refactor(tools): use structured tool error results

tests/agent/test_runner_safety.py

@@ -6,6 +6,8 @@ from unittest.mock import AsyncMock, MagicMock
 
 import pytest
 
+from nanobot.agent.runner import AgentRunner, AgentRunSpec
+from nanobot.agent.tools import ToolResult
 from nanobot.config.schema import AgentDefaults
 from nanobot.providers.base import LLMResponse, ToolCallRequest
 
@@ -20,8 +22,6 @@ async def test_runner_does_not_abort_on_workspace_violation_anymore():
     we now hand the error back to the LLM as a recoverable tool result and
     rely on ``repeated_workspace_violation_error`` to throttle bypass loops.
     """
-    from nanobot.agent.runner import AgentRunSpec, AgentRunner
-
     provider = MagicMock()
     provider.chat_with_retry = AsyncMock(side_effect=[
         LLMResponse(
@@ -64,8 +64,6 @@ async def test_runner_does_not_abort_on_workspace_violation_anymore():
 
 def test_is_ssrf_violation_recognizes_private_url_blocks():
     """SSRF rejections are classified separately from workspace boundaries."""
-    from nanobot.agent.runner import AgentRunner
-
     ssrf_msg = "Error: Command blocked by safety guard (internal/private URL detected)"
     assert AgentRunner._is_ssrf_violation(ssrf_msg) is True
     assert AgentRunner._is_ssrf_violation(
@@ -88,8 +86,6 @@ def test_is_ssrf_violation_recognizes_private_url_blocks():
 @pytest.mark.asyncio
 async def test_runner_returns_non_retryable_hint_on_ssrf_violation():
     """SSRF stays blocked, but the runtime gives the LLM a final chance to recover."""
-    from nanobot.agent.runner import AgentRunSpec, AgentRunner
-
     provider = MagicMock()
     provider.chat_with_retry = AsyncMock(side_effect=[
         LLMResponse(
@@ -107,7 +103,7 @@ async def test_runner_returns_non_retryable_hint_on_ssrf_violation():
     ])
     tools = MagicMock()
     tools.get_definitions.return_value = []
-    tools.execute = AsyncMock(return_value=(
+    tools.execute = AsyncMock(return_value=ToolResult.error(
         "Error: Command blocked by safety guard (internal/private URL detected)"
     ))
 
@@ -141,8 +137,6 @@ async def test_runner_lets_llm_recover_from_shell_guard_path_outside():
     turn (silent hang on Telegram per #3605); now the LLM gets the soft
     error back and can finalize on the next iteration.
     """
-    from nanobot.agent.runner import AgentRunSpec, AgentRunner
-
     provider = MagicMock()
     captured_second_call: list[dict] = []
 
@@ -163,7 +157,9 @@ async def test_runner_lets_llm_recover_from_shell_guard_path_outside():
     tools = MagicMock()
     tools.get_definitions.return_value = []
     tools.execute = AsyncMock(
-        return_value="Error: Command blocked by safety guard (path outside working dir)"
+        return_value=ToolResult.error(
+            "Error: Command blocked by safety guard (path outside working dir)"
+        )
     )
 
     runner = AgentRunner(provider)
@@ -195,8 +191,6 @@ async def test_runner_throttles_repeated_workspace_bypass_attempts():
     the runner replaces the tool result with a hard "stop trying" message
     so the model finally gives up and surfaces the boundary to the user.
     """
-    from nanobot.agent.runner import AgentRunSpec, AgentRunner
-
     bypass_attempts = [
         ToolCallRequest(
             id=f"a{i}", name="exec",
@@ -215,7 +209,9 @@ async def test_runner_throttles_repeated_workspace_bypass_attempts():
     tools = MagicMock()
     tools.get_definitions.return_value = []
     tools.execute = AsyncMock(
-        return_value="Error: Command blocked by safety guard (path outside working dir)"
+        return_value=ToolResult.error(
+            "Error: Command blocked by safety guard (path outside working dir)"
+        )
     )
 
     runner = AgentRunner(provider)