The Neapolitan chord is spelled as a major triad on the lowered 2nd scale degree (♭2̂), never as a sharped-1 or other respelling

The Neapolitan's root must be spelled as the ordinary 2nd-degree letter with a flat/natural, never a sharped tonic or other substitute that obscures its flat-2 identity.

In C major/minor, the Neapolitan's root is spelled C#4 (sharped-tonic reading) instead of Db4 (flat-2 reading) -- pitch-class identical, but a completely different harmonic story.

Universal tonal-harmony convention; Gradus's romanNumeral.ts already identifies this chord (VERIFIED: functions `tryBorrowed` at line 521 / `tryBorrowedMinor` at line 675, explicit comment '♭II (Neapolitan): major triad on ♭2̂').

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