Function warn_unused_params 

pub fn warn_unused_params(
    haystack: &str,
    params: Option<&HashMap<String, String>>,
)

F10 (0.7.5 audit): warn loudly when --param key=value was passed but ${key} never appears anywhere the resolver searched. A common typo (--param maxid=… vs ${max_id}) is otherwise silently ignored and the operator gets unexpected results.

Decoupled from resolve_vars because the same params object flows through the YAML body resolve AND each ExportConfig::resolve_query call — emitting the warning inside resolve_vars itself fired it N+1 times per --param. Call this exactly once per CLI invocation, passing the original (un-resolved) YAML text as the haystack so placeholders are still present.