Function render_str 

pub fn render_str(
    source: &str,
    file: &Path,
    opts: RenderOptions<'_>,
) -> Result<MarkdownRenderResult, MarkdownError>

Renders markdown text to HTML, synchronously and without network access.

The one full-render pipeline: render_sync is this plus a file read, and render_with_cache shares every pass and differs only in fetching OpenGraph metadata over the network.

No-network embeds (YouTube, Giphy, GitHub gist, and bare-URL media) ARE produced — they are pure CPU (regex/string) and require no I/O, so they work regardless of oembed_timeout_ms. OpenGraph results are never fetched here; when oembed_timeout_ms > 0 and a cache is present, previously cached network results are merged in.

file only names the source in diagnostics (e.g. a YAML frontmatter parse warning); it is never read.