fix(subagent): pass reasoning_content and thinking_blocks in subagent messages

Fix issue #1834: Spawn/subagent tool fails with Deepseek Reasoner
due to missing reasoning_content field when using thinking mode.

The subagent was not including reasoning_content and thinking_blocks
in assistant messages with tool calls, causing the Deepseek API to
reject subsequent requests.

- Add reasoning_content to assistant message when subagent makes tool calls
- Add thinking_blocks to assistant message for Anthropic extended thinking
- Add tests to verify both fields are properly passed

Fixes #1834

tests/test_subagent_reasoning.py

@@ -0,0 +1,144 @@
+"""Tests for subagent reasoning_content and thinking_blocks handling."""
+
+from __future__ import annotations
+
+import asyncio
+from pathlib import Path
+from unittest.mock import AsyncMock, MagicMock, patch
+
+import pytest
+
+
+class TestSubagentReasoningContent:
+    """Test that subagent properly handles reasoning_content and thinking_blocks."""
+
+    @pytest.mark.asyncio
+    async def test_subagent_message_includes_reasoning_content(self):
+        """Verify reasoning_content is included in assistant messages with tool calls.
+
+        This is the fix for issue #1834: Spawn/subagent tool fails with
+        Deepseek Reasoner due to missing reasoning_content field.
+        """
+        from nanobot.agent.subagent import SubagentManager
+        from nanobot.bus.queue import MessageBus
+        from nanobot.providers.base import LLMResponse, ToolCallRequest
+
+        bus = MessageBus()
+        provider = MagicMock()
+        provider.get_default_model.return_value = "deepseek-reasoner"
+
+        # Create a real Path object for workspace
+        workspace = Path("/tmp/test_workspace")
+        workspace.mkdir(parents=True, exist_ok=True)
+
+        # Capture messages that are sent to the provider
+        captured_messages = []
+
+        async def mock_chat(*args, **kwargs):
+            captured_messages.append(kwargs.get("messages", []))
+            # Return response with tool calls and reasoning_content
+            tool_call = ToolCallRequest(
+                id="test-1",
+                name="read_file",
+                arguments={"path": "/test.txt"},
+            )
+            return LLMResponse(
+                content="",
+                tool_calls=[tool_call],
+                reasoning_content="I need to read this file first",
+            )
+
+        provider.chat_with_retry = AsyncMock(side_effect=mock_chat)
+
+        mgr = SubagentManager(provider=provider, workspace=workspace, bus=bus)
+
+        # Mock the tools registry
+        with patch("nanobot.agent.subagent.ToolRegistry") as MockToolRegistry:
+            mock_registry = MagicMock()
+            mock_registry.get_definitions.return_value = []
+            mock_registry.execute = AsyncMock(return_value="file content")
+            MockToolRegistry.return_value = mock_registry
+
+            result = await mgr.spawn(
+                task="Read a file",
+                label="test",
+                origin_channel="cli",
+                origin_chat_id="direct",
+                session_key="cli:direct",
+            )
+
+            # Wait for the task to complete
+            await asyncio.sleep(0.5)
+
+        # Check the captured messages
+        assert len(captured_messages) >= 1
+        # Find the assistant message with tool_calls
+        found = False
+        for msg_list in captured_messages:
+            for msg in msg_list:
+                if msg.get("role") == "assistant" and msg.get("tool_calls"):
+                    assert "reasoning_content" in msg, "reasoning_content should be in assistant message with tool_calls"
+                    assert msg["reasoning_content"] == "I need to read this file first"
+                    found = True
+        assert found, "Should have found an assistant message with tool_calls"
+
+    @pytest.mark.asyncio
+    async def test_subagent_message_includes_thinking_blocks(self):
+        """Verify thinking_blocks is included in assistant messages with tool calls."""
+        from nanobot.agent.subagent import SubagentManager
+        from nanobot.bus.queue import MessageBus
+        from nanobot.providers.base import LLMResponse, ToolCallRequest
+
+        bus = MessageBus()
+        provider = MagicMock()
+        provider.get_default_model.return_value = "claude-sonnet"
+
+        workspace = Path("/tmp/test_workspace2")
+        workspace.mkdir(parents=True, exist_ok=True)
+
+        captured_messages = []
+
+        async def mock_chat(*args, **kwargs):
+            captured_messages.append(kwargs.get("messages", []))
+            tool_call = ToolCallRequest(
+                id="test-2",
+                name="read_file",
+                arguments={"path": "/test.txt"},
+            )
+            return LLMResponse(
+                content="",
+                tool_calls=[tool_call],
+                thinking_blocks=[
+                    {"signature": "sig1", "thought": "thinking step 1"},
+                    {"signature": "sig2", "thought": "thinking step 2"},
+                ],
+            )
+
+        provider.chat_with_retry = AsyncMock(side_effect=mock_chat)
+
+        mgr = SubagentManager(provider=provider, workspace=workspace, bus=bus)
+
+        with patch("nanobot.agent.subagent.ToolRegistry") as MockToolRegistry:
+            mock_registry = MagicMock()
+            mock_registry.get_definitions.return_value = []
+            mock_registry.execute = AsyncMock(return_value="file content")
+            MockToolRegistry.return_value = mock_registry
+
+            result = await mgr.spawn(
+                task="Read a file",
+                label="test",
+                origin_channel="cli",
+                origin_chat_id="direct",
+            )
+
+            await asyncio.sleep(0.5)
+
+        # Check the captured messages
+        found = False
+        for msg_list in captured_messages:
+            for msg in msg_list:
+                if msg.get("role") == "assistant" and msg.get("tool_calls"):
+                    assert "thinking_blocks" in msg, "thinking_blocks should be in assistant message with tool_calls"
+                    assert len(msg["thinking_blocks"]) == 2
+                    found = True
+        assert found, "Should have found an assistant message with tool_calls"