fix: remove dead code path in _handle_call_tool and correct call_tool return type

The isinstance(result, dict) branch in _handle_call_tool is unreachable
because FuncMetadata.convert_result never returns a raw dict -- it returns
CallToolResult, Sequence[ContentBlock], or a tuple of
(Sequence[ContentBlock], dict[str, Any]).

This change:
- Removes the dead dict branch
- Drops the now-unused import json
- Corrects call_tool's return type annotation to reflect the actual
  return shapes

Closes #2695

Co-authored-by: AI assistant (code review and diff structuring)
Signed-off-by: Wahaj Ahmed <wahaj.ahmed010@gmail.com>

Author: wahajahmed010

src/mcp/server/mcpserver/server.py

@@ -4,7 +4,6 @@
 
 import base64
 import inspect
-import json
 import re
 from collections.abc import AsyncIterator, Awaitable, Callable, Iterable, Sequence
 from contextlib import AbstractAsyncContextManager, asynccontextmanager
@@ -322,14 +321,6 @@ async def _handle_call_tool(
                 content=list(unstructured_content),  # type: ignore[arg-type]
                 structured_content=structured_content,  # type: ignore[arg-type]
             )
-        if isinstance(result, dict):  # pragma: no cover
-            # TODO: this code path is unreachable — convert_result never returns a raw dict.
-            # The call_tool return type (Sequence[ContentBlock] | dict[str, Any]) is wrong
-            # and needs to be cleaned up.
-            return CallToolResult(
-                content=[TextContent(type="text", text=json.dumps(result, indent=2))],
-                structured_content=result,
-            )
         return CallToolResult(content=list(result))
 
     async def _handle_list_resources(
@@ -399,7 +390,7 @@ async def list_tools(self) -> list[MCPTool]:
 
     async def call_tool(
         self, name: str, arguments: dict[str, Any], context: Context[LifespanResultT, Any] | None = None
-    ) -> Sequence[ContentBlock] | dict[str, Any]:
+    ) -> CallToolResult | Sequence[ContentBlock] | tuple[Sequence[ContentBlock], dict[str, Any]]:
         """Call a tool by name with arguments."""
         if context is None:
             context = Context(mcp_server=self)