The VM walks every line -- it has no idea how many instructions there are. Verify that by extending the hand-written WAT to 3+4+5.

Don't change a single line of the VM. Just extend the multi-line string in the if (write_wat_manually) branch.

if (write_wat_manually) {
    appendStringLiteral(&wat_buffer, &wat_length,
        \\i64.const 3
        \\i64.const 4
        \\i64.add
    );
    // YOU: extend the WAT above so it computes 3+4+5.
} else {
    // (compiler -- still only handles "3+4" for now)
}

Set write_wat_manually = true and run.