fix(agent): let subagents recover from tool errors

tests/agent/test_task_cancel.py

@@ -450,7 +450,9 @@ class TestSubagentCancellation:
         mgr._announce_result.assert_awaited_once()
 
     @pytest.mark.asyncio
-    async def test_subagent_announces_error_when_tool_execution_fails(self, monkeypatch, tmp_path):
+    async def test_subagent_announces_success_after_recovering_from_tool_failure(
+        self, monkeypatch, tmp_path
+    ):
         from nanobot.agent.subagent import SubagentManager
         from nanobot.bus.queue import MessageBus
         from nanobot.providers.base import LLMResponse, ToolCallRequest
@@ -458,10 +460,21 @@ class TestSubagentCancellation:
         bus = MessageBus()
         provider = MagicMock()
         provider.get_default_model.return_value = "test-model"
-        provider.chat_with_retry = AsyncMock(return_value=LLMResponse(
-            content="thinking",
-            tool_calls=[ToolCallRequest(id="call_1", name="list_dir", arguments={"path": "."})],
-        ))
+        provider.chat_with_retry = AsyncMock(side_effect=[
+            LLMResponse(
+                content="first attempt",
+                tool_calls=[
+                    ToolCallRequest(id="call_1", name="list_dir", arguments={"path": "."})
+                ],
+            ),
+            LLMResponse(
+                content="retrying",
+                tool_calls=[
+                    ToolCallRequest(id="call_2", name="list_dir", arguments={"path": "."})
+                ],
+            ),
+            LLMResponse(content="recovered after tool failure", tool_calls=[]),
+        ])
         mgr = SubagentManager(
             workspace=tmp_path,
             bus=bus,
@@ -492,11 +505,10 @@ class TestSubagentCancellation:
 
         mgr._announce_result.assert_awaited_once()
         args = mgr._announce_result.await_args.args
-        assert "Completed steps:" in args[3]
-        assert "- list_dir: first result" in args[3]
-        assert "Failure:" in args[3]
-        assert "- list_dir: boom" in args[3]
-        assert args[5] == "error"
+        assert args[3] == "recovered after tool failure"
+        assert args[5] == "ok"
+        assert calls["n"] == 2
+        assert provider.chat_with_retry.await_count == 3
 
     @pytest.mark.asyncio
     async def test_cancel_by_session_cancels_running_subagent_tool(self, monkeypatch, tmp_path):