Fix: align MCP tool call timeout and handle empty content (#13899)

### What problem does this PR solve?
Resolves #12105
This PR fixes two MCP tool call issues in
`common/mcp_tool_call_conn.py`.
First, the timeout passed to `tool_call(..., timeout=...)` was only
applied to the outer `future.result(...)` wait, but was not forwarded to
the internal MCP request. As a result, callers could pass a longer
timeout while the actual MCP request still failed after the default
internal timeout.
Second, the MCP tool call result handling assumed `result.content[0]`
always existed. If an MCP server returned an empty content list, this
could raise an exception unexpectedly.
This PR fixes both issues by:
- forwarding the external `timeout` value to the internal MCP request
timeout
- returning a clear message when the MCP server returns empty content
instead of indexing into an empty list

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)
- [ ] New Feature (non-breaking change which adds functionality)
- [ ] Documentation Update                                             
- [ ] Refactoring                               
- [ ] Performance Improvement
- [ ] Other (please describe)

common/mcp_tool_call_conn.py

@@ -182,6 +182,8 @@ class MCPToolCallSession(ToolCallSession):
             return f"MCP server error: {result.content}"
 
         # For now, we only support text content
+        if not result.content:
+            return "MCP server returned empty content."
         if isinstance(result.content[0], TextContent):
             return result.content[0].text
         else:
@@ -214,7 +216,10 @@ class MCPToolCallSession(ToolCallSession):
         if self._close:
             return "Error: Session is closed"
 
-        future = asyncio.run_coroutine_threadsafe(self._call_mcp_tool(name, arguments), self._event_loop)
+        future = asyncio.run_coroutine_threadsafe(
+            self._call_mcp_tool(name, arguments, request_timeout=timeout),
+            self._event_loop,
+        )
         try:
             return future.result(timeout=timeout)
         except FuturesTimeoutError: