Function install_agents_md_guidance 

pub fn install_agents_md_guidance(
    project_dir: &Path,
    sqz_path: &str,
) -> Result<bool>

Install sqz’s guidance block into AGENTS.md at project_dir.

If AGENTS.md doesn’t exist yet, create it with sqz’s block as the sole content. If it exists, append sqz’s block (separated by a blank line so it renders as a new markdown section). If sqz blocks are already present, the first becomes the current block and the rest are removed, so sqz init stays idempotent.

Returns true when the file was created or modified, false when it was left as it was.