pub fn install(
existing: Option<&str>,
command: &str,
tools: &[Tool],
) -> Result<(String, bool), String>Expand description
Install the steering hook into existing settings text (or create a
fresh document), gating each tool in tools. Returns the new text and
whether it changed. Idempotent: re-installing the same command/tools is a
no-op; a --mode change rewrites the command in place; a new tool adds
its matcher. Comments and layout in existing are preserved.