fix(agent): a plugin claiming a host never replaces core's reasoning gate there

R4 W6. _supports_reasoning_extra_body asked the host-claiming profile
(profile_for_host) before the LM Studio / Ollama Cloud / OpenRouter gates, and
_build_chat_completions_kwargs swapped the generic reasoning body for the
profile's payload on any claimed host. A plugin listing openrouter.ai or
ollama.com in hostnames for catalog/aux routing (without overriding
reasoning_payload) silently turned reasoning off on those routes.

_reasoning_endpoint_profile() is the one lookup for both: it returns the
claiming profile except on endpoints core gates itself (Nous Portal, Vercel AI
Gateway, Ollama Cloud, OpenRouter, the lmstudio provider). Documented on
ProviderProfile.hostnames. No in-tree profile claims those hosts; Copilot hosts
are unaffected.

agent/chat_completion_helpers.py

@@ -1442,8 +1442,7 @@ def _build_chat_completions_kwargs(agent, api_messages, tools_for_api, reasoning
     _is_or = agent._is_openrouter_url()
     _host = agent._base_url_lower
     _is_lmstudio = (agent.provider or "").strip().lower() == "lmstudio"
-    from providers import profile_for_host
-    _profile_endpoint = profile_for_host(str(agent.base_url or "")) is not None
+    _profile_endpoint = agent._reasoning_endpoint_profile() is not None
 
     # _fixed_temperature_for_model may return the OMIT_TEMPERATURE sentinel
     # (temperature omitted entirely), a numeric override, or None.

agent/reasoning_params.py

@@ -17,6 +17,9 @@ _OPENROUTER_REASONING_PREFIXES = (
     "qwen/qwen3", "tencent/hy", "xiaomi/",
 )
 
+# Hosts whose reasoning gate core owns: a plugin claiming one in ``hostnames`` never replaces it.
+_CORE_REASONING_GATED_HOSTS = ("nousresearch.com", "ai-gateway.vercel.sh", "ollama.com")
+
 # Probe results cache per (model, base_url). Definitive values cache permanently; an
 # "unknown" value (empty list / None) caches 60s so a transient failure neither sticks
 # for the session nor round-trips every turn.
@@ -92,9 +95,7 @@ class ReasoningParamsMixin:
         url = self._base_url_lower
         if base_url_host_matches(url, "nousresearch.com") or base_url_host_matches(url, "ai-gateway.vercel.sh"):
             return True
-        from providers import profile_for_host
-
-        if (profile := profile_for_host(str(getattr(self, "base_url", None) or ""))) is not None:
+        if (profile := self._reasoning_endpoint_profile()) is not None:
             # A claimed endpoint gates on its own catalog: reasoning goes out iff it declares a payload.
             from agent.provider_route_hooks import ask_profile
             return ask_profile(profile, "reasoning_payload", None, self.model, None,
@@ -137,13 +138,23 @@ class ReasoningParamsMixin:
             return False
         return bool(_cached_probe(self, "_ollama_thinking_cache", ollama_model_supports_thinking, None, lambda v: v is not None))
 
-    def _endpoint_reasoning_payload(self) -> dict | None:
-        """``reasoning_payload`` of the profile claiming this endpoint for the agent's model and
-        ``reasoning_config`` (``providers.profile_for_host``), or None when no profile claims it."""
+    def _reasoning_endpoint_profile(self):
+        """The profile claiming this endpoint (``providers.profile_for_host``) that gates its reasoning, or None.
+        Endpoints core gates itself (Nous Portal, Vercel AI Gateway, LM Studio, Ollama Cloud, OpenRouter) keep
+        core's gate even when a plugin claims their host for metadata or auxiliary routing."""
+        url = self._base_url_lower
+        if ((self.provider or "").strip().lower() == "lmstudio" or self._is_openrouter_url()
+                or any(base_url_host_matches(url, host) for host in _CORE_REASONING_GATED_HOSTS)):
+            return None
         from providers import profile_for_host
 
