Function compile_frontend_from_ast 

pub fn compile_frontend_from_ast(
    ast: Ast,
    interner: ThreadedRodeo,
) -> MultiErrorResult<CompileState>

Compile from an already-parsed AST through all remaining frontend phases.

This runs: AST to RIR → semantic analysis → CFG construction. Use this when you already have a parsed AST (e.g., for --emit modes that need both AST output and later stage output without double-parsing).

Uses no preview features. For custom options, use compile_frontend_from_ast_with_options.