Add execution field to base Tool class

The base Tool class now has an optional `execution` field for storing
task execution metadata (SEP-1686). This lets gateways/proxies preserve
execution info when forwarding tools from backends - previously this
metadata was lost because Tool had no way to store it.

FunctionTool continues to derive execution from task_config as before.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/fastmcp/tools/tool.py

@@ -133,6 +133,10 @@ class Tool(FastMCPComponent):
         ToolAnnotations | None,
         Field(description="Additional annotations about the tool"),
     ] = None
+    execution: Annotated[
+        ToolExecution | None,
+        Field(description="Task execution configuration (SEP-1686)"),
+    ] = None
     serializer: Annotated[
         ToolResultSerializerType | None,
         Field(description="Optional custom serializer for tool results"),
@@ -182,7 +186,7 @@ class Tool(FastMCPComponent):
             outputSchema=overrides.get("outputSchema", self.output_schema),
             icons=overrides.get("icons", self.icons),
             annotations=overrides.get("annotations", self.annotations),
-            execution=overrides.get("execution"),
+            execution=overrides.get("execution", self.execution),
             _meta=overrides.get(
                 "_meta", self.get_meta(include_fastmcp_meta=include_fastmcp_meta)
             ),

tests/tools/test_tool.py

@@ -12,6 +12,7 @@ from mcp.types import (
     ResourceLink,
     TextContent,
     TextResourceContents,
+    ToolExecution,
 )
 from pydantic import AnyUrl, BaseModel, Field, TypeAdapter
 from typing_extensions import TypedDict
@@ -1813,3 +1814,84 @@ class TestToolNameValidation:
         assert tool.parameters is not None
         assert "a" in tool.parameters["properties"]
         assert "b" in tool.parameters["properties"]
+
+
+class TestToolExecutionField:
+    """Tests for the execution field on the base Tool class."""
+
+    def test_tool_with_execution_field(self):
+        """Test that Tool can store and return execution metadata."""
+        tool = Tool(
+            name="my_tool",
+            description="A tool with execution",
+            parameters={"type": "object", "properties": {}},
+            execution=ToolExecution(taskSupport="optional"),
+        )
+
+        mcp_tool = tool.to_mcp_tool()
+        assert mcp_tool.execution is not None
+        assert mcp_tool.execution.taskSupport == "optional"
+
+    def test_tool_without_execution_field(self):
+        """Test that Tool without execution returns None."""
+        tool = Tool(
+            name="my_tool",
+            description="A tool without execution",
+            parameters={"type": "object", "properties": {}},
+        )
+
+        mcp_tool = tool.to_mcp_tool()
+        assert mcp_tool.execution is None
+
+    def test_execution_override_takes_precedence(self):
+        """Test that explicit override takes precedence over field value."""
+        tool = Tool(
+            name="my_tool",
+            description="A tool",
+            parameters={"type": "object", "properties": {}},
+            execution=ToolExecution(taskSupport="optional"),
+        )
+
+        override_execution = ToolExecution(taskSupport="required")
+        mcp_tool = tool.to_mcp_tool(execution=override_execution)
+        assert mcp_tool.execution is not None
+        assert mcp_tool.execution.taskSupport == "required"
+
+    async def test_function_tool_task_config_still_works(self):
+        """FunctionTool should still derive execution from task_config."""
+
+        async def my_fn() -> str:
+            return "hello"
+
+        tool = Tool.from_function(my_fn, task=True)
+        mcp_tool = tool.to_mcp_tool()
+
+        # FunctionTool sets execution from task_config
+        assert mcp_tool.execution is not None
+        assert mcp_tool.execution.taskSupport == "optional"
+
+    def test_tool_execution_required_mode(self):
+        """Test that Tool can store required execution mode."""
+        tool = Tool(
+            name="my_tool",
+            description="A tool with required execution",
+            parameters={"type": "object", "properties": {}},
+            execution=ToolExecution(taskSupport="required"),
+        )
+
+        mcp_tool = tool.to_mcp_tool()
+        assert mcp_tool.execution is not None
+        assert mcp_tool.execution.taskSupport == "required"
+
+    def test_tool_execution_forbidden_mode(self):
+        """Test that Tool can store forbidden execution mode."""
+        tool = Tool(
+            name="my_tool",
+            description="A tool with forbidden execution",
+            parameters={"type": "object", "properties": {}},
+            execution=ToolExecution(taskSupport="forbidden"),
+        )
+
+        mcp_tool = tool.to_mcp_tool()
+        assert mcp_tool.execution is not None
+        assert mcp_tool.execution.taskSupport == "forbidden"