Function main-separatorpub

main-separator — the host target's primary path separator, as a Codepoint. On Unix the value is / (U+002F); on Windows it would be \ (U+005C). Silo is currently Unix-only, so this always returns /.

Naming: the spec's Rust-style example uses the identifier MAIN_SEPARATOR; Silo's current grammar only permits lower-case identifiers as :fn names, so we expose this as main-separator. Once Silo grows an uppercase-const syntax (and @cfg dispatch for Windows), both changes will land together.