Function process_content 

pub fn process_content(content: &str, base_dir: &Path) -> String

Process content, resolving source paths relative to base_dir.

Markers are comment-agnostic: any line containing embed-src src="path" is an opening marker, and any line containing /embed-src is a closing marker. This allows embedding in any file type (markdown, Rust, Python, YAML, etc.).

By default, content is inserted raw. Use the fence attribute to wrap in markdown code fences: fence or fence="auto" auto-detects the language from the source extension; fence="python" uses an explicit language tag.