Function create_launch_draft 

pub fn create_launch_draft(
    target: DebugTargetKind,
    server: DebugServerKind,
) -> Result<Value, String>

Build the VS Code launch configuration draft for a target/server, mirroring TS createDebugProfile → debugProfileToLaunchDraft. Errors (with the TS message) when the server is not valid for the target.