NMOS SBC FLAGS PRECEDE DECIMAL CORRECTION

HYPOTHESIS: all official SBC modes and stable immediate alias $EB must share one subtraction contract. C means no borrow; N/V/Z derive from the raw binary difference, while decimal mode corrects the accumulator only after the low nibble's borrow has propagated to the high nibble.

Raw traces, ROM material, local paths, and personal data are not part of this public record.