Function detect_with_marker 

pub fn detect_with_marker(workspace: &Path, marker: &str) -> bool

Return true when workspace contains the given marker file. A generic, language-agnostic detection helper for marker-based plugins (e.g. JS → "package.json", TS → "tsconfig.json"). Lives here, not in any one language plugin, so every plugin can reuse it without depending on a sibling plugin.