Function with_ephemeral_workspace_warning 

pub fn with_ephemeral_workspace_warning(text: &str) -> String

Prepend EPHEMERAL_WORKSPACE_WARNING to a tool’s output/error text as a clearly delimited banner, preserving the original text below it.

The banner must live in the field the dispatcher forwards to the model (output on success, error on failure), so call this for whichever field will be shown. Returns the banner alone when text is empty.