Function render 

pub fn render(tool: &str, ctx: &str, err: &Error) -> String

Render an xa11y error for the model, prefixed by the failing tool and what it was doing (ctx, e.g. "resolve application").

The mapping is total: every Error variant produces either concrete next-step guidance or — where the error already says exactly what is wrong (InvalidSelector, InvalidActionData) — the verbatim display plus the fix that applies to the CALL SHAPE (an argument problem is not a platform problem; the model fixes it by editing the call, not by changing system settings).