refactor(agent): extract tool execution boundary (#5569)

* refactor(agent): extract tool execution boundary

* test(agent): use extracted tool execution boundary

tests/agent/test_runner_errors.py

@@ -9,7 +9,9 @@ from unittest.mock import AsyncMock, MagicMock
 import pytest
 
 from agent.runner_helpers import make_run_spec
+from nanobot.agent.hook import AgentHook, AgentHookContext
 from nanobot.agent.tools import ToolResult
+from nanobot.agent.tools.execution import execute_tool_calls
 from nanobot.config.schema import AgentDefaults
 from nanobot.providers.base import LLMProvider, LLMResponse, ToolCallRequest
 
@@ -55,11 +57,7 @@ async def test_runner_returns_tool_exception_to_model_for_recovery():
 
 @pytest.mark.asyncio
 @pytest.mark.parametrize("control_error", [KeyboardInterrupt, SystemExit])
-async def test_runner_propagates_tool_control_flow_exceptions(control_error: type[BaseException]):
-    from nanobot.agent.runner import AgentRunner
-
-    provider = MagicMock(spec=LLMProvider)
-
+async def test_tool_execution_propagates_control_flow_exceptions(control_error: type[BaseException]):
     async def execute(_name, _args):
         raise control_error("stop")
 
@@ -67,22 +65,15 @@ async def test_runner_propagates_tool_control_flow_exceptions(control_error: typ
         get_definitions=lambda: [],
         execute=execute,
     )
-    runner = AgentRunner()
-    spec = make_run_spec(
-        provider,
-        initial_messages=[],
-        tools=tools,
-        model="test-model",
-        max_iterations=1,
-        max_tool_result_chars=_MAX_TOOL_RESULT_CHARS,
-    )
-
     with pytest.raises(control_error):
-        await runner._run_tool(
-            spec,
-            ToolCallRequest(id="call_1", name="list_dir", arguments={}),
+        await execute_tool_calls(
+            tools,
+            [ToolCallRequest(id="call_1", name="list_dir", arguments={})],
+            concurrent=False,
             external_lookup_counts={},
             workspace_violation_counts={},
+            hook=AgentHook(),
+            context=AgentHookContext(iteration=0, messages=[]),
         )