Same-bar accidental in a different octave: courtesy accidental convention and disagreement

Strictly, accidental scope covers only its own octave for the bar -- a sharp on F#4 does not affect F5 later in the bar. Many engravers add a courtesy accidental in the other octave anyway to prevent eye misreading across the octave break.

F#4 in tenor and, three beats later in the same bar, F5 in soprano with no accidental -- correct under Gould's strict rule, but a Ross-convention reviewer might expect a courtesy sharp.

Gould states the strict rule and notes repetition is often unnecessary; Ross recommends the courtesy octave-accidental for performer safety, especially in fast/dense/orchestral passages; Read is largely silent. AUTHORITIES DISAGREE.

RECOMMEND treating it as suggestion-only for Gradus, since content is pedagogical single-learner score-reading, not orchestral sight-reading under performance pressure -- Ross's driving rationale doesn't apply, but flagging costs nothing.

Our own judgement, not a sourced convention — shown separately so the two are never confused.

This rule can be decided from pitches, durations and voices — no layout required. A validator can check it before anything is drawn.