Function compile_frontend 

pub fn compile_frontend(source: &str) -> MultiErrorResult<CompileState>

Compile source code through all frontend phases (up to but not including codegen).

This runs: lexing → parsing → AST to RIR → semantic analysis → CFG construction. Returns the compile state which can be inspected for debugging.

This function collects errors from multiple functions instead of stopping at the first error, allowing users to see all issues at once.

Uses default optimization level (O0) and no preview features. For custom options, use compile_frontend_with_options.