+        return profile_for_host(str(getattr(self, "base_url", None) or ""))
+
+    def _endpoint_reasoning_payload(self) -> dict | None:
+        """``reasoning_payload`` of the profile gating this endpoint's reasoning for the agent's model and
+        ``reasoning_config`` (``_reasoning_endpoint_profile``), or None when no profile does."""
         base_url = getattr(self, "base_url", None)
-        profile = profile_for_host(str(base_url or ""))
+        profile = self._reasoning_endpoint_profile()
         if profile is None:
             return None
         from agent.provider_route_hooks import ask_profile

providers/base.py

@@ -596,6 +596,8 @@ class ProviderProfile:
     # ── Lane L4: catalog / metadata seams ─────────────────────
     # Hosts (exact or any subdomain) that serve THIS provider's API, so a ``custom`` endpoint or an
     # auto-routed aux client at one of them is recognised as this provider (``providers.profile_for_host``).
+    # It also makes ``reasoning_payload`` the reasoning gate there, except on hosts core gates itself
+    # (OpenRouter, Ollama Cloud, Nous Portal, Vercel AI Gateway, the ``lmstudio`` provider).
     hostnames: tuple = ()
     # Hosts that identify this provider's catalog for model metadata (context length, models.dev) but
     # take other credentials; matched only by ``profile_for_host(url, metadata=True)``.

tests/agent/test_reasoning_gate_claimed_hosts.py

@@ -0,0 +1,47 @@
+"""A plugin claiming a host in ``hostnames`` (catalog / aux routing) never replaces the reasoning gate core
+owns for that host (OpenRouter, Ollama Cloud): only hosts no core gate covers follow ``reasoning_payload``."""
+
+from unittest.mock import MagicMock, patch
+
+import pytest
+
+
+@pytest.fixture
+def claiming_profile(request):
+    import providers
+    from providers.base import ProviderProfile
+
+    providers.list_providers()  # discovery first, so the fake survives it
+    providers.register_provider(ProviderProfile(name="hostclaimer", hostnames=("openrouter.ai", "ollama.com")))
+
+    def _cleanup():
+        providers._REGISTRY.pop("hostclaimer", None)
+        providers._SOURCES.pop("hostclaimer", None)
+        providers._PROVIDER_LIST_CACHE = None
+
+    request.addfinalizer(_cleanup)
+
+
+def _agent(provider, base_url, model):
+    from run_agent import AIAgent
+
+    with patch("agent.process_bootstrap.OpenAI") as mock_openai:
+        mock_openai.return_value = MagicMock()
+        return AIAgent(api_key="k", base_url=base_url, provider=provider, api_mode="chat_completions", model=model,
+                       quiet_mode=True, skip_context_files=True, skip_memory=True, enabled_toolsets=[],
+                       reasoning_config={"enabled": True, "effort": "high"})
+
+
+def test_openrouter_keeps_its_reasoning_gate_and_body_when_a_plugin_claims_the_host(claiming_profile):
+    agent = _agent("openrouter", "https://openrouter.ai/api/v1", "anthropic/claude-sonnet-4.5")
+    with patch("hermes_cli.models_reasoning_caps.openrouter_model_reasoning_capabilities",
+               return_value={"supports_reasoning": True}):
+        assert agent._supports_reasoning_extra_body() is True
+        extra_body = agent._build_api_kwargs([{"role": "user", "content": "x"}]).get("extra_body") or {}
+    assert extra_body.get("reasoning") == {"enabled": True, "effort": "high"}
+
+
+def test_ollama_cloud_keeps_its_capability_gate_when_a_plugin_claims_the_host(claiming_profile):
+    agent = _agent("custom", "https://ollama.com/v1", "gpt-oss:120b")
+    with patch.object(type(agent), "_ollama_supports_thinking_cached", return_value=True):
+        assert agent._supports_reasoning_extra_body() is True