Function compile_function_to_wasm 

pub fn compile_function_to_wasm(
    program: &CompiledProgram,
    fi: usize,
) -> Option<Vec<u8>>

Lower function fi of a compiled program to a WebAssembly module — the integration entry the VM’s tier-up uses. A function’s body lives in the shared program.code from its entry_pc until the next function’s entry (or the program end), with absolute jump targets; this extracts that slice and rebases every jump into the region-local 0-based space compile_region_to_wasm expects. Returns None (stay on bytecode) if the body leaves the integer fragment or a jump escapes the function.