Function run_pre_request 

pub fn run_pre_request(
    script: &Script,
    request: &Request,
) -> (Result<Request, SendraError>, ScriptOutput)

Run a pre_request script and return the request it left behind, along with anything it printed.

The script sees request as an object map — see [request_map] for the exact shape — mutates it in place, and this reads it back out and validates it. Errors are SendraError rather than a ScriptOutcome because there is no response and never will be: whatever went wrong, this request is not being sent, which is the same category of failure as a missing variable or a refused connection.

The ScriptOutput comes back whether the script succeeded or not, which is why it is beside the Result rather than inside its Ok: a script that printed three lines and then threw printed three lines, and those are usually the three lines that explain the throw. Losing them on the error path would lose them exactly when they are worth the most.