diff --git a/tests/agents/test_config_defaults.py b/tests/agents/test_config_defaults.py
new file mode 100644
index 00000000..95493bdd
--- /dev/null
+++ b/tests/agents/test_config_defaults.py
@@ -0,0 +1,167 @@
+"""Tests for agent constructor config-based default resolution."""
+
+from __future__ import annotations
+
+from unittest.mock import MagicMock, patch
+
+from openjarvis.agents._stubs import AgentResult, BaseAgent, ToolUsingAgent
+
+
+class _TestAgent(BaseAgent):
+    agent_id = "test_cfg"
+
+    def run(self, input, context=None, **kwargs):
+        return AgentResult(content="ok", turns=1)
+
+
+class _TestToolAgent(ToolUsingAgent):
+    agent_id = "test_cfg_tool"
+
+    def run(self, input, context=None, **kwargs):
+        return AgentResult(content="ok", turns=1)
+
+
+class _TestToolAgentWithDefaults(ToolUsingAgent):
+    """Agent with class-level defaults (like MonitorOperativeAgent)."""
+
+    agent_id = "test_cfg_tool_defaults"
+    _default_temperature = 0.3
+    _default_max_tokens = 4096
+    _default_max_turns = 25
+
+    def run(self, input, context=None, **kwargs):
+        return AgentResult(content="ok", turns=1)
+
+
+class TestBaseAgentConfigResolution:
+    """BaseAgent resolves None params from config.intelligence."""
+
+    def test_none_temperature_reads_config(self):
+        """When temperature is not passed, it should come from config."""
+        engine = MagicMock()
+        with patch("openjarvis.agents._stubs.load_config") as mock_cfg:
+            mock_cfg.return_value.intelligence.temperature = 0.2
+            mock_cfg.return_value.intelligence.max_tokens = 512
+            agent = _TestAgent(engine, "m")
+        assert agent._temperature == 0.2
+
+    def test_none_max_tokens_reads_config(self):
+        """When max_tokens is not passed, it should come from config."""
+        engine = MagicMock()
+        with patch("openjarvis.agents._stubs.load_config") as mock_cfg:
+            mock_cfg.return_value.intelligence.temperature = 0.7
+            mock_cfg.return_value.intelligence.max_tokens = 512
+            agent = _TestAgent(engine, "m")
+        assert agent._max_tokens == 512
+
+    def test_explicit_temperature_overrides_config(self):
+        """Caller-provided temperature takes precedence over config."""
+        engine = MagicMock()
+        agent = _TestAgent(engine, "m", temperature=0.9)
+        assert agent._temperature == 0.9
+
+    def test_explicit_max_tokens_overrides_config(self):
+        """Caller-provided max_tokens takes precedence over config."""
+        engine = MagicMock()
+        agent = _TestAgent(engine, "m", max_tokens=2048)
+        assert agent._max_tokens == 2048
+
+    def test_partial_override_temperature_only(self):
+        """Providing only temperature still reads max_tokens from config."""
+        engine = MagicMock()
+        with patch("openjarvis.agents._stubs.load_config") as mock_cfg:
+            mock_cfg.return_value.intelligence.temperature = 0.2
+            mock_cfg.return_value.intelligence.max_tokens = 512
+            agent = _TestAgent(engine, "m", temperature=0.9)
+        assert agent._temperature == 0.9
+        assert agent._max_tokens == 512
+
+    def test_config_load_failure_uses_hardcoded_fallback(self):
+        """When config loading fails, fall back to class defaults then 0.7/1024."""
+        engine = MagicMock()
+        with patch(
+            "openjarvis.agents._stubs.load_config",
+            side_effect=Exception("boom"),
+        ):
+            agent = _TestAgent(engine, "m")
+        assert agent._temperature == 0.7
+        assert agent._max_tokens == 1024
+
+
+class TestToolUsingAgentConfigResolution:
+    """ToolUsingAgent resolves None max_turns from config.agent."""
+
+    def test_none_max_turns_reads_config(self):
+        """When max_turns is not passed, it should come from config."""
+        engine = MagicMock()
+        with patch("openjarvis.agents._stubs.load_config") as mock_cfg:
+            mock_cfg.return_value.intelligence.temperature = 0.7
+            mock_cfg.return_value.intelligence.max_tokens = 1024
+            mock_cfg.return_value.agent.max_turns = 15
+            agent = _TestToolAgent(engine, "m")
+        assert agent._max_turns == 15
+
+    def test_explicit_max_turns_overrides_config(self):
+        """Caller-provided max_turns takes precedence over config."""
+        engine = MagicMock()
+        agent = _TestToolAgent(engine, "m", max_turns=5)
+        assert agent._max_turns == 5
+
+    def test_temperature_and_max_tokens_forwarded_to_base(self):
+        """ToolUsingAgent also resolves temperature/max_tokens from config."""
+        engine = MagicMock()
+        with patch("openjarvis.agents._stubs.load_config") as mock_cfg:
+            mock_cfg.return_value.intelligence.temperature = 0.1
+            mock_cfg.return_value.intelligence.max_tokens = 256
+            mock_cfg.return_value.agent.max_turns = 10
+            agent = _TestToolAgent(engine, "m")
+        assert agent._temperature == 0.1
+        assert agent._max_tokens == 256
+
+    def test_config_load_failure_max_turns_fallback(self):
+        """When config loading fails, max_turns falls back to class default then 10."""
+        engine = MagicMock()
+        with patch(
+            "openjarvis.agents._stubs.load_config",
+            side_effect=Exception("boom"),
+        ):
+            agent = _TestToolAgent(engine, "m")
+        assert agent._max_turns == 10
+
+
+class TestClassLevelDefaults:
+    """Agents with class-level _default_* attributes use them as fallback."""
+
+    def test_class_default_used_when_config_fails(self):
+        """Agent class defaults are used when config is unavailable."""
+        engine = MagicMock()
+        with patch(
+            "openjarvis.agents._stubs.load_config",
+            side_effect=Exception("boom"),
+        ):
+            agent = _TestToolAgentWithDefaults(engine, "m")
+        assert agent._temperature == 0.3
+        assert agent._max_tokens == 4096
+        assert agent._max_turns == 25
+
+    def test_config_overrides_class_default(self):
+        """User config takes precedence over class-level defaults."""
+        engine = MagicMock()
+        with patch("openjarvis.agents._stubs.load_config") as mock_cfg:
+            mock_cfg.return_value.intelligence.temperature = 0.5
+            mock_cfg.return_value.intelligence.max_tokens = 2048
+            mock_cfg.return_value.agent.max_turns = 12
+            agent = _TestToolAgentWithDefaults(engine, "m")
+        assert agent._temperature == 0.5
+        assert agent._max_tokens == 2048
+        assert agent._max_turns == 12
+
+    def test_explicit_overrides_everything(self):
+        """Caller-provided values override both config and class defaults."""
+        engine = MagicMock()
+        agent = _TestToolAgentWithDefaults(
+            engine, "m", temperature=0.9, max_tokens=100, max_turns=2,
+        )
+        assert agent._temperature == 0.9
+        assert agent._max_tokens == 100
+        assert agent._max_turns == 2