Restore tool cards on thread deserialization (#30053)

Release Notes:

- N/A

---------

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

crates/assistant_tools/src/web_search_tool.rs

@@ -72,7 +72,9 @@ impl Tool for WebSearchTool {
             let search_task = search_task.clone();
             async move {
                 let response = search_task.await.map_err(|err| anyhow!(err))?;
-                serde_json::to_string(&response).context("Failed to serialize search results")
+                serde_json::to_string(&response)
+                    .context("Failed to serialize search results")
+                    .map(Into::into)
             }
         });