fix: address review comments - remove duplicate logging and add defensive handler test

- Remove logger.exception from base.py Tool.run() to avoid duplicate
  logging (server.py's defensive handler already logs)
- Remove unused logging import from base.py
- Remove '# pragma: no cover' from server.py defensive exception handler
- Add test_handle_call_tool_defensive_exception_handler to verify
  the defensive handler returns a generic error and does not leak
  internal exception details

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: Varun Sharma

src/mcp/server/mcpserver/server.py

@@ -306,7 +306,7 @@ async def _handle_call_tool(
             raise
         except ToolError as e:
             return CallToolResult(content=[TextContent(type="text", text=str(e))], is_error=True)
-        except Exception:  # pragma: no cover
+        except Exception:
             logger.exception(f"Error calling tool {params.name}")
             return CallToolResult(
                 content=[TextContent(type="text", text=f"An unexpected error occurred calling tool {params.name}")],

src/mcp/server/mcpserver/tools/base.py

@@ -2,7 +2,6 @@
 
 import functools
 import inspect
-import logging
 from collections.abc import Callable
 from functools import cached_property
 from typing import TYPE_CHECKING, Any
@@ -16,8 +15,6 @@
 from mcp.shared.tool_name_validation import validate_and_warn_tool_name
 from mcp.types import Icon, ToolAnnotations
 
-logger = logging.getLogger(__name__)
-
 if TYPE_CHECKING:
     from mcp.server.context import LifespanContextT, RequestT
     from mcp.server.mcpserver.server import Context
@@ -118,7 +115,6 @@ async def run(
         except ToolError:
             raise
         except Exception as e:
-            logger.exception(f"Error executing tool {self.name}")
             raise ToolError(f"An unexpected error occurred executing tool {self.name}") from e
 
 

tests/server/mcpserver/test_server.py

@@ -302,6 +302,26 @@ async def test_tool_error_passthrough(self):
             assert isinstance(content, TextContent)
             assert "Intentional tool error" in content.text
 
+    async def test_handle_call_tool_defensive_exception_handler(self):
+        """Test that _handle_call_tool returns generic error when call_tool raises unexpected Exception."""
+        mcp = MCPServer()
+        mcp.add_tool(tool_fn)
+
+        original_call_tool = mcp.call_tool
+
+        async def patched_call_tool(name: str, arguments: dict[str, Any]) -> Any:
+            raise RuntimeError("internal db connection string leaked")
+
+        async with Client(mcp) as client:
+            mcp.call_tool = patched_call_tool  # type: ignore[assignment]
+            result = await client.call_tool("tool_fn", {"x": 1, "y": 2})
+            mcp.call_tool = original_call_tool  # type: ignore[assignment]
+            assert result.is_error is True
+            content = result.content[0]
+            assert isinstance(content, TextContent)
+            assert "unexpected error" in content.text.lower()
+            assert "internal db connection string leaked" not in content.text
+
     async def test_tool_return_value_conversion(self):
         mcp = MCPServer()
         mcp.add_tool(tool_fn)