Restore tool cards on thread deserialization (#30053)

Release Notes:

- N/A

---------

Co-authored-by: Julia Ryan <juliaryan3.14@gmail.com>

crates/assistant_tools/src/open_tool.rs

@@ -70,7 +70,7 @@ impl Tool for OpenTool {
             }
             .context("Failed to open URL or file path")?;
 
-            Ok(format!("Successfully opened {}", input.path_or_url))
+            Ok(format!("Successfully opened {}", input.path_or_url).into())
         })
         .into()
     }