feat: tool call results are not sent back to model, giving json results back to user instead of human readable text

[carlos-verdes]

• [ X] I have looked for existing issues (including closed) about this

Bug Report

Tool results should be passed back to the model to generate a human readable answer.
Currently the tool result is sent back to the user.

Reproduction

You can simply run any example agent with a tool which response is a structured model.

If you run an agent with the below SearchTool you will get a conversation like this:

Prompt: Can you please let me know title and url of rig platform?
Response: {"title":"Rig Documentation","url":"https://docs.rig.ai"}

SearchTool implementation:

#[derive(Deserialize, Serialize)]
struct SearchArgs {
    pub query_string: String,
}

#[derive(Deserialize, Serialize)]
struct SearchResult {
    pub title: String,
    pub url: String,
}

#[derive(Debug, thiserror::Error)]
#[error("Search error")]
struct SearchError;

#[derive(Deserialize, Serialize)]
struct SearchTool;

impl Tool for SearchTool {
    const NAME: &'static str = "search";

    type Error = SearchError;
    type Args = SearchArgs;
    type Output = SearchResult;

    async fn definition(&self, _prompt: String) -> ToolDefinition {
        serde_json::from_value(json!({
            "name": "search",
            "description": "Search for a website, it will return the title and URL",
            "parameters": {
                "type": "object",
                "properties": {
                    "query_string": {
                        "type": "string",
                        "description": "The query string to search for"
                    },
                }
            }
        }))
        .expect("Tool Definition")
    }

    async fn call(&self, args: Self::Args) -> Result<Self::Output, Self::Error> {
        println!("[tool-call] Searching for: '{}'", args.query_string);

        if args.query_string.to_lowercase().contains("rig") {
            Ok(SearchResult {
                title: "Rig Documentation".to_string(),
                url: "https://docs.rig.ai".to_string(),
            })
        } else {
            Err(SearchError)
        }
    }
}

Expected behavior

The expectation is a human readable answer sent back to the user.

Example:

Prompt: Can you please let me know title and url of rig platform?
Response: The title of the Rig platform is "Rig Documentation" and the URL is [https://docs.rig.ai](https://docs.rig.ai).

Additional context

OpenAI function calling