fix(server): preserve mounted tool task metadata (#3632)

* fix(server): preserve mounted tool task metadata

* fix(server): move task execution metadata to base tool

* cleanup: remove stale import, tighten execution metadata guard

---------

Co-authored-by: Jeremiah Lowin <153965+jlowin@users.noreply.github.com>

src/fastmcp/server/providers/fastmcp_provider.py

@@ -104,6 +104,7 @@ class FastMCPProviderTool(Tool):
             tags=tool.tags,
             annotations=tool.annotations,
             task_config=tool.task_config,
+            execution=tool.execution,
             meta=tool.get_meta(),
             title=tool.title,
             icons=tool.icons,

src/fastmcp/tools/base.py

@@ -190,7 +190,7 @@ class Tool(FastMCPComponent):
         elif self.annotations and self.annotations.title:
             title = self.annotations.title
 
-        return MCPTool(
+        mcp_tool = MCPTool(
             name=overrides.get("name", self.name),
             title=overrides.get("title", title),
             description=overrides.get("description", self.description),
@@ -204,6 +204,15 @@ class Tool(FastMCPComponent):
             ),  # ty:ignore[unknown-argument]
         )
 
+        if (
+            self.task_config.supports_tasks()
+            and "execution" not in overrides
+            and not self.execution
+        ):
+            mcp_tool.execution = ToolExecution(taskSupport=self.task_config.mode)
+
+        return mcp_tool
+
     @classmethod
     def from_function(
         cls,

src/fastmcp/tools/function_tool.py

@@ -18,9 +18,8 @@ from typing import (
 )
 
 import anyio
-import mcp.types
 from mcp.shared.exceptions import McpError
-from mcp.types import ErrorData, Icon, ToolAnnotations, ToolExecution
+from mcp.types import ErrorData, Icon, ToolAnnotations
 from pydantic import Field
 from pydantic.json_schema import SkipJsonSchema
 
@@ -91,24 +90,6 @@ class FunctionTool(Tool):
     fn: SkipJsonSchema[Callable[..., Any]]
     return_type: Annotated[SkipJsonSchema[Any], Field(exclude=True)] = None
 
-    def to_mcp_tool(
-        self,
-        **overrides: Any,
-    ) -> mcp.types.Tool:
-        """Convert the FastMCP tool to an MCP tool.
-
-        Extends the base implementation to add task execution mode if enabled.
-        """
-        # Get base MCP tool from parent
-        mcp_tool = super().to_mcp_tool(**overrides)
-
-        # Add task execution mode per SEP-1686
-        # Only set execution if not overridden and task execution is supported
-        if self.task_config.supports_tasks() and "execution" not in overrides:
-            mcp_tool.execution = ToolExecution(taskSupport=self.task_config.mode)
-
-        return mcp_tool
-
     @classmethod
     def from_function(
         cls,

tests/server/tasks/test_task_mount.py

@@ -473,6 +473,35 @@ class TestMountedTaskList:
             assert child_task.task_id in task_ids
 
 
+class TestMountedTaskMetadata:
+    """Test task metadata exposure for mounted tools."""
+
+    async def test_mounted_tool_list_preserves_task_support_metadata(self):
+        """Mounted tools should preserve execution.taskSupport in tools/list."""
+        child = FastMCP("child")
+
+        @child.tool(task=True)
+        async def foo() -> dict[str, bool]:
+            return {"ok": True}
+
+        parent = FastMCP("parent")
+        parent.mount(child)
+
+        child_tools = await child.list_tools()
+        parent_tools = await parent.list_tools()
+
+        child_tool = next(t for t in child_tools if t.name == "foo")
+        parent_tool = next(t for t in parent_tools if t.name == "foo")
+
+        child_mcp_tool = child_tool.to_mcp_tool(name=child_tool.name)
+        parent_mcp_tool = parent_tool.to_mcp_tool(name=parent_tool.name)
+
+        assert child_mcp_tool.execution is not None
+        assert parent_mcp_tool.execution is not None
+        assert child_mcp_tool.execution.taskSupport == "optional"
+        assert parent_mcp_tool.execution.taskSupport == "optional"
+
+
 class TestMountedTaskConfigModes:
     """Test TaskConfig mode enforcement for mounted tools."""