Sigil

Sigil module: handlers for sigil expressions (~R, ~J, etc.)

Most sigils ~X"..." desugar to a call to Sigil.x(content). Handlers receive the interpolated string and return an appropriate type.

The ~H sigil for HTML templates is special: it desugars directly to IOList.from_strings([...]) with separate segments for static and dynamic parts, avoiding intermediate string concatenation.