The seam (editor-core): a session-local caret — (voice, position, entry
duration), never in the op log, undo leaves it advanced, a deleted voice
clears it — with enter_nominal/enter_pitch/enter_rest funneling to one
insertion core that reuses the pencil's make-room verbatim and advances
only on success. Octave inference is nearest-in-staff-steps to the
preceding note with a downward tie-break — proven unreachable for real
letter pairs (candidate octaves sit an odd 7 steps apart), so the
comparator is tested directly. midi_note_to_pitch (sharps-spelled v1
policy) is the testable core of MIDI entry; x_at_position mirrors
invert_x for the GUI's caret line, extrapolation-tested on non-uniform
anchors after the uniform fixture proved blind to the wrong-segment
mutation.
The GUI (editor-gui): N-toggled entry mode, mutually exclusive with
pencil via a pure toggle_exclusive; mode-gated letters A-G, R for rests,
arrow-key caret movement, the duration palette doing double duty; the
caret drawn full staff height at x_at_position from the staff's own
rendered strokes. G5 locks the entry loop: C-D-E-F entered at the caret,
each advancing position value-asserted as an exact rational before any
pixel, baseline user-reviewed. Twelve mutations killed across the pair,
coordinator re-verified.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Levi Neuwirth
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