feat(ollama): pass think=false to custom providers when reasoning_effort is none

When a custom/Ollama provider is used and reasoning_effort is set to 'none'
(or enabled: false), inject 'think': false into the request extra_body.

Ollama does not recognise the OpenRouter-style 'reasoning' extra_body field,
so thinking-capable models (Qwen3, etc.) generate <think> blocks regardless
of the reasoning_effort setting. This produces empty-response errors that
corrupt session state.

The fix adds a provider-specific block in _build_api_kwargs() that sets
think=false in extra_body whenever self.provider == 'custom' and reasoning
is explicitly disabled.

Closes #3191

tests/run_agent/test_run_agent.py

@@ -928,6 +928,7 @@ class TestBuildApiKwargs:
         kwargs = agent._build_api_kwargs(messages)
         assert kwargs["max_tokens"] == 4096
 
+
     def test_qwen_portal_formats_messages_and_metadata(self, agent):
         agent.base_url = "https://portal.qwen.ai/v1"
         agent._base_url_lower = agent.base_url.lower()
@@ -983,6 +984,46 @@ class TestBuildApiKwargs:
         messages = [{"role": "system", "content": "sys"}, {"role": "user", "content": "hi"}]
         kwargs = agent._build_api_kwargs(messages)
         assert kwargs["max_tokens"] == 65536
+=======
+    def test_ollama_think_false_on_effort_none(self, agent):
+        """Custom (Ollama) provider with effort=none should inject think=false."""
+        agent.provider = "custom"
+        agent.base_url = "http://localhost:11434/v1"
+        agent._base_url_lower = agent.base_url.lower()
+        agent.reasoning_config = {"effort": "none"}
+        messages = [{"role": "user", "content": "hi"}]
+        kwargs = agent._build_api_kwargs(messages)
+        assert kwargs.get("extra_body", {}).get("think") is False
+
+    def test_ollama_think_false_on_enabled_false(self, agent):
+        """Custom (Ollama) provider with enabled=false should inject think=false."""
+        agent.provider = "custom"
+        agent.base_url = "http://localhost:11434/v1"
+        agent._base_url_lower = agent.base_url.lower()
+        agent.reasoning_config = {"enabled": False}
+        messages = [{"role": "user", "content": "hi"}]
+        kwargs = agent._build_api_kwargs(messages)
+        assert kwargs.get("extra_body", {}).get("think") is False
+
+    def test_ollama_no_think_param_when_reasoning_enabled(self, agent):
+        """Custom provider with reasoning enabled should NOT inject think=false."""
+        agent.provider = "custom"
+        agent.base_url = "http://localhost:11434/v1"
+        agent._base_url_lower = agent.base_url.lower()
+        agent.reasoning_config = {"enabled": True, "effort": "medium"}
+        messages = [{"role": "user", "content": "hi"}]
+        kwargs = agent._build_api_kwargs(messages)
+        assert kwargs.get("extra_body", {}).get("think") is None
+
+    def test_non_custom_provider_unaffected(self, agent):
+        """OpenRouter provider with effort=none should NOT inject think=false."""
+        agent.provider = "openrouter"
+        agent.model = "qwen/qwen3.5-plus-02-15"
+        agent.reasoning_config = {"effort": "none"}
+        messages = [{"role": "user", "content": "hi"}]
+        kwargs = agent._build_api_kwargs(messages)
+        assert kwargs.get("extra_body", {}).get("think") is None
+
 
 
 class TestBuildAssistantMessage: