_key="codex-oauth-token",
+            base_url="https://chatgpt.com/backend-api/codex",
+        )
+        with patch(
+            "agent.auxiliary_client.resolve_provider_client",
+            return_value=(mock_client, "gpt-5.3-codex"),
         ):
             result = agent._try_activate_fallback()
             assert result is True
             assert agent.model == "gpt-5.3-codex"
             assert agent.provider == "openai-codex"
             assert agent.api_mode == "codex_responses"
-            call_kwargs = mock_openai.call_args[1]
-            assert call_kwargs["api_key"] == "codex-oauth-token"
-            assert "chatgpt.com" in call_kwargs["base_url"]
+            assert agent.client is mock_client
 
     def test_codex_fallback_fails_gracefully_without_credentials(self):
         """Codex fallback should return False if no OAuth credentials available."""
@@ -246,8 +283,8 @@ class TestTryActivateFallback:
             fallback_model={"provider": "openai-codex", "model": "gpt-5.3-codex"},
         )
         with patch(
-            "hermes_cli.auth.resolve_codex_runtime_credentials",
-            side_effect=Exception("No Codex credentials"),
+            "agent.auxiliary_client.resolve_provider_client",
+            return_value=(None, None),
         ):
             assert agent._try_activate_fallback() is False
             assert agent._fallback_activated is False
@@ -257,22 +294,20 @@ class TestTryActivateFallback:
         agent = _make_agent(
             fallback_model={"provider": "nous", "model": "nous-hermes-3"},
         )
-        mock_creds = {
-            "api_key": "nous-agent-key-abc",
-            "base_url": "https://inference-api.nousresearch.com/v1",
-        }
-        with (
-            patch("hermes_cli.auth.resolve_nous_runtime_credentials", return_value=mock_creds),
-            patch("run_agent.OpenAI") as mock_openai,
+        mock_client = _mock_resolve(
+            api_key="nous-agent-key-abc",
+            base_url="https://inference-api.nousresearch.com/v1",
+        )
+        with patch(
+            "agent.auxiliary_client.resolve_provider_client",
+            return_value=(mock_client, "nous-hermes-3"),
         ):
             result = agent._try_activate_fallback()
             assert result is True
             assert agent.model == "nous-hermes-3"
             assert agent.provider == "nous"
             assert agent.api_mode == "chat_completions"
-            call_kwargs = mock_openai.call_args[1]
-            assert call_kwargs["api_key"] == "nous-agent-key-abc"
-            assert "nousresearch.com" in call_kwargs["base_url"]
+            assert agent.client is mock_client
 
     def test_nous_fallback_fails_gracefully_without_login(self):
         """Nous fallback should return False if not logged in."""
@@ -280,8 +315,8 @@ class TestTryActivateFallback:
             fallback_model={"provider": "nous", "model": "nous-hermes-3"},
         )
         with patch(
-            "hermes_cli.auth.resolve_nous_runtime_credentials",
-            side_effect=Exception("Not logged in to Nous Portal"),
+            "agent.auxiliary_client.resolve_provider_client",
+            return_value=(None, None),
         ):
             assert agent._try_activate_fallback() is False
             assert agent._fallback_activated is False
@@ -315,7 +350,7 @@ class TestFallbackInit:
 # =============================================================================
 
 class TestProviderCredentials:
-    """Verify that each supported provider resolves its API key correctly."""
+    """Verify that each supported provider resolves via the centralized router."""
 
     @pytest.mark.parametrize("provider,env_var,base_url_fragment", [
         ("openrouter", "OPENROUTER_API_KEY", "openrouter"),
@@ -328,12 +363,15 @@ class TestProviderCredentials:
         agent = _make_agent(
             fallback_model={"provider": provider, "model": "test-model"},
         )
-        with (
-            patch.dict("os.environ", {env_var: "test-key-123"}),
-            patch("run_agent.OpenAI") as mock_openai,
+        mock_client = MagicMock()
+        mock_client.api_key = "test-api-key"
+        mock_client.base_url = f"https://{base_url_fragment}/v1"
+        with patch(
+            "agent.auxiliary_client.resolve_provider_client",
+            return_value=(mock_client, "test-model"),
         ):
             result = agent._try_activate_fallback()
             assert result is True, f"Failed to activate fallback for {provider}"
-            call_kwargs = mock_openai.call_args[1]
-            assert call_kwargs["api_key"] == "test-key-123"
-            assert base_url_fragment in call_kwargs["base_url"].lower()
+            assert agent.client is mock_client
+            assert agent.model == "test-model"
+            assert agent.provider == provider