fix: make subagent fail_on_tool_error configurable (#4198)

Add fail_on_tool_error to AgentDefaults and wire it through
AgentLoop -> SubagentManager -> AgentRunSpec.

Previously hardcoded to True in SubagentManager._run_subagent.
Now configurable via config.json with default True for backward
compatibility. When set to False, subagents can retry on minor
tool errors instead of immediately failing.

Changes:
- nanobot/config/schema.py: add fail_on_tool_error field (default True)
- nanobot/agent/subagent.py: accept and forward fail_on_tool_error
- nanobot/agent/loop.py: pass config through to SubagentManager
- tests/agent/test_subagent.py: add regression test

Signed-off-by: axelray-dev <110029405+axelray-dev@users.noreply.github.com>

tests/agent/test_subagent.py

@@ -1,11 +1,12 @@
 """Tests for SubagentManager."""
 
 from pathlib import Path
-from unittest.mock import MagicMock
+from unittest.mock import AsyncMock, MagicMock
 
 import pytest
 
-from nanobot.agent.subagent import SubagentManager
+from nanobot.agent.runner import AgentRunResult
+from nanobot.agent.subagent import SubagentManager, SubagentStatus
 from nanobot.agent.tools.filesystem import FileToolsConfig
 from nanobot.bus.queue import MessageBus
 from nanobot.config.schema import ToolsConfig
@@ -79,3 +80,33 @@ def test_subagent_respects_file_tool_toggle(tmp_path):
         "write_file",
     }
     assert file_tools.isdisjoint(tools.tool_names)
+
+
+@pytest.mark.asyncio
+async def test_subagent_forwards_fail_on_tool_error_to_runner(tmp_path):
+    provider = MagicMock(spec=LLMProvider)
+    provider.get_default_model.return_value = "test"
+    sm = SubagentManager(
+        provider=provider,
+        workspace=tmp_path,
+        bus=MessageBus(),
+        model="test",
+        max_tool_result_chars=16_000,
+        fail_on_tool_error=False,
+    )
+    sm.runner.run = AsyncMock(
+        return_value=AgentRunResult(final_content="ok", messages=[], stop_reason="completed")
+    )
+    sm._announce_result = AsyncMock()
+
+    status = SubagentStatus(
+        task_id="t1",
+        label="label",
+        task_description="task",
+        started_at=0.0,
+    )
+
+    await sm._run_subagent("t1", "task", "label", {"channel": "cli", "chat_id": "direct"}, status)
+
+    spec = sm.runner.run.call_args.args[0]
+    assert spec.fail_on_tool_error is False