Move the selected pitch by N diatonic staff positions (+1 up, -1 down): a
nominal move that carries the octave at the B-C boundary and preserves the
accidental — the "diatonic move" a vertical drag performs. It emits
ModifyIdentifiedPitch, which keeps the note's id, so the selection survives the
relayout. The staff step is the same data path the per-edit causal context was
built for: two sequential moves to one pitch reduce as intentional overwrites,
not a StructuralFieldCollision (proven by replaying the op log).
An authored spelling override (user-chosen, imported, or propagated) resolves
ahead of the inferred spelling and pins the rendered staff position, so a
value-only move would change the sound without moving the notehead. The intent
refuses that case (PitchSpellingOverridden) rather than mislead — the predicate
mirrors resolve_spelling's precedence ranking. A respelling-aware move that
atomically rebases the override is a follow-up (it needs a transaction-aware
apply). The diatonic index is computed in i64 so an extreme step count cannot
overflow before the octave range-check.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NAtEiJtt9yKVV1zjKYmZhS
Levi Neuwirth
42208c166d